PRINT ENGINE/CONTROLLER WITH COLOR MASK

Abstract: A print engine/controller (10) to drive an ink drop print head has an interface (22) at which to receive compressed page data, decoders (28, 88) to decode respective types of image planes in the received compressed page data, and a half-toner/compositor to (29) composite image plane data, the half-toner/compositor including a dot merger unit (58) taking bits from the respective planes as inputs and a color mask register (61) holding masking bits in number equal to the number of image planes, respective input bits to the dot merger unit being ANDed with respective color mask register bits and the resultant bits Ored together to form an output bit in a channel for which there is an ink at the print head. The respective planes to the dot merger unit may include three contone color planes and a high resolution spot plane, and the color mask register is loaded with bits that are selected to place the high resolution spot plane into any one of the respective color channels at the print head. A fixative channel may be generated from any one or more of the respective planes and selected by what bits are loaded to the color mask register. The respective planes to the dot merger unit (58) may include three contone color planes and a bi-level spot plane and the color mask register (61) may be loaded with bits that are selected to split a K plane into C, M, and Y channels for output to a print head without K.

Description: PRINT ENGINE/CONTROLLER WITH COLOR MASK FIELD OF THE INVENTION The invention relates to a print engine/controller (PEC) able to receive print data and generate and output in a format suited to what inks are available at the print head BACKGROUND OF THE INVENTION A range of printer types have evolved wherein an image is constructed from ink selectively applied to a page in dot format In US patent number 6045710 titled 'Self-aligned construction and manufacturing process for monolithic print heads' to the inventor Kia Silverbrook there is set out an assessment of the prior art to drop on demand printers along with its particular manufacturing process A microelectomechanical drop on demand print head hereafter referred to as a Memjet print head has been described in co-pending United States Patent Applications filed simultaneously to the present application and hereby incorporated by cross reference PCT Application Number Docket Number PCT/AU00/00591 MJ62 PC1 /AU00/00578 IJ52 PCT/AUOO/00579 IJM52 PCT/AU00/00592 MJ63 PCT/AU00/00590 MJ58 The Memjet print head is developed from print head segments that are capable of producing, for example, 1600 dpi bi-level dots of liquid ink across the full width of a page Dots are easily produced in isolation, allowing dispersed-dot dithering to be exploited to its fullest Color planes might be printed in perfect registration, allowing ideal dot-on-dot printing The print head enables high-speed printing using microelectromechanical ink drop technology Various methods, systems and apparatus relating to the present invention are disclosed in the following co- pending applications filed by the applicant or assignee of the present invention simultaneously with the present application PCT/AU00/00518, PCT/AU00/00519, PCT/AU00/00520, PCT/AU00/00521 , PCT/AU00/00522, PCT/AU00/00523, PCT/AU00/00524, PCT/AUOO/00525, PCT/AU00/00526, PCT/AU00/00527, PCT/AUOO/00528, PCT/AU00/00529, PCT/AU00/00530, PCT/AU00/00531, PCT/AUOO/00532, PCT/AU00/00533, PCT/AUOO/00534, PCT/AU00/00535, PCT/AUOO/00536, PCT/AUOO/00537, PCT/AU00/00538, PCT/AU00/00539, PCT/AU00/00540, PCT/AU00/00541 , PCT/AU00/00542, PCT/AU00/00543, PCT/AU00/00544, PCT/AUOO/00545, PCT/AUOO/00547, PCT/AU00/00546, PCT/AU00/00554, PCT/AU00/00556, PCT/AU00/00557, PCT/AUOO/00558, PCT/AUOO/00559, PCT/AU00/00560, PCT/AUOO/00561, PCT/AU00/00562, PCT/AUOO/00563, PCT/AU00/00564, PCT/AU00/00565, PCT/AU00/00566, PCT/AU00/00567, PCT/AU00/00568, PCT/AU00/00569, PCT/AUOO/00570, PCT/AU00/00571, PCT/AU00/00572, PCT/AUOO/00573, PCT/AU00/00574, PC I7AU00/00575, PCT/AU00/00576, PCT/AUOO/00577, PCT/AU00/00578, PCT/AUOO/00579, PCT/AUOO/00581, PCT/AU00/00580, PCT/AUOO/00582, PCT/AU00/00587, PCT/AUOO/00588, PCT/AU00/00589, PCT/AU00/00583, PCT/AU00/00593, PCT/AU00/00590, PCT/AU00/00591 , PCT/AU00/00592, PCT/AU00/00584, PCT/AU00/00585, PCT/AU00/00586, PCT/AU00/00594, PCT/AU00/00595, PCT/AU00/00596, PCT/AU00/00597, PCT/AU00/00598, PCT/AU00/00516, PCT/AU00/00517, PCT/AU00/00501, PCT/AU00/00502, PCT/AU00/00503, PCT/AU00/00504, PCI /AU00/00505, PCT/AU00/00506, PCT/AUOO/00507, PCT/AU00/00508, PCT/AU00/00509, PCT/AU00/00510, PCT/AU00/00512, PCT/AUOO/00513, PCT/AUOO/00514, PCT/AU00/00515 The disclosures of these co-pending applications are incorporated herein by cross-reference RECTIFIED SHEET A distribution system of the above kind will output page data in a particular format, providing image data in a range of image planes These image planes may be received at pπnters with pπnt heads not fitted with a corresponding number of ink channels Some clients to the system might desire to move image planes from one ink channel to another A pπnt engine/controller ideally addresses these issues More speed and flexibility in selection of output channels at the print head depends on development of both pπnt head and its engine/controller The pπnt engine/controller architecture ideally needs to be designed to push data in volume to selected ink channels in the pπnt head at high speed SUMMARY OF THE INVENTION In one form the invention resides in a pπnt engine/controller to dπve an ink drop pπnt head comprising an interface at which to receive compressed page data, decoders to decode respective types of image planes in the received compressed page data, and a half-toner/compositor to composite image plane data, the half-toner/compositor including a dot merger unit taking bits from the respective planes as inputs, and a color mask register holding masking bits m number equal to the number of image planes, respective input bits to the dot merger unit being ANDed with respective color mask register bits and the resultant bits Ored together to form an output bit in a channel for which there is an ink at the pnnt head The dot merger unit provides a means by which to map data bits to the respective inks at a pπnt head A color mask register within the dot merger unit holds a pattern of bits that effect the mapping of image bits input to the dot merger unit Image data might be delivered to a client with image planes in all of CMY and K together with data to go into tags on an output page in infrared ink Speed might be such that a fixative needs to be used The ideal pπnt head then works with six ink channels Some printers may not provide for all of CMY and K and K may need to be expressed through use of the CMY channels It might be desired in some circumstances to put a high-resolution plane otherwise destined for the K channel into one of the color channels These outcomes are met through what bits are loaded into the color mask register BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 is a diagram illustrating data flow and the functions performed by the pπnt engine controller FIG 2 shows the pπnt engine controller in the context of the overall pπnter system architecture FIG 3 illustrates the pnnt engine controller architecture FIG 4 illustrates the external interfaces to the halftoner/compositor unit (HCU) of FIG 3 FIG 5 is a diagram showing internal circuitry to the HCU of FIG 4 FIG 6 shows a block diagram illustrating the process within the dot merger unit of FIG 5 FIG 7 shows a diagram illustrating the process within the dot reorganization unit of FIG 5 FIG 8 shows a diagram illustrating the process within the line loader/format unit (LLFU) of FIG 5 FIG 9 is a diagram showing internal circuitry to generate color data in the LLFU of FIG 8 FIGs 10 and 11 illustrate components of the LLFU seen in FIG 9 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A typically 12 inch pπnt head width is controlled by one or more PECs, as descπbed below, to allow full-bleed pπnting of both A4 and Letter pages Six channels of colored ink are the expected maximum in the present pπnting environment, these being • CMY, for regular color pπnting • K, for black text and other black pπnting • IR (infrared), for tag-enabled applications • F (fixative), to enable pπnting at high speed Because the pπnter is to be capable of fast printing, a fixative may be required to enable the ink to dry before the next page has completed pπnting at higher speeds Otherwise the pages might bleed on each other In lower speed pπnting