Abstract:
An improved method and apparatus for scanning of anamorphic film utilizes increased number of scans and combination of scan lines for video output generation. A progressive raster scan is made of the film and stored in a frame memory. The spacing between the scan lines is made smaller than for the conventional scanning of an anamorphic image. In the preferred embodiment, the spacing between the scan lines for a 2:1 anamorphic image equals the spacing for scanning of a non-anamorphic image. The scan lines are retrieved from the memory and combined, preferably with the two nearest neighbors of the scan line. Optionally, the combined lines are weighted, preferably with the center scan line having larger weight. Subsequent video output lines are formed by repeating the process. Progressive video output or interlace output is provided as desired.

Description:
FIELD OF THE INVENTION 
     This invention relates to the conversion of images from film to an electronic format. More particularly, it relates to the telecine scanning of film recorded in an anamorphic format. 
     BACKGROUND OF THE INVENTION 
     Images are often shot on photographic film. The images may be displayed from the film, such as direct projection of motion picture film in a theater. Also, images on film are converted from film to an electronic medium, such as videotape, which is then used for mass distribution or broadcast via television or cable. 
     Conventionally, motion picture film is converted to an electronic medium by a telecine. The most widely available telecines utilize a flying spot scanner to scan each image of the film. As shown in  FIG. 1  and  FIG. 2 , movie film  10  is scanned in a raster pattern  12 . Light from a CRT  14  is focused via lenses  16  onto one or more photo cells  18  after having passed through the film  10 . The output of the photo cell  18  constitutes an electronic signal whose intensity corresponds to the progressive scan of the movie film  10 . Optionally, a color corrector  20  may vary the electronic signal of the colors as is known in the art. Ordinarily, the output of the telecine is stored in memory. Conventionally, a frame store memory  22  stores a digital version of the image. As necessary, an analog to digital converter  24  is used if the output of the telecine or color corrector is analog. 
     Current television displays use an interlaced display system. A first field for display on a television will utilize the first, third, fifth and so on, scans from the raster  12 , and the second field will use the second, fourth, sixth and so on lines of the raster  12 . By storing the progressive scan from the telecine in the frame store memory  22 , the interlaced output may be achieved by sequentially addressing the memory  22  for the desired lines. The output from the memory  22  may be either digital video output  26  or, after passing through a digital to analog converter  28 , an analog video output  30 . The write address generator  32  for the memory  22  generally will sequentially record the raster scan  12 . The read address generator  34  will read data from memory  22  in the selected format, such as the interlaced format. 
     In motion pictures, the aspect ratio (that is, the ratio of the width to the height of the image) is larger than for most current television sets. Motion pictures are often shot in cinemascope format which has an aspect ratio of 2.35:1. Conventional television sets have an aspect ratio of 1.33:1 (4/3). When shooting motion picture film, a special 2:1 anamorphic lens is often used to compress the image onto conventional sized film. Such a 2:1 anamorphic lens results in a 1.175 aspect ratio. Inspection of the film shows images which are squeezed by a factor of 2:1. By way of example, people appear very tall and very thin. When anamorphic film is replayed in the theater, a projection lens expands the picture to the correct proportions. 
     When a telecine is used to scan ordinary film for a 1.33:1 aspect ratio, the scan is as shown in  FIG. 3   a . While literally hundreds of lines are used to scan a single image on a film, for simplicity the image in  FIG. 3   a  shows 28 lines. A scan of film for use in a 1.33:1 aspect ratio display would use lines  1 - 20  written to the memory  22 . As each sequential line is scanned, it is stored in memory  22  at the write address specified by write address generator  32 . Extra CRT scan lines are typically present, and are shown above and below scan lines  1 - 20 . 
     Telecines ordinarily, do not utilize an anamorphic lens. Thus, when scanning images recorded with an anamorphic lens, some correction must be made, lest the images appear in their squeezed form. The conventional solution has been to double the vertical raster height of the flying spot scanner  8 .  FIG. 3   b  shows the raster scan when expanded by 2:1 in the vertical direction. When scanning an image area of cinemascope film having a 1.18:1 aspect ratio, lines  5 - 16  (shown bracketed) would be used. By doubling the scan distance, the image is converted back to its normal proportions. However, when the scanned image is then displayed on a television having a 1.33:1 aspect ratio, the image fills only a portion of the screen  40  ( FIG. 4 ). The portions outside the image area  42  are blanked, and appear black. This display is known as a “letterbox” display. 
