Patent Publication Number: US-8537898-B2

Title: Compression with doppler enhancement

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division application of U.S. patent application Ser. No. 12/004,575, filed on Dec. 21, 2007, entitled “COMPRESSION WITH DOPPLER ENHANCEMENT,” which is a continuation-in-part of application Ser. No. 11/638,989, filed Dec. 13, 2006, entitled “VARIABLE GENERAL PURPOSE COMPRESSION FOR VIDEO IMAGES (ZLN),” docket ZLN2, which hereby is incorporated by reference. 
     Application Ser. No. 11/638,989 is a continuation of U.S. patent application Ser. No. 09/467,721, filed on Dec. 20, 1999, entitled “VARIABLE GENERAL PURPOSE COMPRESSION FOR VIDEO IMAGES (ZLN)”, now U.S. Pat. No. 7,233,619, which hereby is incorporated by reference. 
     This application, application Ser. No. 11/638,989, application Ser. No. 09/467,721 claim priority under 35 U.S.C. §119(e) of U.S. provisional application 60/113,051, filed on Dec. 21, 1998, and entitled “METHODS OF ZERO LOSS (ZL) COMPRESSION AND ENCODING OF GRAYSCALE IMAGES”, which hereby is incorporated by reference. 
     A continuation in part of application Ser. No. 09/467,721, filed Oct. 27, 2005, entitled “HANDHELD VIDEO TRANSMISSION AND DISPLAY,” application Ser. No. 11/262,106, was published as U.S. publication 2006/0114987. 
     A continuation in part of application Ser. No. 11/262,106, filed Jun. 27, 2007, entitled “HANDHELD VIDEO TRANSMISSION AND DISPLAY,” application Ser. No. 11/823,493, was published as U.S. publication 2007/0247515. 
     A continuation in part of application Ser. No. 09/467,721, filed Jun. 18, 2007, entitled “SEPARATE PLANE COMPRESSION USING A PLURALITY OF COMPRESSION METHODS INCLUDING ZLN AND ZLD METHODS,” application Ser. No. 11/820,300, docket ZLN3. 
     My U.S. patent application Ser. No. 09/470,566, filed on Dec. 22, 1999, and entitled GENERAL PURPOSE COMPRESSION FOR VIDEO IMAGES (RHN)”, known as the “RHN” method, now U.S. Pat. No. 7,016,417, hereby is incorporated by reference. The RHN application claims a priority date based on a U.S. provisional application 60/113,276 filed on Dec. 23, 1998, which also hereby is incorporated by reference. 
     The parent application Ser. No. 11/638,989 included by reference application Ser. No. 09/473,190, filed on Dec. 20, 1999, entitled “ADDING DOPPLER ENHANCEMENT TO GRAYSCALE COMPRESSION (ZLD).” Co-pending application Ser. No. 11/820,300, (ZLN3) also includes and claims subject matter from application Ser. No. 09/473,190. Application Ser. No. 09/473,190 hereby is included by reference. Application Ser. No. 09/473,190 claims priority based on provisional application 60/113,050 filed on Dec. 21, 1998 and entitled “METHODS OF ADDING DOPPLER ENHANCEMENT TO GRAYSCALE COMPRESSION (ZLD),” which is hereby incorporated by reference. 
     This application, application Ser. No. 11/820,300 (ZLN3), and application Ser. No. 09/473,190 claim priority under 35 U.S.C. §119(e) of the U.S. provisional application 60/113,050 filed on Dec. 21, 1998 
     My U.S. patent application Ser. No. 09/312,922, filed on May 17, 1999, entitled “SYSTEM FOR TRANSMITTING VIDEO IMAGES OVER A COMPUTER NETWORK TO A REMOTE RECEIVER,” now U.S. Pat. No. 7,257,158, describes an embodiment of the invention of the RHN method, as well as a system for practicing the compression method, and also hereby is incorporated by reference. 
     U.S. patent application Ser. No. 09/436,432, filed on Nov. 8, 1999, and entitled “SYSTEM FOR TRANSMITTING VIDEO IMAGES OVER A COMPUTER NETWORK TO A REMOTE RECEIVER,” now U.S. Pat. No. 7,191,462, is wholly owned by the inventor of the present invention. 
     ZLN is a three-letter identifier used to refer to the family of compression methods disclosed in the ZLN application. ZLD is a three-letter identifier used to refer to the family of compressions methods disclosed herein. ZL originally stood for ZeroLoss, a trademark of Kendyl Roman referring to the clinically lossless nature of the methods. The N in ZLN refers to the variable nature of the method when N can be one of a plurality of values. The D in ZLD refers to the added capabilities for handling Doppler enhanced images in conjunction with a compression method such as one of the ZLN family of methods. 
     The ZLN and ZLD family of compression methods can be practiced on any number apparatus or medium known in the art, including those disclosed herein, in U.S. provisional application 60/085,818, international application PCT/US99/10894, international publication number WO 99/59472, U.S. application Ser. No. 09/312,922, U.S. Pat. No. 7,257,158, or in U.S. patent application Ser. No. 09/436,432, U.S. Pat. No. 7,191,462. 
     U.S. patent application Ser. No. 09/433,978, filed on Nov. 4, 1999, and entitled “GRAPHICAL USER INTERFACE INCLUDING ZOOM CONTROL REPRESENTING IMAGE AND MAGNIFICATION OF DISPLAYED IMAGE”, now U.S. Pat. No. 6,803,931, is wholly owned by the inventor of the present invention. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     This invention relates to data compression, specifically to the compression and decompression of video images. 
     The ZLD format relates specifically to the compression and decompression of video images that contain an image overlaid with Doppler enhancement. 
     2. Description of Prior Art 
     In the last few years, there have been tremendous advances in the speed of computer processors and in the availability of bandwidth of worldwide computer networks such as the Internet. These advances have led to a point where businesses and households now commonly have both the computing power and network connectivity necessary to have point-to-point digital communications of audio, rich graphical images, and video. However the transmission of video signals with the full resolution and quality of television is still out of reach. In order to achieve an acceptable level of video quality, the video signal must be compressed significantly without losing either spatial or temporal quality. 
     A number of different approaches have been taken but each has resulted in less than acceptable results. These approaches and their disadvantages are disclosed by Mark Nelson in a book entitled The Data Compression Book, Second Edition, published by M&amp;T Book in 1996. Mark Morrision also discusses the state of the art in a book entitled The Magic of Image Processing, published by Sams Publishing in 1993. 
     Video Signals 
     Standard video signals are analog in nature. In the United States, television signals contain 525 scan lines of which 480 lines are visible on most televisions. The video signal represents a continuous stream of still images, also known as frames, which are fully scanned, transmitted and displayed at a rate of 30 frames per second. This frame rate is considered full motion. 
     A television screen has a 4:3 aspect ratio. 
     When an analog video signal is digitized, each of the 480 lines is sampled 640 times, and each sample is represented by a number. Each sample point is called a picture element, or pixel. A two dimensional array is created that is 640 pixels wide and 480 pixels high. This 640×480 pixel array is a still graphical image that is considered to be full frame. The human eye can perceive 16.7 thousand colors. A pixel value comprised of 24 bits can represent each perceivable color. A graphical image made up of 24-bit pixels is considered to be full color. A single, second-long, full frame, full color video requires over 220 millions bits of data. 
     The transmission of 640×480 pixels×24 bits per pixel times 30 frames requires the transmission of 221,184,000 million bits per second. A T1 Internet connection can transfer up to 1.54 million bits per second. A high-speed (56 Kb) modem can transfer data at a maximum rate of 56 thousand bits per second. The transfer of full motion, full frame, full color digital video over a T1 Internet connection, or 56 Kb modem, will require an effective data compression of over 144:1, or 3949:1, respectively. 
     A video signal typically will contain some signal noise. In the case where the image is generated based on sampled data, such as an ultrasound machine, there is often noise and artificial spikes in the signal. A video signal recorded on magnetic tape may have fluctuations due the irregularities in the recording media. Florescent or improper lighting may cause a solid background to flicker or appear grainy. Such noise exists in the real world but may reduce the quality of the perceived image and lower the compression ratio that could be achieved by conventional methods. 
     Basic Run-length Encoding 
     An early technique for data compression is run-length encoding where a repeated series of items are replaced with one sample item and a count for the number of times the sample repeats. Prior art shows run-length encoding of both individual bits and bytes. These simple approaches by themselves have failed to achieve the necessary compression ratios. 
     Variable Length Encoding 
     In the late 1940s, Claude Shannon at Bell Labs and R. M. Fano at MIT pioneered the field of data compression. Their work resulted in a technique of using variable length codes where codes with low probabilities have more bits, and codes with higher probabilities have fewer bits. This approach requires multiple passes through the data to determine code probability and then to encode the data. This approach also has failed to achieve the necessary compression ratios. 
     D. A. Huffman disclosed a more efficient approach of variable length encoding known as Huffman coding in a paper entitled “A Method for Construction of Minimum Redundancy Codes,” published in 1952. This approach also has failed to achieve the necessary compression ratios. 
     Arithmetic, Finite Context, and Adaptive Coding 
     In the 1980s, arithmetic, finite coding, and adaptive coding have provided a slight improvement over the earlier methods. These approaches require extensive computer processing and have failed to achieve the necessary compression ratios. 
     Dictionary-Based Compression 
     Dictionary-based compression uses a completely different method to compress data. Variable length strings of symbols are encoded as single tokens. The tokens form an index to a dictionary. In 1977, Abraham Lempel and Jacob Ziv published a paper entitled, “A Universal Algorithm for Sequential Data Compression” in IEEE Transactions on Information Theory, which disclosed a compression technique commonly known as LZ77. The same authors published a 1978 sequel entitled, “Compression of Individual Sequences via Variable-Rate Coding,” which disclosed a compression technique commonly known as LZ78 (see U.S. Pat. No. 4,464,650). Terry Welch published an article entitled, “A Technique for High-Performance Data Compression,” in the June 1984 issue of IEEE Computer, which disclosed an algorithm commonly known as LZW, which is the basis for the GIF algorithm (see U.S. Pat. Nos. 4,558,302, 4,814,746, and 4,876,541). In 1989, Stack Electronics implemented a LZ77 based method called QIC-122 (see U.S. Pat. No. 5,532,694, U.S. Pat. No. 5,506,580, and U.S. Pat. No. 5,463,390). 
     These lossless (method where no data is lost) compression methods can achieve up to 10:1 compression ratios on graphic images typical of a video image. While these dictionary-based algorithms are popular, these approaches require extensive computer processing and have failed to achieve the necessary compression ratios. 
     JPEG and MPEG 
     Graphical images have an advantage over conventional computer data files: they can be slightly modified during the compression/decompression cycle without affecting the perceived quality on the part of the viewer. By allowing some loss of data, compression ratios of 25:1 have been achieved without major degradation of the perceived image. The Joint Photographic Experts Group (JPEG) has developed a standard for graphical image compression. The JPEG lossy (method where some data is lost) compression algorithm first divides the color image into three color planes and divides each plane into 8 by 8 blocks, and then the algorithm operates in three successive stages:
         (a) A mathematical transformation known as Discrete Cosine Transform (DCT) takes a set of points from the spatial domain and transforms them into an identical representation in the frequency domain.   (b) A lossy quantization is performed using a quantization matrix to reduce the precision of the coefficients.   (c) The zero values are encoded in a zig-zag sequence (see Nelson, pp. 341-342).       