environments the fixative will not be required A PEC might be built in a single chip to interface with a pnnt head It will contain four basic levels of functionality • receiving compressed pages via a seπal interface such as IEEE 1394 • a pπnt engine for producing a page from a compressed form The pπnt engine functionality includes expanding the page image, ditheπng the contone layer, compositing the black layer over the contone layer, optionally adding infrared tags, and sending the resultant image to the print head • a pπnt controller for controlling the print head and stepper motors • two standard low-speed seπal ports for communication with QA chips Note that there ought to be two ports and not a single port to ensure strong secuπty dunng the authentication procedure In Figure 1 is seen the flow of data to send a document from computer system to pπnted page A document is received at 1 1 and loaded to memory buffer 12 wherein page layouts may be effected and any required objects might be added Pages from memory 12 are rasteπzed at 13 and compressed at 14 pπor to transmission to the pπnt engine controller 10 Pages are received as compressed page images within the pπnt engine controller 10 into a memory buffer 15, from which they are fed to a page expander 16 wherein page images are retπeved Any requisite dither might be applied to any contone layer at 17 Any black bi-level layer might be composited over the contone layer at 18 together with any infrared tags at 19 The composited page data is pπnted at 20 to produce page 21 The pπnt engine/controller takes the compressed page image and starts the page expansion and pπnting in pipeline fashion Page expansion and printing is preferably pipelined because it is impractical to store a sizable bi-level CMYK+IR page image in memory The first stage of the pipeline expands a JPEG-compressed contone CMYK layer (see below), expands a Group 4 Fax-compressed bi-level dither matπx selection map (see below), and expands a Group 4 Fax-compressed high resolution black layer (see below), all in parallel In parallel with this, the tag encoder encodes bi-level IR tags with data from the compressed page image The second stage dithers the contone CMYK layer using a dither matπx selected by the dither matπx select map, composites the bi-level black layer over the resulting bi-level K layer and adds the IR layer to the page A fixative layer is also generated at each dot position wherever there is a need in any of C, M, Y, K, or IR channels The last stage pπnts the bi-level CMYK+IR data through the pπnt head via a pπnt head interface (see below) In FIG 2 is seen how the pnnt engine/controller 10 fits within the overall pπnter system architecture The various components of the printer system might include • a Print Engine/Controller (PEC) A PEC chip 10, or chips, is responsible for receiving the compressed page images for storage in a memory buffer 24, performing the page expansion, black layer compositing and sending the dot data to the pπnt head 23 It may also communicate with QA chips 25,26 and provides a means of retnev g pπnt head characteπstics to ensure optimum pnnting The PEC is the subject of this specification • a memory buffer The memory buffer 24 is for storing the compressed page image and for scratch use dunng the printing of a given page The construction and working of memory buffers is known to those skilled in the art and a range of standard chips and techniques for their use might be utilized in use of the PEC of the invention • a master QA chip The master chip 25 is ideally matched to replaceable ink cartridge QA chips 26 The construction and working of QA units is known to those skilled in the art and a range of known QA processes might be utilized in use of the PEC of the invention For example, a QA chip is descπbed in co-pending United States Patent Applications QA chip communication may be best included within the overall functionality of the PEC chip since it has a role in the expansion of the image as well as running the physical pnnt head By locating QA chip communication there it can be ensured that there is enough ink to pπnt the page Preferably the QA embedded in the pnnt head assembly is implemented using an authentication chip Since it is a master QA chip, it only contains authentication keys, and does not contain user-data However, it must match the ink cartridge's QA chip The QA chip in the ink cartπdge contains information required for maintaining the best possible pnnt quality, and is implemented using an authentication chip Preferably a 64 MBit (8 MByte) memory buffer is used to store the compressed page image While one page is being wπtten to the buffer another is being read (double buffeπng) In addition, the PEC uses the memory to buffer the calculated dot information during the pπnting of a page Dunng the pπnting of page N, the buffer is used for • Reading compressed page N • Reading and writing the bi-level dot information for page N • Wnting compressed page N+l Preferably a PEC chip will incorporate a simple micro-controller CPU core 35 to perform the following functions • perform QA chip authentication protocols via seπal interface 36 between pπnt pages • run the stepper motor via a parallel interface 91 dunng a print (the stepper motor requires a 5 KHz process) • synchronize the vaπous portions of the PEC chip dunng a pπnt • provide a means of interfacing with external data requests (programming registers etc ) • provide a means of interfacing with print head segment low-speed data requests (such as reading the charactenzation vectors and wnting pulse profiles) • provide a means of wnting the portrait and landscape tag structures to external DRAM Since all of the image processing is performed by dedicated hardware, the CPU does not have to process pixels As a result, the CPU can be extremely simple A wide variety of known CPU cores are suitable it can be any processor core with sufficient processing power to perform the required calculations and control functions fast enough An example of a suitable core is a Philips 8051 micro-controller running at about 1 MHz Associated with the CPU core 35 may be a program ROM and a small program scratch RAM The CPU communicates with the other units within the PEC chip via memory-mapped I/O Particular address ranges may map to particular units, and within each range, to particular registers within that particular unit This includes the seπal 36 and parallel 91 interfaces A small program flash ROM may be incorporated into the PEC chip Its size depends on the CPU chosen, but should not be more than 8KB Likewise, a small scratch RAM area can be incorporated into the PEC chip Since the program code does not have to manipulate images, there is no need for a large scratch area The RAM size depends on the CPU chosen (e g stack mechanisms, subroutine calling conventions, register sizes etc ), but should not be more than about 2 KB A PEC chip using the above referenced segment based page wide print head can reproduce black at a full dot resolution (typically 1600 dpi), but reproduces contone color at a somewhat lower resolution using halftoning The page descπption is therefore divided into a black bi-level layer and a contone layer The black bi-level layer is defined to composite over the contone layer The black bi-level layer consists of a bitmap containing a 1-bit opacity for each pixel This black layer matte has a resolution that is an integer factor of the pnnter's dot resolution The highest supported resolution is 1600 dpi, I e the pnnter's full dot resolution The contone layer consists of a bitmap containing a 32-bit CMYK color for each pixel, where K is optional This contone image has a resolution that is an integer factor of the pnnter's dot resolution The highest supported resolution is 320 ppi over 12 inches for a single PEC, l e one-fifth the pnnter's dot resolution For higher contone resolutions multiple PECs are required, with each PEC producing an stnp of the output page The contone resolution is also typically an integer factor of the black bi-level resolution, to simplify calculations in the RIPs This is not a requirement, however The black bi-level layer and the contone layer are both in compressed form for efficient storage in the pnnter's internal memory In FIG 3 is seen the pπnt engine architecture The pnnt engine's page expansion and pπnting pipeline consists of a high speed seπal interface 27 (such as a standard IEEE 1394 interface), a standard JPEG decoder 28, a standard Group 4 Fax decoder , a custom halftoner/compositor unit 29, a custom tag encoder 30, a line