       FIG. 3   c  shows the video output from the memory for the letterbox format. Lines  1 - 4  and  17 - 20  will be blanked. For output in the interlaced format, lines  5 ,  7 ,  9 , and so on would be output in the first frame, and lines  6 ,  8 ,  10  and so on would be output in the second frame. 
     There have been long standing and vexing problems to the image quality utilizing the above described technique and apparatus. The first problem is that a moire pattern, that is, the type of image often seen when two geometrically regular patterns (as when two sets of parallel lines are superimposed especially at an acute angle) may show up on the video image. This is especially pronounced where numerous horizontal lines are shown in the image, bleachers, car grills or certain fabrics. By way of example, as a image pans across bleachers, a moire pattern may travel over the bleachers, clearly creating an image which would not be observed by someone at the actual scene. This lack of realistic representation on video has been a serious problem. 
     The second problem occurs if the scanning spacing on the telecine matches a spacing on the image. In this event, when an interlaced display is utilized, the image visibly flickers. To consider an extreme example, if the image consisted of alternating horizontal black lines on a white background, and if the telecine scan were such that the odd numbered raster scans were all black and the even numbered raster scans were all white, when played back, because of interlacing, the image would be alternately all black and all white, causing a serious flicker problem. 
     Yet a third problem resulting from the scanning method utilized in the prior art is that the image quality of the video is visibly degraded. This results from the use of a twice as wide scan, wherein substantial detail may be omitted from the image. 
     Despite the long standing and vexing nature of these problems, no satisfactory solution has been proposed heretofore. 
     SUMMARY OF THE INVENTION 
     An improved method and apparatus for converting anamorphic images to electronic format is provided. The film image is scanned with a progressive raster scan and stored in memory as scan lines. The spacing between progressive scan lines is made smaller than that for conventional anamorphic scanning. When scanning two-toone anamorphic film, the spacing is equal to that used for non-anamorphic film. 
     Next, the various scan lines are combined from memory with one or more scan lines, preferably adjacent scan lines. In the preferred embodiment, three horizontal lines are combined. The contribution of the various lines may be either with substantially equal weighing (⅓, ⅓, ⅓) or where there is more weighing given to one line versus another (e.g., ¼, ½, ¼). The subsequent video output line is formed by combining a main scan line separated from the prior scan line by more than one scan line. In the preferred embodiment, the main scan lines are separated by three intermediary lines, resulting in a separation of 4. 
     It is a principal object of this invention to reduce or eliminate moire patterns on video. 
     It is yet a further object of this invention to reduce or eliminate flicker on video. 
     It is yet another object of this invention to provide for improved conversion of cinemascope film to video. 
     It is yet a further object of this invention to provide for improved resolution in the image of a video display formed from an anamorphic film image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a conventional telecine and frame store memory. 
         FIG. 2  is a plan view of film and a frame store memory. 
         FIG. 3   a  is a plan view of a raster scan at a conventional scan rate. 
         FIG. 3   b  is a raster scan having an expanded vertical spacing. 
         FIG. 3   c  shows the display for a monitor. 
         FIG. 4  is a perspective drawing of a monitor showing an image in letterbox format. 
         FIG. 5   a  shows a scan of an image. 
         FIG. 5   b  shows a scan for an image having a 1.18:1 aspect ratio. 
         FIG. 5   c  shows a display for a monitor. 
         FIG. 6  is a block diagram of the digital video frame store of this invention. 
         FIG. 7  is a block functional diagram of the write address generator. 