     JPEG can be scaled to achieve higher compression ratios by allowing more loss in the quantization stage of the compression. However this loss results in certain blocks of the image being compressed such that areas of the image have a blocky appearance and the edges of the 8 by 8 blocks become apparent because they no longer match the colors of their adjacent blocks. Another disadvantage of JPEG is smearing. The true edges in an image get blurred due to the lossy compression method. 
     The Moving Pictures Expert Group (MPEG) uses a combination of JPEG based techniques combined with forward and reverse temporal differencing. MPEG compares adjacent frames and, for those blocks that are identical to those in a previous or subsequent frame, only a description of the previous or subsequent identical block is encoded. MPEG suffers from the same blocking and smearing problems as JPEG. 
     These approaches require extensive computer processing and have failed to achieve the necessary compression ratios without unacceptable loss of image quality and artificially induced distortion. 
     QuickTime: CinePak, Sorensen, H.263 
     Apple Computer, Inc. released a component architecture for digital video compression and decompression, named QuickTime. Any number of methods can be encoded into a QuickTime compressor/decompressor (codec). Some popular codecs are CinePak, Sorensen, and H.263. CinePak and Sorensen both require extensive computer processing to prepare a digital video sequence for playback in real time; neither can be used for live compression. H.263 compresses in real time but does so by sacrificing image quality resulting in severe blocking and smearing. 
     Fractal and Wavelet Compression 
     Extremely high compression ratios are achievable with fractal and wavelet compression algorithms. These approaches require extensive computer processing and generally cannot be completed in real time. 
     Sub-Sampling 
     Sub-sampling is the selection of a subset of data from a larger set of data. For example, when every other pixel of every other row of a video image is selected, the resulting image has half the width and half the height. This is image sub-sampling. Other types of sub-sampling include frame sub-sampling, area sub-sampling, and bit-wise sub-sampling. 
     Image Stretching 
     If an image is to be enlarged but maintain the same number of pixels per inch, data must be filled in for the new pixels that are added. Various methods of stretching an image and filling in the new pixels to maintain image consistency are known in the art. Some methods known in the art are dithering (using adjacent colors that appear to be blended color), and error diffusion, “nearest neighbor”, bilinear and bicubic. 
     Doppler Enhancement 
     Doppler techniques are used to determine the velocities of one or more small objects. Some common uses of Doppler techniques include without limitation:
         1. Radar used to detect rain   2. Radar used to determine speed of vehicles or aircraft   3. Ultrasound blood flow analysis       

     Doppler velocity scales are often incorporated with grayscale images. 
     In the case of ultrasound blood flow analysis, average velocities toward the sensing probe are encoded as a shade of red and velocities away from the sensing probe are encoded as a shade of blue. Although the image appears to be in color, there are really three monochromic values: a grayscale, a red scale, and a blue scale. The base image plane (grayscale ultrasound) is generated more often (typically 15-30 frames per second) than the overlay plane showing the Doppler red and blue scales (typically 3-10 frames per second). 
     In the case of rain, the base map of the earth is generated only once and the Doppler colors that indicate the intensity of the precipitation are laid over the base map. 
     Moving Pictures 
     A video or movie is comprised of a series of still images that, when displayed in sequence, appear to the human eye as a live motion image. Each still image is called a frame. Television in the USA displays frames at the rate of 30 frames per second. Theater motion pictures are displayed at 24 frames per second. Cartoon animation is typically displayed at 8-12 frames per second. 
     Compression Methods 
     The ZLN and ZLD methods are effective ways to compress video images. Other compression algorithms are known in the prior art, including RLE, GIF (LZW), MPEG, Cinepak, Motion-JPEG, Sorensen, Fractal, and many others. 
     Each of these methods treats a frame of video as a basic unit of compression applying the compression method uniformly to the entire image. 
     Color Plane Separation 
     It is well known in the art that an image can be uniformly separated into color planes based on the red, green, and blue components values for each pixel, based on hue, saturation, and brightness component values for each pixel, or based on ink colors, such as cyan, yellow, magenta, and black. However these color plane separations are not done to reduce data size or to aid compression. They are used to facilitate the display (such as on a RGB or YUV computer monitor) or the printing of the image (for example, four-color printing). 
     Frame Differencing 
     MPEG and some other compression methods compare adjacent frames in a stream of frames. Under certain circumstances these methods send only a subset of a frame (namely a rectangular portion that contains a change when compared to the adjacent frame) which is then overlaid on the unchanged data for the adjacent frame. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention a method of compression of a video stream comprises steps of sub-sampling a video frame, and run-length encoding the sub-sampled pixel values, whereby the method can be executed in real time and the compressed representation of pixels saves substantial space on a storage medium and requires substantially less time and bandwidth to be transported over a communications link. The present invention includes a corresponding method for decompressing the encoded data. 
     Doppler velocity scales are incorporated into grayscale compression methods using two bits. 
     In accordance with an aspect of the present invention, a method of adding Doppler enhancement to compression code typically formatted for grayscale only, by using two bits of the data field to represent the scale of the remaining bits where said bits indicate one of the set of scales comprising: 
     1. grayscale, 
     2. red scale, and 
     3. blue scale. 
     Objects and Advantages 
     Accordingly, beside the objects and advantages of the method described above, some additional objects and advantages of the present invention are:
         (a) to provide a method of compressing and decompressing video signals so that the video information can be transported across a digital communications channel in real time.   (b) to provide a method of compressing and decompressing video signals such that compression can be accomplished with software on commercially available computers without the need for additional hardware for either compression or decompression.   (c) to provide a high quality video image without the blocking and smearing defects associated with prior art lossy methods.   (d) to provide a high quality video image that suitable for use in medical applications.   (e) to enhance images by filtering noise or recording artifacts.   (f) to provide a method of compression of video signals such that the compressed representation of the video signals is substantially reduced in size for storage on a storage medium.   (g) to provide a level of encryption so that images are not directly viewable from the data as contained in the transmission.   (h) to provide efficient encoding of Doppler enhanced images.   (i) to reduce the size of an encoded data buffer that contains Doppler enhancement.   (j) to provide efficient encoding for video images that contain distinguishable regions.   (k) to reduce the size of an encoded data representing a video stream.   (l) to reduce the bandwidth required to transmit an encoded video stream.   (m) to provide user control of compression methods.       

    
    
     
       DRAWING FIGURES 
       In the drawings, closely related figures have the same number but different alphabetic suffixes. 
         FIG. 1  shows the high level steps of compression and decompression of an image. 
         FIG. 2A to 2H  show alternatives for selecting a pixel value for encoding. 
         FIG. 2A  shows the four channel format of a pixel. 
         FIG. 2B  shows the three color components of a pixel. 
         FIG. 2G  shows selection of a component of a grayscale pixel. 
         FIG. 2F  shows a selection of the red component of a red scale pixel. 
         FIG. 3A  shows the basic format of the ZLN variable encoding format 
         FIG. 3B  shows an example of a code where N is 5 bits wide and U is 3 bits wide. 
         FIG. 4A  shows the flowchart for the compression method. 
         FIG. 4B  shows an image and a corresponding stream of pixels. 
         FIG. 5A to 5C  shows the formats for the run-length encoding of the RHN method. 
         FIG. 5D  shows the ZLD format. 
         FIG. 5E  shows the three formats of the three scales. 
         FIG. 5F  shows an alternate embodiment of the grayscale format. 
         FIG. 5G  shows the ZLD format embedded in the ZLN format. 
         FIG. 6  shows a series of codes and the resulting encoded stream. 
         FIG. 7  shows a series of codes and the resulting encoded stream of the RI-IN method. 
         FIG. 8A  shows examples of variable formats. 
         FIG. 8B  shows a format that preserves 9 bits of color. 
         FIG. 9  shows the flow chart for the decompression method. 
         FIG. 10  shows image stretching by interpolation. 
         FIG. 11A  shows an example encode table. 
         FIG. 11B  shows a corresponding grayscale decode table. 
         FIG. 11C  shows a corresponding red scale decode table. 
         FIGS. 12A and 12B  show machines for compressing and decompressing, respectively. 
         FIG. 12C  shows a compressor and decompressor connected to a storage medium. 
         FIG. 12D  shows a compressor and decompressor connected to a communications channel. 
         FIG. 13A  shows elements of a compressor. 
         FIG. 13B  shows an embodiment of an encoding circuit. 
         FIG. 13C  shows a generic pixel sub-sampler. 
         FIGS. 13D through 13J  show embodiments of pixel sub-samplers. 
         FIGS. 14A through 14C  shows embodiments of a machine element for variably altering the number of bits. 
         FIG. 15  shows elements of a decompressor. 
         FIG. 16A  shows elements for setting width, height, frame rate, brightness, and contrast which are variably altered by a receiver. 
         FIG. 16B  shows elements for setting the number of pixel bits that are variably altered by a receiver. 
         FIG. 17  shows a lossless compression step for further compression of an encoded data buffer. 
         FIG. 18  shows images being enlarged by stretching. 
       