loader/formatter unit 31, and a custom interface 32 to the pπnt head 33 The decoders 28,88 and encoder 30 are buffered to the halftoner/compositor 29 The tag encoder 30 establishes an infrared tag or tags to a page according to protocols dependent on what uses might be made of the page and the actual content of a tag is not the subject of the present invention The pπnt engine works in a double buffered way One page is loaded into DRAM 34 via DRAM interface 89 and data bus 90 from the high speed senal interface 27 while the previously loaded page is read from DRAM 34 and passed through the pπnt engine pipeline Once the page has finished pπnting, then the page just loaded becomes the page being pπnted, and a new page is loaded via the high-speed senal interface 27 At the first stage the pipeline expands any JPEG-compressed contone (CMYK) layer, and expands any of two Group 4 Fax-compressed bi-level data streams The two streams are the black layer (although the PEC is actually color agnostic and this bi-level layer can be directed to any of the output inks), and a matte for selecting between dither matnces for contone ditheπng (see below) At the second stage, in parallel with the first, is encoded any tags for later rendeπng in either IR or black ink Finally the third stage dithers the contone layer, and composites position tags and the bi-level spotl layer over the resulting bi-level dithered layer The data stream is ideally adjusted to create smooth transitions across overlapping segments in the pπnt head and ideally it is adjusted to compensate for dead nozzles in the pnnt head Up to 6 channels of bi-level data are produced from this stage Note that not all 6 channels may be present on the pπnt head For example, the pπnt head may be CMY only, with K pushed into the CMY channels and IR ignored Alternatively, the position tags may be printed in K if IR ink is not available (or for testing purposes) The resultant bi-level CMYK-IR dot-data is buffered and formatted for pnnting on the pnnt head 33 via a set of line buffers (see below) The majonty of these line buffers might be ideally stored on the off- chip DRAM 34 The final stage pπnts the 6 channels of bi-level dot data via the pπnt head interface 32 Compression is used in a pπnting system that employs the PEC This is to reduce bandwidth requirements between a host and PEC, as well as to reduce memory requirements for page storage At 267 ppi, a Letter page of contone CMYK data has a size of 25MB Using lossy contone compression algorithms such as JPEG (see below), contone images compress with a ratio up to 10 1 without noticeable loss of quality, giving a compressed page size of 2 5MB At 800 dpi, a Letter page of bi-level data has a size of 7MB Coherent data such as text compresses very well Using lossless bi-level compression algonthms such as Group 4 Facsimile (see below), ten-point text compresses with a ratio of about 10 1, giving a compressed page size of 0 8MB Once dithered, a page of CMYK contone image data consists of 114MB of bi-level data The two-layer compressed page image format descπbed below exploits the relative strengths of lossy JPEG contone image compression and lossless bi-level text compression The format is compact enough to be storage-efficient, and simple enough to allow straightforward real-time expansion dunng pπnting Since text and images normally don't overlap, the normal worst-case page image size is 2 5MB (I e image only), while the normal best-case page image size is 0 8MB (l e text only) The absolute worst-case page image size is 3 3MB (l e text over image) Assuming a quarter of an average page contains images, the average page image size is 1 2MB A Group 3 Facsimile compression algoπthm (see ANSI/EIA 538-1988, Facsimile Coding Schemes and Coding Control Functions for Group 4 Facsimile Equipment, August 1988) can be used to losslessly compresses bi- level data for transmission over slow and noisy telephone lines The bi-level data represents scanned black text and graphics on a white background, and the algonthm is tuned for this class of images (it is explicitly not tuned, for example, for halftoned bi-level images) The ID Group 3 algoπthm runlength-encodes each scanhne and then Huffman-encodes the resulting mnlengths Runlengths in the range 0 to 63 are coded with terminating codes Runlengths in the range 64 to 2623 are coded with make-up codes, each representing a multiple of 64, followed by a terminating code Runlengths exceeding 2623 are coded with multiple make-up codes followed by a terminating code The Huffman tables are fixed, but are separately tuned for black and white runs (except for make-up codes above 1728, which are common) When possible, the 2D Group 3 algoπthm encodes a scanhne as a set of short edge deltas (0, ±1, ±2, ±3) with reference to the previous scanhne The delta symbols are entropy-encoded (so that the zero delta symbol is only one bit long etc ) Edges within a 2D-encoded line that can't be delta-encoded are runlength-encoded, and are identified by a prefix 1 D- and 2D-encoded lines are marked differently ID-encoded lines are generated at regular intervals, whether actually required or not, to ensure that the decoder can recover from line noise with minimal image degradation 2D Group 3 achieves compression ratios of up to 6 1 (see Urban, S J , "Review of standards for electronic imaging for facsimile systems", Journal of Electronic Imaging, Vol 1(1), January 1992, pp 5-21) A Group 4 Facsimile algonthm (see ANSI EIA 538-1988, Facsimile Coding Schemes and Coding Control Functions for Group 4 Facsimile Equipment, August 1988) losslessly compresses bi-level data for transmission over error-free communications lines (I e the lines are truly error-free, or error-correction is done at a lower protocol level) The Group 4 algonthm is based on the 2D Group 3 algoπthm, with the essential modification that since transmission is assumed to be error- free, ID-encoded lines are no longer generated at regular intervals as an aid to eπor-recovery Group 4 achieves compression ratios ranging from 20 1 to 60 1 for the CCITT set of test images The design goals and performance of the Group 4 compression algoπthm qualify it as a compression algonthm for the bi-level layers However, its Huffman tables are tuned to a lower scanning resolution (100-400 dpi), and it encodes runlengths exceeding 2623 awkwardly At 800 dpi, our maximum runlength is cuπently 6400 Although a Group 4 decoder core would be available for use in PEC, it might not handle runlengths exceeding those normally encountered in 400 dpi facsimile applications, and so would require modification The (typically 1600 dpi) black layer is losslessly compressed using G4Fax at a typical compression ratio exceeding 10 1 A (typically 320dpi) dither matrix select layer, which matches the contone color layer, is losslessly compressed using G4Fax at a typical compression ratio exceeding 50 1 The Group 4 Fax (G4 Fax) decoder is responsible for decompressing bi-level data Bi-level data is limited to a single spot color (typically black for text and line graphics), and a dither matπx select bit-map for use in subsequent dithenng of the contone data (decompressed by the JPEG decoder) The input to the G4 Fax decoder is 2 planes of bi- level data, read from the external DRAM The output of the G4 Fax decoder is 2 planes of decompressed bi-level data The decompressed bi-level data is sent to the Halftoner/Compositor Unit (HCU) for the next stage in the pnntmg pipeline Two bi-level buffers provides the means for transferring the bi-level data between the G4 Fax decoder and the HCU Each decompressed bi-level layer is output to two line buffers Each buffer is capable of holding a full 12 inch line of dots at the expected maximum resolution Having two line buffers allows one line to be read by the HCU while the other line is being wπtten to by the G4 Fax decoder This is important because a single bi-level line is typically less than 1600 dpi, and must therefore be expanded in both the dot and line dimensions If the buffenng were less than a full line, the G4 Fax decoder would have to decode the same line multiple times - once for each output 600dpi dothne Spot color 1 is designed to allow high resolution dot data for a single color plane of the output image While the contone layers provide adequate resolution for images, spot color 1 is targeted at applications such as text and line graphics (typically black) When used as text and line graphics, the typical compression ratio exceeds 10 1 Spot color 1 allows vanable resolution up to 1600dpi for maximum pπnt quality Each of the two line buffers is therefore total 2400 bytes (12 inches x 1600 dpi = 19,200 bits) The resolution of the dither matnx select map should ideally match the contone resolution Consequently each of the two line buffers is therefore 480 bytes (3840 bits), capable of stonng 12 inches at 320 dpi When the map matches the contone resolution, the typical compression ratio exceeds 50 1 In order to provide support for • 800 dpi spot color 1 layer (typically black) • 320 dpi dither matπx select layer the decompression bandwidth requirements are 9 05 MB/sec for 1 page per second performance (regardless of whether the page width is 12 inches or 8 5 inches), and 20 MB/sec and 14 2 MB/sec for 12 inch and 8 5 inch page widths respectively dunng maximum pnnter speed performance (30,000 lines per second) Given that the decompressed data is output to a line buffer, the G4 Fax decoder can readily decompress a line from each of the outputs one at a time The G4 Fax decoder is fed directly from the main memory via the DRAM interface The amount of compression determines the bandwidth requirements to the external DRAM Since G4 Fax is lossless, the complexity of the image impacts on the amount of data and hence the bandwidth typically an 800 dpi black text/graphics layer exceeds 10 1 compression, so the bandwidth required to pnnt 1 page per second is 078 MB/sec Similarly, a typical 320 dpi dither select matπx compresses at more than 50 1, resulting m a 0025 MB/sec bandwidth The fastest pnnting speed configuration of 320 dpi for dither select matπx and 800 dpi for spot color 1 requires bandwidth of 1 72 MB/sec and 0 056 MB/sec respectively A total bandwidth of 2 MB/sec should therefore be more than enough for the DRAM bandwidth The G4 Fax decoding functionality is implemented by means of a G4 Fax Decoder core A wide variety of G4Fax Decoder cores are suitable it can be any core with sufficient processing power to perform the required calculations and control functions fast enough It must be capable of handling runlengths exceeding those normally encountered in 400 dpi facsimile applications, and so may require modification A JPEG compression algorithm (see ISO/IEC 19018-1 1994, Information technology - Digital compression and coding of continuous-tone still images Requirements and guidelines, 1994) lossily compresses a contone image at a specified quality level It introduces imperceptible image degradation at compression ratios below 5 1, and negligible image degradation at compression ratios below 10 1 (see Wallace, G K , "The JPEG Still Picture Compression Standard", Communications of the ACM, Vol 34, No 4, Apnl 1991, pp 30-44) JPEG typically first transforms the image into a color space that separates luminance and chrominance into separate color channels This allows the chrominance channels to be subsampled without appreciable loss because of the human visual system's relatively greater sensitivity to luminance than chrominance After this first step, each color channel is compressed separately The image is divided into 8x8 pixel blocks Each block is then transformed into the frequency domain via a discrete cosine transform (DCT) This transformation has the effect of concentrating image energy in relatively lower- frequency coefficients, which allows higher-frequency coefficients to be more crudely quantized This quantization is the pπncipal source of compression in JPEG Further compression is achieved by ordeπng coefficients by frequency to maximize the likelihood of adjacent zero coefficients, and then runlength-encoding runs of zeroes Finally, the runlengths and non-zero frequency coefficients are entropy coded Decompression is the inverse process of compression The CMYK (or CMY) contone layer is compressed to a planar color JPEG bytestream If luminance/chrominance separation is deemed necessary, either for the purposes of table shaπng or for chrominance subsamphng, then CMYK is converted to YCrCb and Cr and Cb are duly subsampled The JPEG bytestream is complete and self-contained It contains all data required for decompression, including quantization and Huffman tables The JPEG decoder is responsible for performing the on-the-fly decompression of the contone data layer The input to the JPEG decoder is up to 4 planes of contone data This will typically be 3 planes, representing a CMY contone image, or 4 planes representing a CMYK contone image Each color plane can be in a different resolution, although typically all color planes will be the same resolution The contone layers are read from the external DRAM The output of the JPEG decoder is the decompressed contone data, separated into planes The decompressed contone image is sent to the halftoner/compositor unit (HCU) 29 for the next stage in the pπnting pipeline The 4-plane contone buffer provides the means for transfernng the contone data between the JPEG decoder and the HCU 29 Each color plane of the decompressed contone data is output to a set of two line buffers (see below) Each line buffer is 3840 bytes, and is therefore capable of holding 12 inches of a single color plane's pixels at 320 ppi The line buffeπng allows one line buffer to be read by the HCU while the other line buffer is being wntten to by the JPEG decoder This is important because a single contone line is typically less than 1600 ppi, and must therefore be expanded in both the dot and line dimensions If the buffeπng were less than a full line, the JPEG decoder would have to decode the same line multiple times - once for each output 600dpi dothne Although a vaπety of resolutions is supported, there is a tradeoff between the resolution and available bandwidth As resolution and number of colors increase, bandwidth requirements also increase In addition, the number of segments being targeted by the PEC chip also affects the bandwidth and possible resolutions Note that since the contone image is processed m a planar format, each color plane can be stored at a different resolution (for example CMY may be a higher resolution than the K plane) The highest supported contone resolution is lόOOppi (matching the pnnter's full dot resolution) However there is only enough output line buffer memory to hold enough contone pixels for a 320ppι line of length 12 inches If the full 12 inches of output was required at higher contone resolution, multiple PEC chips would be required, although it should be noted that the final output on the pπnter will still only be bi-level With support for 4 colors at 320ppι, the decompression output bandwidth requirements are 40 B/sec for 1 page per second performance (regardless of whether the page width is 12 inches or 8 5 inches), and 88 MB/sec and 64 MB/sec for 12 inch and 8 5 inch page widths respectively dunng maximum printer speed performance (30,000 lines per second) The JPEG decoder is fed directly from the main memory via the DRAM interface The amount of compression determines the bandwidth requirements to the external DRAM As the level of compression increases, the bandwidth decreases, but the quality of the final output image can also decrease The DRAM bandwidth for a single color plane can be readily calculated by applying the compression factor to the output bandwidth For example, a single color plane at 320 ppi with a compression factor of 10 1 requires 1 MB/sec access to DRAM to produce a single page per second The JPEG functionality is implemented by means of a JPEG core A wide vaπety of JPEG cores are suitable it can be any JPEG core with sufficient processing power to perform the required calculations and control functions fast enough For example, the BTG X-Match core has decompression speeds up to 140 MBytes/sec, which allows decompression of 4 color planes at contone resolutions up to 400ppι for the maximum pπnter speed (30,000 lines at 1600dpi per second), and 800ppι for 1 page/sec pπnter speed Note that the core needs to only support decompression, reducing the requirements that are imposed by more generalized JPEG compression/decompression cores The size of the core is expected to be no more than 100,000 gates Given that the decompressed data is output to a line buffer, the JPEG decoder can readily decompress an entire line for each of the color planes one at a time, thus saving on context switching dunng a line and simplifying the control of the JPEG decoder 4 contexts must be kept (1 context for each color plane), and includes current address m the external DRAM as well as appropnate JPEG decoding parameters In FIG 4 the halftoner/compositor unit (HCU) 29 combines the functions of halftoning the contone (typically CMYK) layer to a bi-level version of the same, and compositing the spotl bi-level layer over the appropnate halftoned contone layer(s) If there is no K ink in the pnnter, the HCU 29 is able to map K to CMY dots as appropriate It also selects between two dither matnces on a pixel by pixel basis, based on the corresponding value in the dither matnx select map The input to the HCU 29 is an expanded contone layer (from the JPEG decoder unit) through buffer 37, an expanded bi-level spotl layer through buffer 38, an expanded dither-matπx-select bitmap at typically the same resolution as the contone layer through buffer 39, and tag data at full dot resolution through buffer 40 The HCU 29 uses up to two dither matnces, read from the external DRAM 34 The output from the HCU 29 to the line loader/format unit (LLFU) at 41 is a set of pπnter resolution bi-level image lines in up to 6 color planes Typically, the contone layer is CMYK or CMY, and the bi-level spotl layer is K In FIG 5 is seen the HCU in greater detail Once started, the HCU proceeds until it detects an end-of-page condition, or until it is explicitly stopped via its control register The first task of the HCU is to scale, in the respective scale units such as the scale unit 43, all data, received in the buffer planes such as 42, to pπnter resolution both honzontally and vertically The scale unit provides a means of scaling contone or bi-level data to pπnter resolution both honzontally and vertically Scaling is achieved by replicating a data value an integer number of times in both dimensions Processes by which to scale data will be familiar to those skilled in the art Two control bits are provided to the scale unit 43 by the margin unit 57 advance dot and advance line The advance dot bit allows the state machine to generate multiple instances of the same dot data (useful for page margins and creating dot data for overlapping segments in the pπnt head) The advance line bit allows the state machine to control when a particular line of dots has been finished, thereby allowing truncation of data according to pπnter margins It also saves the scale unit from requiπng special end-of-hne logic The input to the scale unit is a full line buffer The line is used scale factor times to effect vertical up-scaling via line replication, and within each line, each value is used scale factor times to effect horizontal up-scaling via pixel replication Once the input line has been used scale factor times (the advance line bit has been set scale factor times), the input buffer select bit of the address is toggled (double buffering) The logic for the scale unit is the same for the 8-bit and 1-bit case, since the scale unit only generates addresses Since each of the contone layers can be a different resolution, they are scaled independently The bi-level spotl layer at buffer 45 and the dither matπx select layer at buffer 46 also need to be scaled The bi-level tag data at buffer 47 is established at the correct resolution and does not need to be scaled The scaled-up dither matπx select bit is used by the dither matπx access unit 48 to select a single 8-bit value from the two dither matrices The 8-bit value is output to the 4 comparators 44, and 49 to 51 , which simply compare it to the specific 8-bit contone value The generation of an actual dither matπx is dependent on the structure of the pnnt head and the general processes by which to generate one will be familiar to those skilled in the art If the contone value is greater than or equal to the 8-bit dither matnx value a 1 is output If not, then a 0 is output These bits are then all ANDed at 52 to 56 with an inPage bit from the margin unit 57 (whether or not the particular dot is inside the pπntable area of the page) The final stage in the HCU is the compositing stage For each of the 6 output layers there is a single dot merger unit, such as unit 58, each with 6 inputs The single output bit from each dot merger unit is a combination of any or all of the input bits This allows the spot color to be placed in any output color plane (including infrared for testing purposes), black to be merged into cyan, magenta and yellow (if no black mk is present in the pnnt head), and tag dot data to be placed in a visible plane A fixative color plane can also be readily generated The dot reorg unit (DRU) 59 is responsible for taking the generated dot stream for a given color plane and organizing it into 32-bit quantities so that the output is in segment order, and in dot order within segments Minimal reordeπng is required due to the fact that dots for overlapping segments are not generated in segment order Two control bits are provided to the scale units by the margin unit 57 advance dot and advance line The advance dot bit allows the state machine to generate multiple instances of the same dot data (useful for page margins and creating dot data for overlapping segments in the pπnt head) The advance line bit allows the state machine to control when a particular line of dots has been finished, thereby allowing truncation of data according to pπnter margins It also saves the scale unit from requiπng special end-of-hne logic The comparator unit contains a simple 8-bit "greater-than-or-equal" comparator It is used to determine whether the 8-bit contone value is greater than or equal to the 8-bit dither matnx value As such, the comparator unit takes two 8- bit inputs and produces a single 1-bit output In FIG 6 is seen more detail of the dot merger unit It provides a means of mapping the bi-level dithered data, the spotl color, and the tag data to output inks in the actual pπnt head Each dot merger unit takes 6 1-bit inputs and produces a single bit output that represents the output dot for that color plane The output bit at 60 is a combination of any or all of the input bits This allows the spot color to be placed in any output color plane (including infrared for testing purposes), black to be merged into cyan, magenta and yellow (in the case of no black ink in the pπnt head), and tag dot data to be placed in a visible plane An output for fixative can readily be generated by simply combining all of the input bits The dot merger unit contains a 6-bit ColorMask register 61 that is used as a mask against the 6 input bits Each of the input bits is ANDed with the coπespondmg ColorMask register bit, and the resultant 6 bits are then ORed together to form the final output bit The ColorMask registers for each output are set depending on the meaning of the input layers and the available Assuming contone layer 1 is cyan, contone layer 2 is magenta, contone layer 3 is yellow, and contone layer 4 is black, bi-level spotl is black, bi-level tag is infra-red * If the pπnt head does not contain black ink, the ColorMask registers for Cyan, Magenta and Yellow would be 01 1001 , 01 1010, and 01 1100 respectively, thus placing the black ink into each of cyan, magenta, and yellow * If all inks require fixative, the ColorMask for fixative would be 11 1 1 1 1 If infrared does not require fixative, the ColorMask register for fixative would be 01 1 1 1 1 * If black ink is present in the pnnt head, and for testing purposes we want to view the tags, simply set bιt5 of the black color channel's ColorMask register Bιt5 of the infrared channel's ColorMask register can be set or cleared as desired dunng this testing mode The Spotl color can be set to any base color simply by setting the appropnate bit of the ColorMask register For example * If spotl color is cyan, the cyan ColorMask register would be 010001 * If spotl color is yellow, the yellow ColorMask register would be 010100 * If spotl color is green, the cyan and yellow ColorMask registers would be 010001 and 010100 respectively, to enable spotl onto both cyan and yellow inks * If spotl color is some special ink, such as gold, it can be enabled into an ink channel simply by setting the ColorMask register of that channel to 010000 Tags, spot 1 and potentially contone planes should be appropπately directed For example, there are only 5 dot merger units but 6 inputs consequently one input is either ignored or merged For example, if spotl is gold and contone contains a black layer, then black contone should be pushed into C, M and Y by setting the ColorMask registers for Cyan, Magenta and Yellow to 011001 , 011010, and 011100 respectively A fixative plane can readily be generated by selecting the bits that represent inks requiπng the presence of fixative For example * If all inks require fixative, the ColorMask register for fixative would be 11 11 11 * If only black requires fixative, and spotl and contone 