         FIG. 8  is a functional block diagram of the read address generator. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 5   a ,  5   b  and  5   c  demonstrate the improved method of this invention.  FIG. 5   a  shows the normal raster scan, as described previously in connection  FIG. 3   a . The memory write lines  50  are shown diagrammatically to the left of the raster scan  52 . For an image in the 1.33:1 aspect ratio, lines  1 - 20  of the memory write lines  50  are utilized. For a image having a 1.18:1 aspect ratio additional lines are utilized as shown. Again, the number of lines actually used is in the hundreds, the images in  FIGS. 5   a ,  5   b  and  5   c  using a smaller number of scan lines for clarity. 
       FIG. 5   b  shows the scan for the improved method of this invention. Memory write lines  50  are utilized for all of the image area for the 1.18:1 aspect ratio image. As the raster scan is generated, the information is stored in the frame store memory for later read out. In the preferred embodiment, the spacing between the scan lines in  FIG. 5   b  is one-half the spacing in  FIG. 3   b . It will be appreciated by those skilled in the art that the spacing of  FIG. 5   b  is that which is normally used in scanning a non-anamorphic image. Generally, in accordance with the invention, the spacing between the raster scan lines is made smaller than the spacing between raster scan lines in current anamorphic film scanning. While the spacing is preferably one-half that used in non-anamorphic scanning, the number may be any number smaller than the non-anamorphic spacing. For example, even when scanning 2:1 anamorphic film, it may be desirable to increase the number of scan lines, e.g., to a spacing of one-quarter of the non-amamorphic spacing. In another example, if the anamorphic ratio is other than 2:1, the spacing may be made smaller than the non-amamorphic spacing. 
       FIG. 5   c  shows the read memory lines  54  for the letterbox picture format. For display on a monitor  40  ( FIG. 4 ) having a 1.33:1 aspect ratio, the lines  56  above the image  42  in the letterbox format would be blanked. Similarly, the lines  58  below the image  42  in the letterbox format would be blanked. The unblanked lines are called active scan lines. The video output of active scan lines may be found in multiple fields, such as in an interlaced output where two fields are used. 
     In accordance with the invention, the scanned image stored in the memory is read out and combined with one or more raster scan lines. In the preferred embodiment, three lines are combined, most preferably for a given scan line the nearest neighbor scan lines. However, nearby lines may be combined, and the nearest neighbors ignored, or given a low weighting. 
       FIG. 5   c  provides an example of this most favored format. The memory read lines  54  are shown to the left of the read out image  60 . The first line read out  62  is composed of the scans at memory write line  50  numbers  1 ,  2  and  3 . If the display is assumed to be interlaced, the next read out line  64  would be composed from memory lines  5 ,  6  and  7 . This would be repeated for the display, generally following the pattern of going four lines down in memory (the first factor of two for the anamorphic correction and the second factor of two for interlaced format) until the end of the image is reached. Continuing to assume the interlaced format, the second TV field in the picture area would be composed from lines  3 ,  4  and  5  from the memory. The second line of the image would be composed from lines  7 ,  8  and  9  of memory read lines  54 . This image formation would continue throughout the image area of the memory. After the second TV field was completed, the read out would begin again with the line  62  consisting of memory read lines  1 ,  2  and  3 . 
     The weighing associated with each of the memory lines may be varied at the users discretion. In one preferred mode, the contributions from the lines may be substantially the same, that is, ⅓, ⅓ and ⅓. Alternately, one of the lines may be given preferential weighting, such as in the case where the adjacent lines are sequentially assigned weights of ¼, ½ and ¼. The weights may be changed as desired to produce an optimum image. 
     Further, while demonstrated with the use of adjacent lines, the technique is readily usable with the combining of two or more lines. Any desired weighing of the various lines may then be utilized to optimize the image. 
       FIG. 6  shows a functional block diagram of the preferred embodiment of hardware for the system. Input  60  receives the digital image from the flying spot scanner  8  and optional color corrector  20  and analog to digital converter  24 , as necessary. Frame store memory  62  stores the information received from input  60 . The frame memory  62  may comprise any known type of memory. In the preferred embodiment, this memory may be dynamic random access memory (DRAM) or video random access memory (VRAM), field serial access memory (FSAM) or static random access memory (SRAM). One or more memory may be used as desired. In the preferred embodiment, a multiple frame memory  62  is utilized. If three lines of memory are to be combined, typically three separate memories  62  would be utilized. 