         
           
             
                 
               
                 
                     
                 
                 
                   Reference Numerals in Drawings 
                 
                 
                     
                 
               
              
                 
                     
                 
              
             
             
                 
                 
              
                 
                    100 
                   compression steps 
                 
                 
                    110 
                   sub-sampling step 
                 
                 
                    130 
                   encoding step 
                 
                 
                    140 
                   encoded data 
                 
                 
                    150 
                   decompression steps 
                 
                 
                    160 
                   decoding step 
                 
                 
                    180 
                   image reconstitution step 
                 
                 
                    200 
                   32 bit pixel value (four channel format) 
                 
                 
                    202 
                   blue channel 
                 
                 
                    204 
                   green channel 
                 
                 
                    206 
                   red channel 
                 
                 
                    208 
                   alpha channel 
                 
                 
                    210 
                   24 bit pixel value 
                 
                 
                    212 
                   blue component 
                 
                 
                    214 
                   green component 
                 
                 
                    216 
                   red component 
                 
                 
                    220 
                   RGB averaging diagram 
                 
                 
                    222 
                   blue value 
                 
                 
                    224 
                   green value 
                 
                 
                    226 
                   red value 
                 
                 
                    228 
                   averaged value 
                 
                 
                    230 
                   blue selection diagram 
                 
                 
                    232 
                   blue instance 
                 
                 
                    234 
                   green instance 
                 
                 
                    236 
                   red instance 
                 
                 
                    240 
                   selected blue value 
                 
                 
                    250 
                   green selection diagram 
                 
                 
                    260 
                   selected green value 
                 
                 
                    270 
                   red selection diagram 
                 
                 
                    280 
                   selected red value 
                 
                 
                    290 
                   grayscale pixel 
                 
                 
                    292 
                   grayscale blue 
                 
                 
                    294 
                   grayscale green 
                 
                 
                    296 
                   grayscale red 
                 
                 
                    298 
                   selected grayscale value 
                 
                 
                    299 
                   filtered pixel value 
                 
                 
                    300 
                   N 
                 
                 
                    301 
                   U 
                 
                 
                    302 
                   W 
                 
                 
                    310 
                   pixel bit 7 
                 
                 
                    312 
                   pixel bit 6 
                 
                 
                    314 
                   pixel bit 5 
                 
                 
                    316 
                   pixel bit 4 
                 
                 
                    318 
                   pixel bit 3 
                 
                 
                    320 
                   pixel bit 2 
                 
                 
                    322 
                   pixel bit 1 
                 
                 
                    324 
                   pixel bit 0 
                 
                 
                    325 
                   8 bit pixel 
                 
                 
                    330 
                   5 bit sample 
                 
                 
                    332 
                   sample bit 4 
                 
                 
                    334 
                   sample bit 3 
                 
                 
                    336 
                   sample bit 2 
                 
                 
                    338 
                   sample bit 1 
                 
                 
                    340 
                   sample bit 0 
                 
                 
                    350 
                   3 low order bits 
                 
                 
                    360 
                   formatted code 
                 
                 
                    362 
                   encoded bit 4 
                 
                 
                    364 
                   encoded bit 3 
                 
                 
                    366 
                   encoded bit 2 
                 
                 
                    368 
                   encoded bit 1 
                 
                 
                    370 
                   encoded bit 0 
                 
                 
                    380 
                   3 bit count value 
                 
                 
                    400 
                   encode flowchart 
                 
                 
                    402 
                   encode entry 
                 
                 
                    403 
                   encode initialization step 
                 
                 
                    404 
                   get pixel step 
                 
                 
                    405 
                   get value step 
                 
                 
                    406 
                   lookup encoded value step 
                 
                 
                    408 
                   compare previous 
                 
                 
                    410 
                   increment counter step 
                 
                 
                    412 
                   check count overflow 
                 
                 
                    414 
                   new code step 
                 
                 
                    416 
                   check end of data 
                 
                 
                    418 
                   set done 
                 
                 
                    420 
                   counter overflow step 
                 
                 
                    422 
                   check done 
                 
                 
                    428 
                   encode exit 
                 
                 
                    430 
                   image 
                 
                 
                    440 
                   image width 
                 
                 
                    450 
                   image height 
                 
                 
                    460 
                   pixel stream 
                 
                 
                    500 
                   code byte 
                 
                 
                    501 
                   S1 
                 
                 
                    502 
                   S0 
                 
                 
                    503 
                   S 
                 
                 
                    505 
                   E 
                 
                 
                    510 
                   flag bit 
                 
                 
                    511 
                   Doppler/grayscale flag zero 
                 
                 
                    512 
                   don&#39;t care 
                 
                 
                    514 
                   grayscale value 
                 
                 
                    515 
                   grayscale code 
                 
                 
                    520 
                   repeat code 
                 
                 
                    521 
                   Doppler/grayscale flag one 
                 
                 
                    522 
                   blue/red flag zero 
                 
                 
                    524 
                   red scale value 
                 
                 
                    525 
                   red Doppler scale code 
                 
                 
                    530 
                   count 
                 
                 
                    531 
                   second Doppler/grayscale flag one 
                 
                 
                    532 
                   blue/red flag one 
                 
                 
                    534 
                   blue scale value 
                 
                 
                    535 
                   blue Doppler scale code 
                 
                 
                    541 
                   second Doppler/grayscale flag zero 
                 
                 
                    544 
                   extended value 
                 
                 
                    545 
                   extended grayscale code 
                 
                 
                    550 
                   data code 
                 
                 
                    551 
                   S1 in ZLN format 
                 
                 
                    552 
                   S0 in ZLN format 
                 
                 
                    553 
                   S in ZLN format 
                 
                 
                    554 
                   E in ZLN format 
                 
                 
                    555 
                   C 
                 
                 
                    557 
                   X 
                 
                 
                    560 
                   wasted bits 
                 
                 
                    565 
                   data bit 6 
                 
                 
                    570 
                   data bit 5 
                 
                 
                    575 
                   data bit 4 
                 
                 
                    580 
                   data bit 3 
                 
                 
                    585 
                   data bit 2 
                 
                 
                    590 
                   data bit 1 
                 
                 
                    595 
                   data bit 0 
                 
                 
                    610 
                   decimal values 
                 
                 
                    620 
                   first value 
                 
                 
                    622 
                   second value 
                 
                 
                    624 
                   third value 
                 
                 
                    626 
                   fourth value 
                 
                 
                    628 
                   fifth value 
                 
                 
                    630 
                   sixth value 
                 
                 
                    632 
                   seventh value 
                 
                 
                    640 
                   binary code 
                 
                 
                    650 
                   first byte 
                 
                 
                    651 
                   first data 
                 
                 
                    652 
                   first count 
                 
                 
                    653 
                   second byte 
                 
                 
                    654 
                   second data 
                 
                 
                    655 
                   second count 
                 
                 
                    656 
                   third byte 
                 
                 
                    657 
                   third data 
                 
                 
                    658 
                   third count 
                 
                 
                    740 
                   RHN binary code 
                 
                 
                    803 
                   ZL3 format 
                 
                 
                    804 
                   ZL4 format 
                 
                 
                    805 
                   ZL5 format 
                 
                 
                    808 
                   ZL8 format 
                 
                 
                    809 
                   ZL9 format 
                 
                 
                    812 
                   ZL12 format 
                 
                 
                    820 
                   ZL9C format 
                 
                 
                    900 
                   decode entry 
                 
                 
                    901 
                   decode initialize step 
                 
                 
                    902 
                   get code step 
                 
                 
                    908 
                   decode lookup step 
                 
                 
                    909 
                   check zero count 
                 
                 
                    910 
                   place pixel step 
                 
                 
                    914 
                   reset counter step 
                 
                 
                    916 
                   check length 
                 
                 
                    918 
                   decode exit 
                 
                 
                    920 
                   decode flowchart 
                 
                 
                   1010 
                   first adjacent pixel 
                 
                 
                   1012 
                   second adjacent pixel 
                 
                 
                   1014 
                   first subsequent adjacent pixel 
                 
                 
                   1016 
                   second subsequent adjacent pixel 
                 
                 
                   1052 
                   interpolated pixel 
                 
                 
                   1054 
                   interpolated pixel 
                 
                 
                   1056 
                   interpolated pixel 
                 
                 
                   1058 
                   interpolated pixel 
                 
                 
                   1060 
                   interpolated pixel 
                 
                 
                   1100 
                   encryption table 
                 
                 
                   1110 
                   decryption table 
                 
                 
                   1112 
                   grayscale red bits 
                 
                 
                   1114 
                   grayscale green bits 
                 
                 
                   1116 
                   grayscale blue bits 
                 
                 
                   1120 
                   red scale decode table 
                 
                 
                   1122 
                   red scale red bits 
                 
                 
                   1124 
                   red scale green bits 
                 
                 
                   1126 
                   red scale blue bits 
                 
                 
                   1200 
                   video frames 
                 
                 
                    1205a 
                   first video frame 
                 
                 
                    1205b 
                   second video frame 
                 
                 
                    1205n 
                   nth video frame 
                 
                 
                   1210 
                   compressor 
                 
                 
                   1215 
                   video signal 
                 
                 
                   1220 
                   series of encoded data 
                 
                 
                    1225a 
                   first encoded data 
                 
                 
                    1225b 
                   second encoded data 
                 
                 
                    1225n 
                   nth encoded data 
                 
                 
                   1225 
                   encoded data buffer 
                 
                 
                    1230a 
                   first received encoded data 
                 
                 
                    1230b 
                   second received encoded data 
                 
                 
                    1230n 
                   nth received encoded data 
                 
                 
                   1230 
                   received encoded data 
                 
                 
                   1235 
                   encoded data stream 
                 
                 
                   1238 
                   received encoded data (series) 
                 
                 
                   1240 
                   I/O device 
                 
                 
                   1245 
                   input encoded data stream 
                 
                 
                   1250 
                   decompressor 
                 
                 
                    1260a 
                   first decoded video frame 
                 
                 
                    1260b 
                   second decoded video frame 
                 
                 
                    1260n 
                   nth decoded video frame 
                 
                 
                   1260 
                   decoded video frame 
                 
                 
                   1268 
                   decoded video frames 
                 
                 
                   1270 
                   video sequence 
                 
                 
                   1280 
                   storage medium 
                 
                 
                   1290 
                   communications channel 
                 
                 
                   1310 
                   video digitizer 
                 
                 
                   1320 
                   path 1320 
                 
                 
                   1330 
                   video memory 
                 
                 
                   1331 
                   scan 
                 
                 
                   1332 
                   pixel index 
                 
                 
                   1340 
                   path 1340 
                 
                 
                   1350 
                   encoding circuit 
                 
                 
                   1360 
                   path 1360 
                 
                 
                   1370 
                   encoded data 
                 
                 
                    1380a 
                   24 to 5 bit sub-sampler 
                 
                 
                    1380b 
                   24-bit RGB to 5 bit sub-sampler 
                 
                 
                    1380c 
                   32-bit RGB to 5 bit sub-sampler 
                 
                 
                    1380d 
                   color 9-bit sub-sampler 
                 
                 
                    1380e 
                   YUV sub-sampler 
                 
                 
                    1380f 
                   36-bit RGB to 24-bit sub-sampler 
                 
                 
                    1380g 
                   15-bit sub-sampler 
                 
                 
                   1380 
                   pixel sub-sampler 
                 
                 
                   1382 
                   pixel extractor 
                 
                 
                   1383 
                   value path 
                 
                 
                   1384 
                   coder 
                 
                 
                   1385 
                   path 1385 
                 
                 
                   1390 
                   data/count 
                 
                 
                   1392 
                   code index 
                 
                 
                   1395 
                   path 1395 
                 
                 
                   1400 
                   24-bit to variable bit sub-sampler 
                 
                 
                   1401 
                   generic 3-bit sub-sampler 
                 
                 
                   1402 
                   generic 4-bit sub-sampler 
                 
                 
                   1403 
                   generic 8-bit sub-sampler 
                 
                 
                   1404 
                   generic 10-bit sub-sampler 
                 
                 
                   1410 
                   number of bits selector 
                 
                 
                   1420 
                   number of bits indicator 
                 
                 
                   1430 
                   36-bit to variable bit sub-sampler 
                 
                 
                   1440 
                   24/36 bit variable bit sub-sampler 
                 
                 
                   1450 
                   second selector 
                 
                 
                   1460 
                   selection logic 
                 
                 
                   1470 
                   selection signal 
                 
                 
                   1510 
                   decoding circuit 
                 
                 
                   1520 
                   decoded pixel values 
                 
                 
                   1530 
                   decoder pixel index 
                 
                 
                   1540 
                   image memory 
                 
                 
                   1600 
                   transmitter 
                 
                 
                   1610 
                   receiver 
                 
                 
                   1615 
                   setting control path 
                 
                 
                   1620 
                   frame sub-sampler 
                 
                 
                   1621 
                   path 1621 
                 
                 
                   1630 
                   selected frame 
                 
                 
                   1632 
                   pixel from frame 
                 
                 
                   1640 
                   transmitter pixel sub-sampler 
                 
                 
                   1642 
                   path 1642 
                 
                 
                   1650 
                   run length encoder 
                 
                 
                   1660 
                   settings 
                 
                 
                   1661 
                   brightness 
                 
                 
                   1662 
                   contrast 
                 
                 
                   1663 
                   height 
                 
                 
                   1664 
                   width 
                 
                 
                   1665 
                   frame rate 
                 
                 
                   1670 
                   frame selector 
                 
                 
                   1675 
                   frame select indicator 
                 
                 
                   1680 
                   number of pixel bits setting 
                 
                 
                   1690 
                   alternate transmitter 
                 
                 
                   1700 
                   run-length encoding step 
                 
                 
                   1710 
                   run-length encoded output 
                 
                 
                   1720 
                   further lossless compression step 
                 
                 
                   1730 
                   further lossless compression output 
                 
                 
                   1800 
                   unstretched frame 
                 
                 
                   1810 
                   enlarged image 
                 
                 
                   1820 
                   stretching step 
                 
                 
                     
                 
              
             
           
         
       
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG.  1   
     Compression and Decompression Steps 
       FIG. 1  illustrates a sequence of compression steps  100  and a sequence of decompression steps  150  of the present invention. The compression steps  100  comprise a sub-sampling step  110  and an encoding step  130 . After completion of the compression steps  100 , a stream of encoded data  140  is output to either a storage medium or a transmission channel. The decompression steps  150  comprise a decoding step  160  wherein the stream of encoded data  140  is processed and an image reconstitution step  180 . 
     FIGS.  2 A to  2 H 
     Selecting Pixel Values for Encoding 
       FIGS. 2A to 2G  illustrate alternatives for selecting a pixel value for encoding. The sub-sampling step  110  ( FIG. 1 ) includes sub-sampling of a pixel value to obtain a variable selected number of bits. 
     Video digitizing hardware typical has the options of storing the pixel values as a 32 bit pixel value  200  or a 24 bit pixel value  210 , shown in  FIG. 2A  and  FIG. 2B , respectively. The 32 bit pixel value  200  is composed of a blue channel  202 , a green channel  204 , a red channel  206 , and an alpha channel  208 . Each channel contains 8 bits and can represent 256 saturation levels for the particular color channel. For each channel the saturation intensity value of zero represents the fully off state, and the saturation intensity value of “255” represents the fully on state. A common alternative not shown is a sixteen-bit format where the three color channels contain 5 bits each and the alpha channel is a single bit. The present invention anticipates the use of the color channels of 16 bit pixel value is a manner substantially the same as the 32-bit pixel value  200  except the number of bits per channel is 5 instead of 8. 
     The 24-bit pixel value  210  is composed of a blue component  212 , a green component  214 , and a red component  216 . There is no component for the alpha channel in the 24 bit pixel value  210 . Regardless of the structure, the blue channel  202  is equivalent to the blue component  212 , the green channel  204  is equivalent to the green component  214 , and the red channel  206  is equivalent to the red component  216 . 
     In the present invention, the 32 bit pixel value  200  alternative is preferred due to the consistent alignment of 32 bit values in most computer memories; however for simplicity of illustration the alpha channel  208  will be omitted in  FIGS. 2C to 2G . 
     If the video signal is digitized in color, the three color components may have different values. For example in  FIG. 2C , a RGB averaging diagram  220  illustrates a blue value  222  of  35  decimal, a green value  224  of  15 , and a red value  226  of  10 . One alternative is to sub sample from 24 bits to 8 bits by averaging the three color values to obtain an averaged value  228  that, in this example, has the value of 20: (10+15+35)/3=20. This will produce a grayscale image. Alternatively, a color image can be preserved by sampling bits from each color component (see  FIG. 8B ). 
       FIG. 2D  illustrates another alternative for selecting an 8 bit value in a blue selection diagram  230 . In this example, a blue instance  232  has the value of 35, a green instance  234  has the value of 15, and a red instance  236  has the value of 10. In this alternative the blue instance  232  is always selected as a selected blue value  240 . 
       FIG. 2E  illustrates another alternative for selecting an 8 bit value in a green selection diagram  250 . In this alternative the green instance  234  is always selected as a selected green value  260 . 
       FIG. 2F  illustrates another alternative for selecting an 8 bit value in a red selection diagram  270 . In this alternative the red instance  236  is always selected as a selected red value  280 . 
     If the video signal being digitized is grayscale, the three color components will have the same values. For example in  FIG. 2G , a grayscale pixel  290  comprises a grayscale blue  292  with a value of decimal 40, a grayscale green  294  with a value of 40, and a grayscale red  296  with a value of 40. Because the values are all the same, it makes no difference which grayscale color component is selected, a selected grayscale value  298  will have the value of 40 in this example. 
     The preferred embodiment of this invention uses the low order byte of the pixel value, which is typically the blue component as shown in  FIG. 2D . 
       FIG. 2H  illustrates a filtered pixel value  299  of 8 bits that may be selected by one of the alternatives described above. In these examples, the filtered pixel value  299  is equivalent to items referenced by numerals  228 ,  240 ,  260 ,  280 , or  298 . This reduction of the 32 bit pixel value  200  or the 24 bit pixel value  210  contributes a reduction in data size of 4:1 or 3:1, respectively. This reduction recognizes that for some images, such as medical images or grayscale images, no relevant information is lost. 
     For additional compression, the filtered pixel value  299  can variably select any number of bits. For example, selection of the most significant four bits instead of all eight bits filters noise that may show up in the low order bits may be very suitable for an image such as one produced by an ultrasound medical device. An example of this is shown by ZL4  804  in  FIG. 8A . 
     FIGS.  3 A and  3 B 
     Encoding Formats 
     Speed of compression and decompression may be enhanced if the algorithms fit into computer memory native storage elements such as 8 bit bytes, 16 bit words, or 32 bit double words, or some other size for which the computer architecture is optimized. 
     A grayscale image may be stored at a higher bit level than the actual values require. This may occur when an image is generated by an imaging technology such as radar, ultrasound, x-ray, magnetic resonance, or similar electronic technology. For example an ultrasound machine may only produce 16 levels of grayscale, requiring 4 bits of data per pixel, but the image digitizing may be performed at 8 to 12 bits per pixel. In this example, the low order bits (4 to 8) respectively provide no significant image data. 
     In the present invention, a fast and efficient compression and encoding method is implemented by using unused bits to store a repeat count for repeated values. 
     The most significant N bits of the pixel value are selected where N  300  is the number of significant bits (determined by data analysis or by user selection). If N  300  is less than W  302 , where W is a native machine data type such as 8 bit byte, 16 bit word, or 32 bit double word or some other size for which the computer architecture is optimized, then W-N equals the number of unneeded bits, U  300 . A repeat count, C, can contain a value from 1 to CMAX where CMAX is 2 to the power of U. For example, if U equals 4, C can be a number from 1 to 16. In practice the maximum value will be encoded as a zero because the high order bit is truncated. In the example, decimal 16 has a binary value “10000” will be stored as “0000”. 
     For example, when W is 8, value pairs for N and U could include without limitation (2,6), (3,5), (4,4), (5,3), and (6,2). When W is 16, value pairs for N and U could include without limitation (2,14), (3,13), (4,12), (5,11), (6,10), (7, 9), (8, 8), (9, 7), (10, 6), (11, 5), (12, 4), (13, 3), and (14, 2). When W is 32, value pairs for N and U could include without limitation all combinations of values pairs for N and U where N+U equals 32 and N&gt;1 and U&gt;1. When W is not a multiple of 8, value pairs for N and U could include without limitation all combinations of values pairs for N and U where N+U equals W and N&gt;1 and U&gt;1. 
       FIG. 3A  shows the encoded format where N  300  represent the N most significant bits of the pixel value  299 , U  301  represents the bits that are not used for the data and are used for the repeat count, and W  302  where W is the width of the encoded data and equal to sum of N and U. As stated above W is preferably a native machine element. 
       FIG. 3B  illustrates bit sub-sampling where N&#39;s 300 bit width is 5, U&#39;s 301 bit width is 3, and W  302  is 8. The high order 5 bits  310 - 318  of an 8 bit pixel  325  are extracted to form a five bit sample  330 . The lower 3 bits of  330  are ignored bits  350 . In the formatted code  360 , the ignored bits  350  are replaced with the repeat count value  380 . 
     Encoding 
     The most significant N bits of each pixel are selected from the image to obtain value V. 
     In the encryption embodiment of this invention V may be used to select an encoded value, E, from the encoding table. E is also a N-bit value. The number of elements in the encode table  1100  ( FIG. 11 , shown as an encryption table), is 2 to the Nth power. 
     In the other embodiments of this invention V is used as E. 
     E is saved as the prior value, P. For each subsequent pixel, the encoded value, E, is obtained and compared to the prior value, P. If the prior value, P, is the same as E, then a repeat counter, C, is incremented; otherwise the accumulated repeat count, C, for the prior value, P, is merged with P and placed in an array A that implements the encoded data  140  ( FIG. 1 ) buffer. For example, if W is 8 and N is 4 and C is 10, U is 4, CMAX is 16, and ((P&lt;&lt;U)|C) is the merged value. If the repeat count, C, is greater CMAX, then CMAX is merged with P((P&lt;&lt;U)|CMAX) and placed in the encoded data  140  ( FIG. 1 ) buffer, A. CMAX is subtracted from C and merged values are placed in A until C is less than CMAX. All pixels are processed in this manner until the final value is compressed and encoded. The length, L, of the encoded data  140  ( FIG. 1 ) is also placed in the encoded data  140  buffer. 
     FIG.  4 A 
     Encode Flowchart 
       FIG. 4A  illustrates the encode flowchart  400  which represents the details of the encryption embodiment of the encoding step  130  ( FIG. 1 ) for the present invention. 
     The encoding begins at an encode entry  402 . In an encode initialization step  403 , a prior value P is set to a known value, preferably decimal “255” or hexadecimal 0xFF, a repeat counter C is set to zero, an encoded length L is set to 0, and a completion flag “Done” is set to a logical value of false. Next, a get pixel step  404  obtains a pixel from the image being encoded. At a get value step  405 , a value V is set to the N bit filtered pixel value  299  as derived from the pixel using one of the methods shown in  FIG. 2C to 2G , preferably the fastest as explained above, and extracting the N most significant bits. At a lookup encoded value step  406 , an encoded value E is set to the value of one of the codes  1105  ( FIG. 11A ) of the encode table  1100  as indexed by V. (In the non-encrypted embodiment of this invention, step  406  is bypassed because V is used as E) Next, a “compare previous”  408  decision is made by comparing the values of E and P. If the values are the same, an increment counter step  410  is executed and flow continues to the get pixel step  404  that obtains the next pixel from the image. 
     If the encode value E does not match the prior value P, then a check count overflow  412  decision is made. If the counter C is less than or equal to CMAX, then a new code step  414  is executed, otherwise a counter overflow step  420  is executed. 
     At step  414 , the counter C is masked and bit-wise OR-ed with P shifted left by U bit positions and is placed in the A at the next available location as indexed by the encoded length L. Then, continuing inside flowchart step  414 , L is incremented, the repeat count C is set to 1 and the prior value P is set to E. After step  414 , a “check end of data” decision is made by checking to see if there are any more pixels in the image, and, if not, if the last value has been processed. Because this method utilizes a read ahead technique step  414  must be executed one more time after the end of data is reached to process the last run-length. If there is more data in the image, flow continues to a check of the completion flag “Done” at step  422 . If the check indicates that the process is not completed, flow continues to step  404 . 
     If the end of data is reached but the completion flag “Done” is still false, flow continues to a set done step  418 . At step  418 , the completion flag “Done” is set to logical true, and flow continues to decision  412  where the last run-length will be output and flow will eventually exit through step  414 , decision  416 , decision  422 , and then terminate at encode exit  428 . 
     It is possible for the repeat count C to become larger than CMAX requiring more bits than allocated by this method. This situation is handled by making the “check count overflow”  412  decision and executing the “counter overflow” step  420 . At step  420 , the counter C is masked and bit-wise OR-ed with P shifted left by U bit positions and is placed in the A at the next available location as indexed by the encoded length L. Then, continuing inside flowchart step  414 , L is incremented, and the repeat count C is decrement by CMAX. After step  420 , flow continues to the “check count overflow”  412  decision. Thus when the encode value E repeats more than CMAX times, multiple sets of repeat counts and encoded values are output to the encoded data  140  buffer. 
     This entire process is repeated for each image or video frame selected during optional image sub-sampling (see  110  in  FIG. 1 ) and the encoded length L is transmitted with the encoded data associated with each frame. The encoded length varies from frame to frame depending on the content of the image being encoded. 
     FIG.  4 B 
     Image and Pixel Stream 
       FIG. 4B  illustrates an image and its corresponding stream of pixels. A rectangular image  430  is composed of rows and columns of pixels. The image  430  has a width  440  and a height  450 , both measured in pixels. In this illustrative embodiment, pixels in a row are accessed from left to right. Rows are accessed from top to bottom. Some pixels in the image are labeled from A to Z. Pixel A is the first pixel and pixel Z is the last pixel. Scanning left to right and top to bottom will produce a pixel stream  460 . In the pixel stream  460 , pixels A and B are adjacent. Also pixels N and O are adjacent even though they appear on different rows in the image. If adjacent pixels have the same code the process in  FIG. 4A  will consider them in the same run. 
     Because the video signal being digitized is analog there will be some loss of information in the analog to digital conversion. The video digitizing hardware can be configured to sample the analog data into the image  430  with almost any width  440  and any height  450 . The present invention achieves most of its effective compression by sub-sampling the data image with the width  440  value less than the conventional  640  and the height  450  value less than the convention  480 . In a preferred embodiment of the invention, for use in a medical application with T1 Internet transmission bandwidth, image dimensions are sub-sampled at 320 by 240. However an image dimension sub-sampling resolution of 80 by 60 may be suitable for some video application. 
     FIGS.  5 A to  5 C 
     Run-Length Encoding Formats of the RHN Method 
       FIGS. 5A to 5C  show use of a different structure than the present invention.  FIGS. 5A to 5C  show the formats for the run-length encoding of RHN. In  FIG. 5A , a code byte  500 , with its high order bit designated as a flag bit  510 . 
       FIG. 5B  shows a repeat code  520  comprising a Boolean value one in its flag bit  510  and a 7 bit count  530  in the remaining 7 low order bits. The seven bit count  530  can represent 128 values with a zero representing “128” and 1 through 127 being their own value. 
       FIG. 5C  shows a data code  550  comprising:
         1. a Boolean value zero in its flag bit  510     2. two unused data bits: data bit  6  reference by  565  and data bit  5  reference by  570 , and   3. five bits, data bits  4  to  0 , reference by  575 ,  580 ,  585 ,  590 , and  595 , respectively.       

       FIG. 5C  shows that in every byte of the RHN data code  550  two bits are unused and one bit is used for the flag bit, so that only five of the eight bits are used for data. The remaining three bits are wasted bits  560 . The present invention uses a different structure by placing the repeat count in bits that the RHN format would not have used for data (U). The corresponding ZLN format, ZL5 (where N is 5, U is 3, and W is 8), always uses five bits for data and the remaining 3 bits for the repeat count. In practice, repeat counts are small and often can fit in 3 bits, so this embodiment of the present invention will result in superior compression performance over the RHN method. 
     In addition, the present invention provides for a larger count when the bit filtering is larger. For example, the alternate ZLN format where each byte contains 4 data bits, ZL4 (where N is 4 and U is 4), allows for a four bits of repeat count. For example, in practice, ZL4 is superior to RHN on a typical ultrasound image containing 16 shades of gray. 
     FIGS.  5 D to  5 G 
     Doppler Improvement of ZLN Format 
     The ZLN format for encoding video signals (see for example  FIG. 3A ) has one disadvantage. When the video stream being compressed changes from only grayscale to grayscale overlaid with Doppler enhancement, the colors of the Doppler red and blue scales are also converted to grayscale. A Doppler improvement aspect of the present invention provides a variable means of encoding the Doppler enhanced image with in the data bits of a ZLN format. 
       FIG. 3A  shows the ZLN format comprising N  300  and U  301  that make up a data element with a bit length of W  302 . 
     The Doppler improvement aspect encodes the Doppler values in the N  300  portion of the ZLN format. However the scope of this invention should not be limited to using this technique with ZLN formats only as other compression formats are anticipated by this invention. 
     Doppler Encoding Format 
     The Doppler enhanced grayscale image must be captured as color data (see  FIG. 2B ). If the red, green, and blue values are the same, then the pixel is gray (e.g.  FIG. 2G ). If the red, green, and blue values are not equal, then the pixel is representing a red scale or blue scale value (e.g.  FIG. 2F ). By comparing the values of the red, green, and blue values, a red scale or blue scale value is determined. 
     In  FIG. 5D , two bits, S  503 , are used to indicate which scale the pixel is from. The high bit order bit, S 1   501 , is used to indicate that the value is a gray scale value: zero means grayscale (e.g.  515  in  FIG. 5E and 541  in  FIG. 5F ), one means Doppler (e.g.  525  and  535  in  FIG. 5E ). The low order bit, S 0   502 , is used to indicate red scale or blue scale: zero means red scale (e.g.  525  in  FIG. 5E ), one means blue scale (e.g.  535  in  FIG. 5E ). In the grayscale code  515 , the value of the S 0  bit is a don&#39;t care  512  and it can be coded as either a zero or a one. In combination with the ZLN format, the remaining bits of W are used for a repeat count, C ( FIG. 5G ). 
     An alternate embodiment of this invention uses lookup tables rather selecting the most significant bits. Instead of one encode (e.g.  FIG. 11A ) and one decode table (e.g.  FIG. 11B ) as used in ZLN, a set of tables is used for each scale, gray, red, and blue, respectively.  FIG. 11C  shows an example of a red scale decode table. 
     In an alternate embodiment, S 0  is used as an additional bit of grayscale resolution since S 0   502  is not used in the grayscale case  545  ( FIG. 5F ). 
     In a method where W is the number of bits in a native machine data type, and N is the number of significant grayscale bits, two bits, S  503 , are used to indicate which scale the pixel is from. The high bit order bit S 1   501  is used to indicate that the value is a gray scale value: zero means grayscale  515 , one means Doppler  525  and  535 . The low order bit, S 0   502 , is used to indicate red scale or blue scale: zero means red scale  525 , one means blue scale  535 . In the ZLN combination, the remaining unused bits, U, are used for a repeat count, C, such that W equals 2+N+U ( FIG. 5G ). 
     N bits of the blue component of the pixel value is used to index into a blue encode table to obtain the encoded value, E. In the ZLN method, if E is repeated, a repeat count, C, is incremented. 
     X  557  is a concatenation of S 1 , S 0 , E, and C. 
     In this embodiment, like the ZLN method, the pixels of the frame are processed pixel by pixel as disclosed in reference to  FIGS. 4A and 4B . When a value, E, is not repeated X is placed in the next location in the compression array with a repeat count, C, equal to one. 
     Three decode tables that correspond to the grayscale, red scale, and blue scale encode tables contain the data necessary to reconstruct the original value for the appropriate image. If the target color image format is W*4 bit color ( FIG. 2A ), then the decode table has W bits for alpha  208 , red  206 , green  204 , and blue  202  each, respectively. If the target color image format is W*3 bit color, then the alpha value is not used. If the image is W bit grayscale than only the grayscale value is used to create the decompressed and decoded image. 
     To decode and decompress, the encoded data is processed W bits at a time as X. S 1 , S 0 , E, and C are extracted from X with appropriate masks and shifts. If S 1  is zero indicating grayscale, E is used as an index into the gray scale decode table. If S 1  is one indicating Doppler and S 0  is zero indicating red scale Doppler, E is used as an index into the red scale decode table ( FIG. 11C ). If S 1  is one indicating Doppler and S 0  is one indicating blue scale Doppler, E is used as an index into the blue scale decode table (not shown, but with the proper values in the blue bit column  1126 ). The decoded value is placed into the decoded and decompressed image. Each X is processed in order until the compressed array length, L, has been processed. 
     FIG.  6   
     Encoded Data Stream 
       FIG. 6  shows a series of exemplary decimal values  610  comprising a first value  620  equal to decimal 0, a second value  622  equal to 0, a third value  624  equal to 0, a fourth value  626  equal to 0, a fifth value  628  equal to 0, a sixth value  630  equal to 2, and a seventh value  632  equal to 10. The value of zero is merely exemplary and could be any binary value. After the encoding step  130  ( FIG. 1 ), the corresponding encoded data  140  ( FIG. 1 ) would be compressed down to three bytes of binary code  640  comprising a first byte  650 , a second byte  653 , and a third byte  656  each containing a merged value and count, ( 651 ,  652 ), ( 654 ,  655 ), and ( 657 ,  658 ), respectively. The first data  651  has a binary value of “00000” which equals the exemplary repeated decimal value. The first count  652  has a binary value “101” which equals decimal five representing the run-length of the repeating value in the first five of the decimal values  610 . The second data  654  has a binary value of “00010” which equals the non-repeated decimal value two. The second count  655  has a value of 1. The third data  657  has a binary value of “01010” which equals the non-repeated decimal value ten. The third count  658  has a value of 1. 
     FIG.  7   
     RHN Codes and Encoded Stream 
       FIG. 7  shows the same series of decimal values  610  ( FIG. 6 ) comprising the first value  620  equal to decimal 0, the second value  622  equal to 0, the third value  624  equal to 0, the fourth value  626  equal to 0, the fifth value  628  equal to 0, the sixth value  630  equal to 2, and the seventh value  632  equal to 10. After encoding by RHN, the corresponding encoded data  140  ( FIG. 1 ) would be compressed down to four bytes of RHN binary code  740 . 
     The embodiment of the present invention shown in  FIG. 6  only requires three bytes to encode the same data. In this example, the present invention is 25% better than the RHN format. 
     FIGS.  8 A and  8 B 
     ZLN Formats 
     The ZLN aspect of the present invention provides for variable formats. The values of N  300 , U  301 , and W  302  can be dynamically changed between frames. For ease of communication a format is named with the prefix “ZL” and a digit representing the value of N. For example, “ZL5” refers to a format where bit width of N is equal to 5. There are multiple values of U depending of the W. To also specify the bit width of U a hyphen and a number can be appended. For example, “ZL5-13” represents a format where N=5 and U=13. “ZL5-3” is a common format and may be imprecisely referred to as “ZL5.” 
       FIG. 8A  shows a number of formats with adjacent labels: ZL3  803 , ZL4  804 , ZL5  805 , ZL8  808 , ZL9  809 , and ZL12  812 . Data bits are represented by “D,” and count bits are represented by “C”. 
       FIG. 8B  shows how the most significant 3 bits of each color component ( 216 ,  214 , and  212  of  FIG. 2B ) are extracted and formatted in ZL9-7C format (the “C” append indicates that the color is preserved). With three red bits represented by “R”, three green bits represented “G” and three blue bits represented by “B”. 
     Decoding 
     To decode the compressed array, the decoder has a decode table that corresponds with the encode table. For W*4 bit color pixels, the decode table contains the appropriate alpha, red, green, and blue values. For W*3 bit color pixels, the alpha value is not used. The compressed array is processed W bits at a time as X. The repeat count, C, is extracted from X by masking off the data value (C=X &amp; (((2**N)−1)&lt;&lt;U)). The encoded value, E, is extracted from X by masking off the count (E=X &amp; ((2**U)−1)). The encoded value, E may be used to index into the decryption. The decoded pixels are placed in a reconstructed image and repeated C times. Each element of the compressed array, A, is processed until its entire length, L, has been processed. 
     FIG.  9   
     Decode Flowchart 
       FIG. 9  illustrates the decode flowchart  920  which presents the details of the decryption embodiment of the decode step  160  ( FIG. 1 ) and the image reconstitution step  180  ( FIG. 1 ). 
     The decoding begins at a decode entry  900 . In a “decode initialization” step  901 , a repeat counter C is set to one, an encoded length L is set to the value obtained with the encoded data  140  ( FIG. 1 ), and an index I is set to 0. Next, a “get code” step  902  obtains a signed byte X from the encoded data  140  ( FIG. 1 ) array A. The index I is incremented. The count (for example the 3-bit count  380  as shown in  FIG. 3B ) is extracted from X by masking off the data bits and placed in the repeat counter C (C=X &amp; ((2**N)−1&lt;&lt;U). The value of E is extracted from X by masking off the count bits (E=X &amp; (2**U)−1). In practice, the count mask and value mask can be pre-computed with the following two lines of code in the C programming language: 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 valueMask = −1 &lt;&lt; U; 
               
               
                   
                 countMask = ~valueMask; 
               
               
                   
                   
               
            
           
         
       
     
     In this illustrative decryption embodiment of the present invention, flow goes to a “decode lookup” step  908  where the value of E is used to index into the decode table  1110  ( FIG. 11 , shown as decryption table) to obtain a pixel value V. In the other embodiments where E is not encrypted, E is used as V and step  908  is bypassed. Flow continues to a “check zero count”  909  decision. 
     The  909  decision always fails the first time ensuring that a place pixel step  910  is executed. The place pixel step  910  places the pixel value V in the next location of the decompressed image and decrements the repeat counter C and returns to the  909  decision. The pixel value V is placed repeatedly until C decrements to zero. Then the  909  decision branches flow to a “reset counter” step  914 . At step  914  the repeat counter is reset to 1. 
     Flow continues to the “check length”  916  decision where the index I is compared to the encoded length L to determine if there are more codes to be processed. If I is less than L flow returns to step  902 , otherwise the decode process terminates at a “decode exit”  918 . 
     The entire decode process is repeated for each encoded frame image. 
     FIG.  10   
     Interpolation 
       FIG. 10  illustrates interpolation when two adjacent pixels  1010  and  1012  and two subsequent row adjacent pixels  1014  and  1016  are stretched to insert a new row and column of pixels. 
     Pixels  1052 ,  1054 ,  1056 ,  1058  and  1060  are inserted due to the enlargement of the image. Their values are calculated by averaging the values of the two pixels above and below or to the left or the right of the new pixel. A preferred sequence is calculation of: 
     1.  1052  between  1010  and  1012   
     2.  1054  between  1010  and  1014   
     3.  1058  between  1012  and  1016   
     4.  1056  between  1054  and  1058   
     Pixel  1060  can be calculated on the interpolation for the subsequent row. 
     FIG.  11   
     Encryption 
     By using corresponding encoding and decoding tables the data can be encrypted and decrypted without using actual values. Encryption provides a level of security for the encoded data  140  while in storage or transit. 
       FIG. 11  shows an example of an encryption table  1100 , where N is 3 and W is 8, and a decryption table  1110 , where N is 3 and U is 5. 
     The encode table  1100  is 2 to the power of N in length. If the target color image format is W*4 bit color, then the decode table  1110  has W bits for alpha, red, green, and blue each, respectively. If the target color image format is W*3 bit color, then the alpha value is not used. If the image is W bit grayscale then only the grayscale value is used to create the decompressed and decoded image. 
     The corresponding table elements are mapped to each other. For example, 0 could encode to 22 as long as the 22 nd  element of the decode table returns (0xff&lt;&lt;24|0&lt;&lt;16|0&lt;&lt;8|0). 
     When these versions of the tables are used, the encode and decode processes and their speed of execution are substantially the same but the encoded data  140  ( FIG. 1 ) becomes a cipher and has a higher level of security. It should be recognized by one with ordinarily skill in the art that there are other embodiments of the present invention with different encryption/decryption table rearrangements. 
     FIGS.  12 A through  12 D 
     Compression and Decompression Devices 
       FIGS. 12A and 12B  show devices for compressing and decompressing, respectively, a stream of video frames. 
       FIG. 12A  shows a video signal  1215  being compressed and encoded by a compressor  1210  to form an encoded data stream  1235 , which is sent to an I/O device  1240 . The video signal  1215  comprises a series of video frames  1200 , shown as first video frame  1205   a , second video frame  1205   b , . . . through nth video frame  1205   n . The encoded data stream  1235  comprises a series of encoded data  1220 , shown as first encoded data  1225   a , second encoded data  1225   b , . . . , through nth encoded data  1225   n.    
       FIG. 12B  shows an input encoded data stream  1245  being received from an I/O device  1240 , and then, decoded and decompressed by a decompressor  1250  to form a video sequence  1270 . The input encoded data stream  1245  comprises received encoded data  1238 , shown as first received encoded data  1230   a , second received encoded data  1230   b , through nth received encoded data  1230   n . The video sequence  1270  comprises a series of decoded video frames  1268 , shown as first decoded video frame  1260   a , second decoded video frame  1260   b , . . . , through nth decoded video frame  1260   n.    
       FIG. 12C  shows an embodiment where the I/O device  1240  of  FIGS. 12A and 12B  is a storage medium  1280 . The encoded data stream  1235  from the compressor  1210  is stored in the storage medium  1280 . The storage medium  1280  provides the input encoded data stream  1245  as input to the decompressor  1250 . 
       FIG. 12D  shows an embodiment where the I/O device  1240  of  FIGS. 12A and 12B  is a communications channel  1290 . The encoded data stream  1235  from the compressor  1210  is transmitted over the communications channel  1290 . The communications channel  1290  provides the input encoded data stream  1245  as input to the decompressor  1250 . 
     FIGS.  13 A through  13 J 
     Compressor Details, Encoding Circuit, and Bitwise Pixel Sub-Samplers 
       FIG. 13A  shows details of an embodiment of the compressor  1210 , which comprises a video digitizer  1310 , a video memory  1330 , an encoding circuit  1350 , and encoded data  1370 . Each video frame  1205  in the series of video frames  1200  is digitized by the video digitizer  1310  and stored along path  1320  in the video memory  1330 . The encoding circuit  1350  access the digitized video frame via path  1340  and outputs the encoded data  1370  along path  1360 . The encoded data  1225  corresponding to each video frame  1205  is then output from the compressor  1210 . 
       FIG. 13B  shows further details of an embodiment of the encoding circuit  1350 . A pixel sub-sampler  1380  scans each pixel from the digitized video frame in the video memory  1330 . A pixel index  1332  is used to drive a scan  1331  signal to select each pixel from the video memory, in a predetermined sequence. A novel aspect of the present invention is that the compression method can be accomplished with a single scan of the video memory for each frame. The pixel sub-sampler  1380  selects a predetermined number of bits from each pixel and outputs the data value along path  1385 . Alternatively, the pixel sub-sampler  1380  encodes the sub-sampled data by using a lookup table similar to  FIG. 11A . Different pixel sub-samplers  1380  will be discussed in reference to  FIGS. 13C through 13J . The data/count  1390  unit increments the count each time the output of the pixel sub-sampler  1380  is the same; otherwise, when the output of the pixel sub-sampler  1380  is different (or when the counter reaches the maximum count value, the data and count are combined as a code and output along path  1395  to the encoded data  1225  for the frame currently in the video memory  1330 . The location of the code in the encoded data  1225  is selected by the code index  1392  signal. 
       FIG. 13C  shows further details of a generic pixel sub-sampler  1380 . When a pixel is scanned from video memory along path  1340 , it has an original pixel bit width, P. A pixel extractor  1382  extracts a subset of bits from each pixel with a value bit width, V, along value path  1383 . The value bit width V is less than the pixel bit width P. A coder  1384  takes the V bits from the pixel path  1383  and outputs a code with an encoded bit width, E, as the data value along path  1385 . One embodiment of the coder is a null coder, or pass-through coder. Another embodiment of the coder uses an encryption table to encrypt the data value as an encrypted data value. 
       FIGS. 13D through 13J  show embodiments of pixel sub-samplers. 
       FIG. 13D  illustrates a 24 to 5 bit sub-sampler  1380   a , where the pixel bit width, P, is 24; the value bit width, V, output from the pixel extractor  1382  is 8 (see  FIG. 2H ); and the encoded bit width, E, output from the coder  1384  is 5. In this embodiment, the extracted 8 bits could be any component of the grayscale (e.g.  FIG. 2G ) or the high order 8 bits of the 24-bit value. 
       FIG. 13E  illustrates a 24-bit RGB to 5 bit sub-sampler  1380   b , where the pixel bit width, P, is 24 divided into 8 bits of red, green, and blue (RGB, see  FIG. 2B ); the value bit width, V, output from the pixel extractor  1382  is 8; and the encoded bit width, E, output from the coder  1384  is 5. In this embodiment, the extracted 8 bits could be an average (e.g.  FIG. 2C ) or one of the colors (e.g.  FIG. 2D ,  2 E, or  2 F). 
       FIG. 13F  illustrates a 32-bit RGB to 5 bit sub-sampler  1380   c , where the pixel bit width, P, is 32 divided into 8 bits of red, green, blue, and alpha (see  FIG. 2A ); the value bit width, V, output from the pixel extractor  1382  is 8; and the encoded bit width, E, output from the coder  1384  is 5. In this embodiment, the extracted 8 bits could be an average (e.g.  FIG. 2C ) or one of the colors (e.g.  FIG. 2D ,  2 E, or  2 F). 
       FIG. 13G  illustrates a color 9-bit sub-sampler  1380   d , where the pixel bit width, P, is 24 divided into 8 bits each of red, green, and blue; the value bit width, V, output from the pixel extractors  1382  is 9; and the encoded bit width, E, output from the coder  1384  is 9. In this embodiment, the high order 3 bits of each color component are selected (e.g. ZL9C shown  FIG. 8B ). 
       FIG. 13H  illustrates a YUV sub-sampler  1380   e , where the pixel bit width, P, is 24 divided into 8 bits for each of YUV; the value bit width, V, output from the pixel extractors  1382  is 8; and the encoded bit width, E, output from the coder  1384  is 5. In this embodiment, four bits of the Y value is extracted and 2 bits of each of the U and V values are extracted. This 8 bit value is further coded as a 5 bit value. 
       FIG. 13I  illustrates a 36-bit RGB to 24-bit sub-sampler  1380   f , where the pixel bit width, P, is 36 divided into 12 bits each of red, green, and blue; the value bit width, V, output from the pixel extractors  1382  is 24; and the encoded bit width, E, output from the coder  1384  is also 24. In this embodiment, the high order 8 bits of each 12-bit color component are selected. 
       FIG. 13J  illustrates a 15-bit sub-sampler  1380   g , where the pixel bit width, P, is 24 divided into 8 bits from each color component; the value bit width, V, output from the pixel extractor  1382  is 15; and the encoded bit width, E, output from the coder  1384  is 15. In this embodiment, the high order 5 bits of each 8-bit color component are selected. 
     FIGS.  14 A through  14 C 
     Variable Selection of Bit-Wise Sub-Sampling 
       FIGS. 14A through 14C  show embodiments of a device for variably altering the number of bits. 
       FIG. 14A  illustrates 24-bit to variable bit sub-sampler  1400 . When a pixel is scanned from video memory along path  1340 , it has an original pixel bit width, P, equal to 24 bits. These 24 bits are passed as input to a number of sub-samplers. The variable number of bits is selected by a number of bits selector  1410  as indicated by a number of bits indicator  1420  and outputs a code with an variable encoded bit width, E, as the data value along path  1385 . A user at remote receiver  1610  sets the number of bits indicator  1420  (see discussion regarding  FIGS. 16A and 16B ). The variable bit sub-sampler comprises a generic 3-bit sub-sampler  1401 , a generic 4-bit sub-sampler  1402 , generic 8-bit sub-sampler  1403 , and generic 10-bit sub-sampler  1404  which are embodiments of the generic sub-sampler shown in  FIG. 13C  with specific values for E. The variable bit sub-sampler further comprises nested sub-samplers: the 24 to 5 bit sub-sampler  1380   a  of  FIG. 13D , the  1380   d  of  FIG. 13G , and the 15-bit sub-sampler  1380   g  of  FIG. 13J . This is illustrative of the types of bit sub-samplers that can be variably selected. 
     Likewise,  FIG. 14B  illustrates a 36-bit to variable bit sub-sampler  1430 , where P is 36 and the number of bit that can be selected are 12, 15, or 24, respectively. 
       FIG. 14C  shows that the 24-bit to variable bit sub-sampler  1400  of  FIG. 14A  and the 36-bit to variable bit sub-sampler  1430  of  FIG. 14B  can be further combined to form at 24/36 bit variable bit sub-sampler  1440  where a second selector  1450  is used to selected either the 24 bit inputs or the 36 bit inputs using selection logic  1460  that also receives the number of bits indicator  1420 . A selection signal  1470  enables either the output of 24-bit to variable bit sub-sampler  1400  or the output of 36-bit to variable bit sub-sampler  1430 . Sub-samplers  1400  and  1430  both receive the number of bits indicator  1420  as shown in  FIG. 14A  and  FIG. 14B . In this way any number of bits may reasonably be selected from either a 36 or 24-bit pixel bit width. 
     FIG.  15   
     Decompressor Elements 
       FIG. 15  shows details of an embodiment of the decompressor  1250 , which comprises a decoding circuit  1510  which inputs received encoded data  1230  and outputs decoded pixel values  1520  to an image memory  1540 . A decoder pixel index  1530  selects the location in the image memory  1540  to store the decoded pixels values  1520 . The image memory  1540  delivers each decoded video frame  1260  to the video display. 
     FIGS.  16 A and  16 B 
     Parameters Altered by a Remote Receiver 
       FIG. 16A  shows a system for setting width, height, frame rate, brightness, and contrast in a transmitter  1600  which are variably altered by a receiver  1610 . The receiver sends commands to the transmitter  1600  via setting control path  1615 . The commands alter the transmitter settings  1660 . 
     The settings  1660  include brightness  1661 , contrast  1662 , height  1663 , width  1664 , and frame rate  1665 . The brightness  1661 , contrast  1662 , height  1663 , and width  1664  setting alter the attributes of each frame as it is digitized in a frame sub-sampler  1620 . The brightness  1661  and contrast  1662  settings alter the video digitizer  1310  ( FIG. 13A ) as it senses the video frame. The height  1663  and  1664  allow for optionally selecting a subset area of each frame; this is area sub-sampling. Alternatively, height  1663  and  1664  allow for optionally selecting a subset of pixels from an array of pixels that make up a single frame, by skipping pixels in a row or by skipping rows; this is image sub-sampling. The frame rate  1665  setting alters the frame selector  1670  which drives the frame select indicator  1675  to optionally sub-sample frames from a sequence of video frames; this is frame sub-sampling. 
     The frame sub-sampler  1620  outputs a selected frame  1630  along path  1621 . The transmitter pixel sub-sampler  1640  scans the selected frame  1630  getting each pixel from frame  1632  and outputs data values along path  1642  to a run length encoder  1650 . The encoded data stream  1235  is then transmitted to the remote receiver  1610 . 
       FIG. 16B  shows additional elements of a system for setting the number of pixel bits in an alternate transmitter  1690  which is variably altered by a receiver  1610 . The receiver sends commands to the transmitter  1600  via setting control path  1615 . The commands alter the transmitter settings  1660 . The settings include a number of pixel bits setting  1680  which affect the number of bits selected by the transmitter pixel sub-sampler  1640 . The pixel sub-sampler  1640  could be any pixel sub-sampler, for example, see  FIG. 13C through 13J  and  14 A through  14 C. The transmitter pixel sub-sampler  1640  scans the selected frame  1630  (as in  FIG. 16A ) getting each pixel from frame  1632  and outputs data values along path  1642  to a run length encoder  1650 . The encoded data stream  1235  is then transmitted to the remote receiver  1610 . 
     These embodiments illustrate the novel feature of the present invention of allowing a user at a remote receiver  1610  to control aspects of the transmitter  1600  or  1690  from a remote location, including brightness, contrast, frame dimensions, frame rate, image area, and the type of compression used. 
     FIG.  17   
     Further Lossless Compression Step 
       FIG. 17  shows a lossless compression step for further compressing an encoded data buffer. After a run-length encoding step  1700  in the transmitter, a run-length encoded output  1710  can be further processed with a further lossless compression step  1720  resulting in further lossless compression output  1730 . The further lossless compression step  1720  could be implemented as a variable length coding, arithmetic coding, or other compression step known in the art. 
     FIG.  18   
     Image Stretching 
       FIG. 18  shows images being enlarged by stretching. An unstretched frame  1800  is stretched during stretching step  1820  resulting in an enlarged image  1810 . When a frame is image sub-sampled or area sub-sampled, the remaining data can be stretched to fill the full display area on the receiver  1610 . This results in an interpolated image or magnified image, respectively. 
     Distinguishable Characteristics 
     Most video images contain regions that are distinguishable from the other pixels that make up an image. Sometimes the distinguishing characteristic is the importance of the region to the viewer. In medical imaging such as ultrasound, the generated image in the center of the display may be of most importance to the viewer. Sometimes the distinguishing characteristic is the compressibility of the regions. Sometimes the distinguishing characteristic is the color depth of the regions. Sometimes the distinguishing characteristic is the rate of change of the regions. 
     A region of solid color or grayscale value compresses more efficiently than a series of varying values. This is true of the ZLN compression method. If the regions are distinguished based on their compressibility, different compression methods can be applied to each region. 
     Grayscale pixel values can be stored in 8 bits while the corresponding quality of color pixel is often stored in 24 or 32 bits. If the regions are distinguished based on their storage requirements (also known as color depth, or bit depth), a significant space or bandwidth saving can be made. 
     A Doppler enhanced image such as a weather map or an ultrasound medical image is synthesized by the Doppler circuitry. In the case of a weather map, the underlying image does not change but the Doppler enhanced velocity scales do change from frame to frame. In the case of Doppler enhanced ultrasound image, the underlying grayscale ultrasound image changes more frequently than the circuitry can calculate and display the Doppler information. If the Doppler and non-Doppler regions are processed separately the overall effective compression sizes and transmission times can be reduced. 
     Automatic Switching between Grayscale Only and Doppler Enhanced Formats 
     As disclosed, for example in U.S. application Ser. No. 09/321,922 regarding its FIG. 2, the video image capture device receives a stream of video images ( 1200 ) from a video source. The compressor  1210  is configured to compress the stream of video images  1200  thereby creating a compressed stream of video images (e.g.  1235 ). This is also shown in  FIG. 12C . Video parameters such as the compression algorithm are included within the video settings. In one embodiment of this invention, the compressor, which is determining the scale of each pixel, can count the number of Doppler enhanced pixels in each frame, or image, of the video stream. As discussed above, whether a pixel is grayscale or Doppler enhanced is determined by comparing the red, green, and blue component values. If no Doppler pixel is found in an image, a standard grayscale format, such as ZLN format, can be used as the compression method of the compressor (i.e. Doppler enhanced encoding can be automatically switched off). When a Doppler enhanced pixel is found in a subsequent frame of the video stream by the same counting mechanism, the compressor can automatically be switched to use the Doppler enhanced format described above. The compressor will continue to use this compression method until the counting mechanism fails to detect a Doppler enhanced pixel, then the grayscale only compression method can be switched on again. 
     ADVANTAGES 
     Noise Filtering and Image Enhancement 
     The removal of the least significant bits of pixel values results in high quality decompressed images when the original image is generated by an electronic sensing device, such as an ultrasound machine, which is generating only a certain number of bits of grayscale resolution. By variably altering the number of most significant bits, various filters can be implemented to enhance the image quality. Such a noise filter can be beneficial when the image is generated by an imaging technology such as radar, ultrasound, x-ray, magnetic resonance, or similar technology. Variations can be made to enhance the perceived quality of the decompressed image. Therefore, altering the number of data bits selected and altering the width of the repeat count is anticipated by this invention and specific values in the examples should not be construed as limiting the scope of this invention. 
     Dynamic Variable Formats 
     While a video stream is being viewed, a viewer on the decoding end of the transmission can vary the settings for the compressor. Different tradeoffs between image spatial and temporal quality can be made. As the contents of the video signal change an appropriate format can be selected. Control signals can be sent back to the compressor via a communications link. 
     While a video stream containing Doppler enhancement is being viewed, a viewer on the decoding end of the transmission can vary the settings for the compressor. Different tradeoffs can be made. For example, more Doppler detail can be chosen with slower frame rate. 
     Automatic Switching 
     If no Doppler pixel is found in an image, a standard ZLN format can be used (i.e. Doppler enhanced encoding can be automatically switched off). When Doppler enhancement again appears in the video stream (as recognized by the detection of a Doppler pixel in a frame), the Doppler enhanced encoding can automatically be switched on again. 
     Execution Speed 
     The preferred embodiment of this invention uses a number of techniques to reduce the time required to compress and decompress the data. 
     The methods require only a single sequential pass through the data. Both the compression steps  100  and the decompression steps  150  access a pixel once and perform all calculations. 
     When selecting the filtered pixel value  299 , the preferred embodiment selects the low order byte from the 32 bit pixel value  200  or the 24 bit pixel value  210  so that an additional shift operation or addressing operation is avoided. 
     The shift operation is a fast and efficient way to convert a byte or word to the filtered pixel value  299 . 
     General Purpose 
     The lossless compression of the sampled data achieved by a preferred embodiment of the present invention results in high quality video streams that have general purpose application in a number of areas including, without limitation, medical, aviation, weather traffic, video conferencing, surveillance, manufacturing, rich media advertising, and other forms of video transmission, storage, and processing. 
     Lossless Nature/No Artifacts 
     Once the analog signal is sub-sampled and filtered to select a filtered pixel value that eliminates some of the real world defects, the methods of the present invention compress and decompress the data with no irreversible data loss. Unlike JPEG and MPEG, the decompressed image never suffers from artificially induced blocking or smearing or other artifacts that are result of the lossy compression algorithm itself. As a result even a small sub-sample of the image remains clear and true to the perceived quality of the original image. 
     Superior Features over RHN Format 
     When compared against the RHN format, the format and methods of the present invention provide a number of advantages, including, but not limited to, faster speed and smaller size of encoded data, better performance for both medical and typical video images, and a typically closer representation of the original video signal. 
     Superior Features over ZLN Format 
     When compared against the ZLN format, the format and methods of the Doppler improvement aspect of the present invention provide a number of advantages, including, but not limited to, a typically closer representation of the original video signal. As stated above, when compared to a method using all three or four color components, the Doppler improvement aspect of the present invention provides the advantages of efficient encoding of Doppler enhanced images and reduced size of an encoded data buffer that contains Doppler enhancement. 
     Optimal Encoding 
     The present invention also provides a method for separating a video image into distinguishable regions. Each region can be encoded, compressed, and transferred in a manner that is optimal for its distinguishing characteristics. 
     Reduced Size 
     The present invention may also reduce the size of an encoded video stream. The reduced size saves in the usage and cost of storage devices and computing and networking resources. 
     Reduced Bandwidth 
     The present invention may also reduce the bandwidth required to transfer a compressed video stream. Both transfers within a computer system to a storage device, such as a hard disk, tape drive, and the like, and transfers between a transmitter and a receiver over a network, such as a LAN, the Internet, a television network, and the like, are improved. 
     This improved bandwidth allows for the regions of interest to be displayed at a higher quality of resolution and motion while reducing the requirements and cost of a high bandwidth connection or a connection with reduced traffic. For example, the present invention allows a video steam that previously had to be sent over a 1.54 Mb T1 line to be sent over a much less costly and much more prevalent DSL, cable modem, or 56 Kb modem connection. 
     Efficient Doppler Handling 
     The present invention also provides efficient methods for handling Doppler enhanced images. This allows for lower cost storage of weather, air traffic, and medical images. It also allows for enhanced quality of images. 
     CONCLUSION, RAMIFICATION, AND SCOPE 
     Accordingly, the reader will see that the compression and decompression steps of the present invention provide a means of digitally compressing a video signal in real time, a means of digitally compressing Doppler enhanced video signal in real time, communicating the encoded data stream over a transmission channel, and decoding each frame and displaying the decompressed video frames in real time. 
     Furthermore, the present invention has additional advantages in that:
     1. it provides a means of filtering real world defects from the video image and enhancing the image quality;   2. it allows for execution of both the compression and decompression steps using software running on commonly available computers without special compression or decompression hardware;   3. it provides decompressed images that have high spatial quality that are not distorted by artifacts of the compression algorithms being used;   4. it provides a variably scalable means of video compression and of adding Doppler enhancement; and   5. it provides a means for reducing the space required in a storage medium.   

     While my above descriptions contain several specifics these should not be construed as limitations on the scope of the invention, but rather as examples of some of the preferred embodiments thereof. Many other variations are possible. For example, bit ordering can be altered and the same relative operation, relative performance, and relative perceived image quality will result. Also, these processes can each be implemented as a hardware apparatus that will improve the performance significantly. In another example, frame differencing may be applied to the input stream to select a subset of a frame to be the original image, or a post processing step could be added to remove artifacts introduced by a particular decompression method. 
     Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.