4 represent black, the ColorMask register for fixative would be 011000 * If none of the cyan, magenta, yellow or black inks require fixative, but the infra-red ink requires fixative, the ColorMask register for fixative would be 100000 In FIG 7 is seen the dot reorg unit (DRU) which is responsible for taking the generated dot stream for a given color plane and organizing it into 32-bit quantities so that the output is in segment order, and in dot order within segments Minimal reordeπng is required due to the fact that dots for overlapping segments are not generated in segment order The DRU contains a 32-bit shift register, a regular 32-bit register, and a regular 16-bit register A 5-bit counter keeps track of the number of bits processed so far The dot advance signal from the dither matπx access unit (DMAU) is used to instruct the DRU as to which bits should be output In FIG 7 regιster(A) 62 is clocked every cycle It contains the 32 most recent dots produced by the dot merger unit (DMU) The full 32-bit value is copied to regιster(B) 63 every 32 cycles by means of a WπteEnable signal produced by the DRU state machine 64 via a simple 5-bit counter The 16 odd bits (bits 1, 3, 5, 7 etc ) from regιster(B) 63 are copied to regιster(C) 65 with the same WπteEnable pulse A 32-bit multiplexor 66 then selects between the following 3 outputs based upon 2 bits from the state machine • the full 32 bits from register B • A 32-bit value made up from the 16 even bits of register A (bits 0, 2, 4, 6 etc ) and the 16 even bits of register B The 16 even bits from register A form bits 0 to 15, while the 16 even bits from register B form bits 16-31 • A 32-bit value made up from the 16 odd bits of register B (bits 1, 3, 5, 7 etc ) and the 16 bits of register C The bits of register C form bits 0 to 15, while the odd bits from register B form bits 16-31 The state machine for the DRU can be seen in Table 1 It starts in state 0 It changes state every 32 cycles During the 32 cycles a single noOverlap bit collects the AND of all the dot advance bits for those 32 cycles {noOverlap ■ ■ dot advance for cycle 0, and noOverlap = noOverlap AND dot advance for cycles 1 to 31) Table 1. State machine for DRU The margin unit (MU) 57, in FIG 5, is responsible for turning advance dot and advance line signals from the dither matπx access unit (DMAU) 48 into general control signals based on the page margins of the current page It is also responsible for generating the end of page condition The MU keeps a counter of dot and line across the page Both are set to 0 at the beginning of the page The dot counter is advanced by 1 each time the MU receives a dot advance signal from the DMAU When the MU receives a line advance signal from the DMAU, the line counter is incremented and the dot counter is reset to 0 Each cycle, the current line and dot values are compared to the margins of the page, and appropnate output dot advance, line advance and within margin signals are given based on these margins The DMAU contains the only substantial memory requirements for the HCU In FIG 8 is seen the line loader / format unit (LLFU) It receives dot information from the HCU, loads the dots for a given pnnt line into appropnate buffer storage (some on chip, and some in external DRAM 34) and formats them into the order required for the pπnt head A high level block diagram of the LLFU in terms of its external interface is shown in FIG 9 The input 67 to the LLFU is a set of 6 32-bit words and a DataValid bit, all generated by the HCU The output 68 is a set of 90 bits representing a maximum of 15 pnnt head segments of 6 colors Not all the output bits may be valid, depending on how many colors are actually used in the pπnt head The physical placement of finng nozzles on the pnnt head referenced above, nozzles in two offset rows, means that odd and even dots of the same color are for two different lines The even dots are for line L, and the odd dots are for line L-2 In addition, there is a number of lines between the dots of one color and the dots of another Since the 6 color planes for the same dot position are calculated at one time by the HCU, there is a need to delay the dot data for each of the color planes until the same dot is positioned under the appropnate color nozzle The size of each buffer line depends on the width of the pπnt head Since a single PEC generates dots for up to 15 pπnt head segments, a single odd or even buffer line is therefore 15 sets of 640 dots, for a total of 9600 bits (1200 bytes) For example, the buffers required for color 6 odd dots totals almost 45 KBytes The entire set of requisite buffers might be provided on the PEC chip when manufactunng techniques are capable Otherwise, the buffers for colors 2 onward may be stored in external DRAM This enables the PEC to be valid even though the distance between color planes may change in the future It is trivial to keep the even dots for color 1 on PEC, since everything is pπnted relative to that particular dot line (no additional line buffers are needed) In addition, the 2 half-lines required for buffeπng color 1 odd dots saves substantial DRAM bandwidth The various line buffers (on chip and in DRAM) need to be pre-loaded with all 0s before the page is pπnted so that it has clean edges The end of the page is generated automatically by the HCU so it will have a clean edge In FIG 10 is seen a block diagram for Color N OESpht (see Oespht 70 of FIG 9), and the block diagram for each of the two buffers E and F, 71,72 in FIG 9 can be found in FIGs 10 and 11 Buffer EF is a double buffered mechanism for transferπng data to the pnnt head interface (PHI) 32 in FIG 3 Buffers E and F therefore have identical structures Dunng the processing of a line of dots, one of the two buffers is wπtten to while the other is being read from The two buffers are logically swapped upon receipt of the line-sync signal from the PHI Both buffers E and F are composed of 6 sub-buffers, 1 sub-buffer per color, as shown in FIG 1 1 , the color 1 sub-buffer numbered 73 The size of each sub-buffer is 2400 bytes, enough to hold 15 segments at 1280 dots per segment The memory is accessed 32-bits at a time, so there are 600 addresses for each sub-buffer (requinng 10 bits of address) All the even dots are placed before the odd dots in each color's sub-buffer If there is any unused space (for pnnting to fewer than 15 segments) it is located at the end of each color's sub-buffer The amount of memory actually used from each sub-buffer is directly related to the number of segments actually addressed by the PEC For a 15 segment print head there are 1200 bytes of even dots followed by 1200 bytes of odd dots, with no unused space The number of sub-buffers gainfully used is directly related to the number of colors used in the pnnt head The maximum number of colors supported is 6 The addressing decoding circuitry for each of buffers E and F is such that in a given cycle, a single 32-bit access can be made to all 6 sub-buffers - either a read from all 6 or a wnte to one of the 6 Only one bit of the 32-bits read from each color buffer is selected, for a total of 6 output bits The process is shown in FIG 11 15 bits of address allow the reading of a particular bit by means of 10-bιts of address being used to select 32 bits, and 5-bιts of address choose 1-bit from those 32 Since all color sub-buffers share this logic, a single 15-bit address gives a total of 6 bits out, one bit per color Each sub-buffer 73 to 78 has its own WnteEnable line, to allow a single 32-bit value to be wπtten to a particular color buffer in a given cycle The individual WπteEnables are generated by ANDing the single WnteEnable input with the decoded form of ColorSelect The 32-bits of Dataln on line 79 are shared, since only one buffer will actually clock the data in Address generation for reading from buffers E and F is straightforward Each cycle generates a bit address that is used to fetch 6 bits representing 1-bit per color for a particular segment By adding 640 to the current bit address, we advance to the next segment's equivalent dot We add 640 (not 1280) since the odd and even dots are separated in the buffer We do this NumSegments times to retπeve the data representing the even dots, and transfer those bits to the PHI When NumSegments = 15, the number of bits is 90 (15 x 6 bits) The process is then repeated for the odd dots This entire even odd bit generation process is repeated 640 times, incrementing the start address each time Thus all dot values are transferred to the PHI in the order required by the pnnt head in 640 x 2 x NumSegments cycles When NumSegments = 15, the number of cycles is 19,200 cycles Note that regardless of the number of colors actually used in the print head, 6 bits are produced in a given read cycle (one bit from each color's buffer) In addition, we generate the TWriteEnable control signal for wnting to the 90-bit Transfer register 90 in FIG 9 Since the LLFU starts before the PHI, we must transfer the first value before the Advance pulse from the PHI We must also generate the next value in readiness for the first Advance pulse The solution is to transfer the first value to the Transfer register after NumSegments cycles, and then to stall NumSegments cycles later, waiting for the Advance pulse to start the next NumSegments cycle group Once the first Advance pulse arnves, the LLFU is synchronized to the PHI The read process for a single dothne is shown in the following pseudocode DoneFirst = FALSE WantToXfer = FALSE For DotlnSegmentO = 0 to 1279 If (DotlnSegmentO bitO == 0) CurrAdr = DotlnSegmentO (high bits) (puts in range 0 to 639) Endlf XfersRemaining = NumSegments Do WantToXfer = (XfersRemaining == 0) TWπteEnable = (WantToXfer AND NOT DoneFirst) OR PHI ADVANCE DoneFirst = DoneFirst OR TWπteEnable Stall = WantToXfer AND (NOT TWπteEnable) SWnteEnable = NOT(Stall) If (SWnteEnable) Shift Register = Fetch 6 bits from EFSense[ReadBuffer] CurrAdr CurrAdr = CurrAdr + 640 XfersRemaining = XfersRemaining - 1 Endlf Until (TWnteEnable) EndFor Wait until BufferEF Wnte process has finished EFSense = NOT (EFSense) While read process is transfemng data from E or F to the PHI, a wnte process is prepanng the next dot-line in the other buffer The data being wπtten to E or F is color 1 data generated by the HCU, and color 2-6 data from buffer D (supplied from DRAM) Color 1 data is wπtten to EF whenever the HCU's OutputValid flag is set, and color 2-6 data is wπtten during other times from register C Buffer OE, 81 in FIG 9 is a 32-bit register used to hold a single HCU-generated set of contiguous 32 dots for color 1 While the dots are contiguous on the page, the odd and even dots are pnnted at different times Buffer AB 82 is a double buffered mechanism for delaying odd dot data for color 1 by 2 dothnes Buffers A and B therefore have identical structures Dunng the processing of a line of dots, one of the two buffers is read from and then wntten to The two buffers are logically swapped after the entire dot line has been processed A single bit flag ABSense determines which of the two buffers are read from and wπtten to The HCU provides 32-bits of color 1 data whenever the output valid control flag is set, which is every 32 cycles after the first flag has been sent for the line The 32 bits define a contiguous set of 32 dots for a single dot line - 16 even dots (bits 0, 2, 4 etc ), and 16 odd dots (bits 1, 3, 5 etc ) The output valid control flag is used as a WπteEnable control for the OE, register 81 We process the HCU data every 2 OutputValid signals The 16 even bits of HCU color 1 data are combined with the 16 even bits of register OE, to make 32-bits of even color 1 data Similarly, the 16 odd bits of HCU color 1 data are combined with the 16 odd bits of register OE, to make 32-bits of odd color 1 data Upon receipt of the first OutputValid signal of the group of two, we read buffer AB to transfer the odd data to color 1 , 73 in FIG 11 within buffer EF Upon receipt of the second OutputValid signal of the group of two, we wnte the 32-bits of odd data to the same location in buffer AB that we read from previously, and we wnte the 32-bits of even data to color 1 within buffer EF The HCU provides 32 bits of data per color plane whenever the OutputValid control flag is set This occurs every 32 cycles except dunng certain startup times The 32 bits define a contiguous set of 32 dots for a single dot line - 16 even dots (bits 0, 2, 4 etc ), and 16 odd dots (bits 1, 3, 5 etc ) While buffer OE, (83 in FIG 10) is used to store a single 32-bit value for color 1, buffers OE 2 to OE 6 are used to store a single 32-bit value for colors 2 to 6 respectively Just as the data for color 1 is split into 32-bits representing color 1 odd dots and 32-bits representing color 1 even dots every 64 cycles (once every two OutputValid flags), the remaining color planes are also split into even and odd dots However, instead of being wπtten directly to buffer EF, the dot data is delayed by a number of lines, and is wntten out to DRAM via buffer CD (84 in FIG 9) While the dots for a given line are wntten to DRAM, the dots for a previous line are read from DRAM and wπtten to buffer EF (71,72) This process must be done interleaved with the process writing color 1 to buffer EF Every time an OutputValid flag is received from the HCU on line 85 in FIG 10, the 32-bits of color N data are wπtten to buffer OE N (83) Every second OutputValid flag, the combined 64-bit value is wπtten to color buffer N (86) This happens in parallel for all color planes 2-6 Color Buffer N (86) contains 40 sets of 64-bιts (320 bytes) to enable the dots for two complete segments to be stored This allows a complete segment generation time (20 x 64 = 1280 cycles) for the previous segment's data (both odd and even dots) to be wπtten out to DRAM Address generation for wnting is straightforward The ColorNWnteEnable signal on line 87 is given every second OutputValid flag The address starts at 0, and increments every second OutputValid flag until 39 Instead of advancing to 40, the address is reset to 0, thus providing the double-buffeπng scheme This works so long as the reading does not occur dunng the OutputValid flag, and that the previous segment's data can be written to DRAM in the time it takes to generate a single segment's data The process is shown in the following pseudocode adr = 0 firstEncountered = 0 While (NOT AdvanceLine) If (HCU_OutputValιd) AND (firstEncountered)) ColorNWnteEnable = TRUE ColorNAdr = adr If (adr == 39) adr = 0 Else adr = adr + 1 Endlf Else ColorNWnteEnable = FALSE Endlf If (HCU_OutputValιd) firstEncountered = NOT(firstEncountered) Endlf EndWhile Address generation for reading is tπckier, since it is tied to the timing for DRAM access (both reading and wnting), buffer EF access, and therefore color 1 generation It is more fully explained below Address generation for buffers C, D, E, F, and colorN are all tied to the timing of DRAM access, and must not interfere with color 1 processing with regards to buffers E and F The basic pnnciple is that the data for a single segment of color N (either odd or even dots) is transferred from the DRAM to buffer EF via buffer CD Once the data has been read from DRAM those dots are replaced based on the values in ColorBufferN This is done for each of the colors in odd and even dots After a complete segment's worth of dots has accumulated (20 sets of 64 cycles), then the process begins again Once the data for all segments in a given pπntline has been transferred from and to DRAM, the current address for that color's DRAM buffer is advanced so that it will be the appropnate number of lines until the particular data for the color's line is read back from DRAM In this respect then, the DRAM acts as a form of FIFO Consequently color N (either odd or even) is read from DRAM into buffer D while copying color N (same odd/even sense) to buffer C The copying of data to buffer C takes 20 or 21 cycles depending on whether the OutputValid flag occurs during the 20 transfers Once both tasks have finished (typically the DRAM access will be the slower task), the second part of the process begins The data in buffer C is wπtten to DRAM (the same locations as were just read) and the data in buffer D is copied to buffer EF (again, no color N data is transferred to buffer EF while the OutputValid flag is set since color 1 data is being transferred) When both tasks have finished the same process occurs for the other sense of color N (either odd or even), and then for each of the remaining colors The entire double process happens 10 times The addresses for each of the current lines in DRAM are then updated for the next line's processing to begin In terms of bandwidth, the DRAM access for dot data buffers consumes the great majoπty of all DRAM access from PEC For each pπnt line we read an entire dot line for colors 2-6, and wnte an entire dot line for colors 2-6 For the maximum of 15 segments this equates to 2 x 5 x 15 x 1280 bits = 192,000 bits (24,000 bytes) per pnnt line For the fastest printing system (30,000 lines per second) this equates to 687 MB/sec For 1 page per second pπnting the bandwidth required is 312 MB/sec Since the bandwidth is so high, the addresses of the vaπous half-lines for each color in DRAM should be optimized for the memory type being used In an RDRAM memory system for example, the very first half-line buffer is aligned for each color to a 1KByte boundary to maximize page-hits on DRAM access As the vaπous segments are processed it is necessary to ensure that if the start of the next segment was going to be aligned at byte 960 within the 1KByte page, then the 640-bit access would span 2 pages Therefore the variable DRAMMaxVal is used to check for this case, and if it occurs, the address is rounded up for the next half-line buffer to be page-aligned Consequently the only waste is 64 bytes per 13 segments, but have the advantage of the 640-bit access completely within a single page The address generation process can be considered as NumSegments worth of 10 sets of 20 x 32-bιt reads followed by 20 x 32-bit wπtes, and it can be seen in the following pseudocode EFStartAdr = 0 Do NumSegments times For CurrColor = 0 to MaxHalfColors DRAMStartAddress = ColorCurrAdr[CurrColor] While reading 640 bits from DRAMStartAddress into D(>= 20 cycles) ColorNAdr = 0 While (ColorNAdr '= 20) If (NOT HCUJDutputVahd) Transfer ColorNBuffer[ColorNAdr|CurrColor_bιtO] to C[ColorNAdr] ColorNAdr = ColorNAdr + 1 Endlf EndWhile EndWhile - wait until read has finished While writing 640 bits from C into DRAMStartAddress (>=20 cycles) ColorNAdr = 0 EFAdr = EFStartAdr While (ColorNAdr '= 20) If (NOT HCU_OutputValιd) Transfer D[ColorNAdr] to EF[CurrColor|EFAdr] If ((ColorNAdr == 19) AND (CurrColor == NumHalfColors)) EFStartAdr = EFAdr + 1 Else EFAdr = EFAdr + 1 Endlf ColorNAdr = ColorNAdr + 1 Endlf EndWhile EndWhile - wait until write has finished If (DRAMStartAddress == DRAMMaxVal) ColorCurrAdrfcurrColor] = round up DRAMStartAddress to next 1KByte page Else ColorCuπAdr[cuπColor] = DRAMStartAddress + 640 bits Endlf If (Segment == maxSegments) If (ColorCurrRow[CurrColor] = ColorMaxRow[CurrColor]) ColorCurrRow[cuπColor] = ColorStartRow[currColor] ColorCurrAdrfcurrColor] = ColorStartAdr[currColor] Else ColorStartRow[currColor] = ColorCurrRow[currColor] + 1 Endlf Endlf EndFor EndDo Wait until next Advance signal from PHI Note that the MaxHalfColors register is one less than the number of colors in terms of odd and even colors treated separately, but not including color 1 For example, in terms of a standard 6 color pnnting system there are 10 (colors 2-6 in odd and even), and so MaxHalfColors should be set to 9 The LLFU requires INumSegments cycles to prepare the first 180 bits of data for the PHI Consequently the pnnt head should be started and the first LineSync pulse must occur this penod of time after the LLFU has started This allows the initial Transfer value to be valid and the next 90-bit value to be ready to be loaded into the Transfer register The print head interface (PHI) is the means by which the processor loads the pπnt head with the dots to be pπntcd, and controls the actual dot pπnting process It takes input from the LLFU and outputs data to the pnnt head itself The PHI will be capable of dealing with a vanety of pπnt head lengths and formats The internal structure of the PHI should allow for a maximum of 6 colors, 8 segments per transfer, and a maximum of 2 segment groups This should be sufficient for a 15 segment (8 5 inch) pπnter capable of printing A4/Letter at full bleed Throughout the specification the aim has been to descnbe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features Persons skilled in the art may realize variations from the specific embodiments that will nonetheless fall within the scope of the invention

Claims: CLAIMS A pπnt engine/controller to dπve an ink drop print head compπsing an interface at which to receive compressed page data, decoders to decode respective types of image planes in the received compressed page data, and a half-toner/compositor to composite image plane data, the half-toner/compositor including a dot merger unit taking bits from the respective planes as inputs, and a color mask register holding masking bits in number equal to the number of image planes, respective input bits to the dot merger unit being ANDed with respective color mask register bits and the resultant bits ORed together to form an output bit in a channel for which there is an ink at the pπnt head A pπnt engine/controller as claimed in claim 1 wherein the respective planes to the dot merger unit include three contone color planes and a high resolution plane and the color mask register is loaded with bits that are selected to place the high resolution plane into any one of the respective color channels A pπnt engine/controller as claimed in claim 2 wherein a fixative channel is generated from any one or more of the respective planes and selected by what bits are loaded to the color mask register A pπnt engine/controller as claimed in claim 1 wherein the color mask register is loaded with bits that are selected to split a K plane into C, M, and Y channels for output to a pπnt head without K A print engine/controller as claimed in claim 1 wherein the half-toner compositor includes a tag encoder generating an infrared tag data plane and the color mask register maps its dots into an infrared channel at the pπnt head A pπnt engine/controller to dπve an k drop pπnt head compπsing a contone image decoder to decode any compressed continuous tone image planes in the received compressed page data, a high resolution image decoder to decode any compressed high resolution image plane, and a halftoner/compositor including a dot merger unit controlled by a color mask to map image planes into channels corresponding to what inks are supplied in the pπnt head that is interfaced by the pπnt engine/controller A pnnt engine/controller to dπve an ink drop pnnt head compnsing a contone image decoder to decode any compressed continuous tone image planes in the received compressed page data, a high resolution decoder to decode any compressed high resolution image plane, and a halftoner/compositor including a margin unit to apply margin data to the respective image planes dunng the composite process, and a dot merger unit controlled by a color mask to map image planes into channels corresponding to what inks are supplied in the pπnt head that is interfaced by the pπnt engine/controller A pπnt engine/controller chip to interface with an ink drop pπnt head compπsing an interface at which to receive compressed page data, a contone image decoder to decode any continuous tone image planes in the received compressed page data, a high resolution decoder to decode any high resolution image plane in the received compressed page data, a half-toner/compositor including to dither any continuous tone image planes and composite any high resolution image plane data with any output plane including a dot merger unit controlled by a color mask to map image planes into channels corresponding to what inks are supplied in the pnnt head that is interfaced by the pnnt engine/controller, and a pπnt head dπver to output the composite to a pπnt head An ink drop pπnter dnven by a pπnt engine/controller compπsing an interface at which to receive compressed page data, a contone image decoder to decode any continuous tone image planes in the received compressed page data, a high resolution image decoder to decode any high resolution image planes in the received compressed page data, a half-toner/compositor to dither any continuous tone image planes and composite high resolution image plane data with any output plane including a dot merger unit controlled by a color mask to map image planes into channels corresponding to what inks are supplied in the pπnt head that is interfaced by the pπnt engine/controller, and a print head dπver to output the composite to a pnnt head, and a pnnt head A method of operating an ink drop pnnter comprising receiving compressed page data decoding any continuous tone image planes in the received compressed page data to generate output planes, decoding any high resolution image plane in the received compressed page data to generate an output plane, ditheπng any continuous tone image planes, compositing any high resolution image plane data with any output plane, and forwarding composited data to a pnnt head with image planes mapped to what inks are available at the pnnt head

Inventors: WALMSLEY SIMON ROBERT, WALMSLEY, SIMON, ROBERT
Applicants: SILVERBROOK RES PTY LTD, WALMSLEY SIMON ROBERT, SILVERBROOK RESEARCH PTY LTD, WALMSLEY, SIMON, ROBERT
Application year: 2000
Main classification: B41J2
IPC codes: B41J2, G06K15, G06T5, H04N1