     A memory controller  64  supplies memory write and memory read addresses to the frame memory  62 . The output of the frame memory  62  comprises a main line output  68 , a previous line output  66  and a next line output  70 . In the example of  FIG. 5   c , the first read out line would be composed of memory read lines  1 ,  2  and  3 . The multiplier coefficients are chosen by selector  78 . If in the off position, the output  82  is composed exclusively of the main line output  68 . When in position  1 , the main line output is weighted ½, with the previously line output  66  and next line output  70  being weighted at ¼. The weighted outputs are combined in the summing block  80  and provided as output  82 . When the multiplier coefficient selector  78  is in position number  2  the leading coefficients are ⅓, ⅓ and ⅓. As described above, the coefficients may be chosen as desired, and need not be in these proportions. All of the multiplication, summing and provision of multiplier coefficient  78  may be implemented via known processing techniques through the use of multipliers, summers and microprocessors. 
       FIG. 7  shows a functional block diagram of the write address generator for the memory controller  64 . A horizontal input counter  84  addresses each horizontal pixel position or each group of pixels. By way of example, there may be 16 pixels per horizontal address. A vertical input counter  86  addresses each active line in the progressive scanned raster of the flying spot scanner. Multiplier  88  is used to multiply the number of horizontal addresses in one line times the vertical line number. Summer  90  combines the output of the horizontal input counter  84  and the multiplier  88  to form the memory write address  92 . When the invention is used in the cinemascope mode, there are more active lines in the progressive scan than in the normal scan for a image in the 1.33:1 aspect ratio. 
       FIG. 8  shows a functional block diagram for hardware for the read address generator portion of the memory controller  64 . The memory read address  124  is utilized to address the frame memory  62 . Generally, the horizontal output counter  100  outputs the horizontal position number. This address may refer to each horizontal pixel position, or to a group of pixels, for example 16 pixels per horizontal address. The vertical output counter  102  addresses each active line in one field of an interlaced output raster. The vertical line number output from the counter  102  is multiplied  104  by 2 to perform the interlace function. In the event that an even output field is to be generated, the zero is added to the output of multiplier  104  in summing unit  106 . In the event that an odd output field is to be formed, a 1 is added to the output of multiplier  104  in summing unit  106 . The output of the summing unit  106  is provided to multiplier  108 . The multiplier corrects for the anamorphic compression of the image. For example, the multiplier  108  is set to a factor of 2 if the original image was shot with a 2:1 anamorphic lens. Selector  110  is set in the up position for a normal image having a 1.33:1 aspect ratio, and down to receive the output of multiplier  108  for correction of an anamorphic image. The output of selector  110  is fed to multiplier  112  which multiplies by a factor equal to the number of horizontal addresses in one line. Summing unit  114  combines the output of multiplier  112  with the horizontal position number. Selector  118  is set to specify whether the addresses are for the main line output  68 , the previous line output  66  or the next line output  70 . If the previous line output  66  is desired, the input  116  consisting of the number of horizontal addresses in one line is converted to a negative number and provided to summing unit  120 . The output of summing unit  114  is combined with the output of selector  118  to provide the memory read address  124 . 
     The memory read address output  124  is provided to the frame memory  62 . Generally, the memory will have three simultaneous outputs. This can be achieved with a memory device that has multiple output ports, or alternatively, by three successive reads from the memory  62  with three different read addresses. The data that is read out from the memory  62  can be placed in temporary holding registers until the three reads are complete, at which time the three outputs can be updated simultaneously. 
     Generally, conventional single port memory devices are slower than required to perform all required read and write cycles in the time required. By reading and writing a group of horizontally adjacent pixels in parallel, for example 16 pixels, they may be placed in temporary registers, and when all three reads are complete and it is time to output pixels, the data in these temporary registers may be transferred simultaneously to 16 bit long shift registers. The shift registers then shift the pixel data out one pixel at a time. Through this method, there is 16 times the amount of time to perform a read or write memory cycle. 
     Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims.