AU2008258182A1 - Sub-scanline colour conversion buffering - Google Patents

Description

S&F Ref: 888755 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address Canon Kabushiki Kaisha, of 30-2, Shimomaruko 3 of Applicant: chome, Ohta-ku, Tokyo, 146, Japan Actual Inventor(s): David Karlov Craig William Northway Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Sub-scanline colour conversion buffering The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(1 897007_1) SUB-SCANLINE COLOUR CONVERSION BUFFERING FIELD OF INVENTION The current invention relates to the colour conversions performed by printers and other visual output devices and, in particular, to treatment of rendering intent. 5 DESCRIPTION OF BACKGROUND ART A colour conversion is the mapping of a colour from one colour space to another colour space. A colour space provides a way of mathematically representing different colours, often in the form of n-tuples of numbers. Different colour spaces have different uses. For example, the RGB colour space describes what type of light needs to be emitted to produce a specific 0 colour. Visual output devices, such as computer monitors, may use RGB or a similar colour space. The CMYK colour space is used to describe what kinds of inks need to present on a surface so that light reflected from that surface is a specific colour. The need for colour space conversion is then apparent. For example, there may be an image displayed on a computer monitor using the RGB colour space that is then printed onto a page using the CMYK colour 5 space. A colour space conversion is required for this to occur. Typically, a gamut mismatch occurs between two colour spaces involved in a colour conversion. The term gamut refers to a set of colours represented in a colour space. A gamut mismatch is a problem when one or more colours are represented in an input colour space but not in the output colour space. It is not always clear what colour a specific colour in the input 0 colour space should map to in the output colour space. A rendering intent makes it possible to specify a method of conversion to use when a gamut mismatch occurs. Four common rendering intents are: relative colorimetric, absolute colorimetric, perceptual and saturation. Each rendering intent is useful in a certain application. For instance, a viewer of a photo is more concerned with the relative difference between colour values of colours in an image than !5 the exact value of the colours in the image. Typically, a photo is colour converted using the perceptual rendering intent. The perceptual rendering intent is a gamut mapping that maintains relative difference between colour values of the colours in the image. It is desirable to try to preserve, as much as possible, the exact colour values of the colours in the image. The absolute colorimetric rendering intent allows this to be specified. The 30 absolute colorimetric rendering intent maps a colour in one colour space to the closest colour in the target colour space without any regard to relative difference between the colours in the image. Other rendering intents have similar well-defined applications. 1894447vl(888755_Final) -2 Typically a conventional raster image processing system receives graphics source data containing a number of different objects each with their own specified rendering intent. The colour conversion of each of the objects will take place based on a specified rendering intent. An alternative scenario occurs in order to correctly render custom filter effects. In this scenario, the graphics source data is a pre-rendered bitmap composed from multiple input objects. Sometimes this pre-rendering step occurs using a render colour space that is different to the render colour space to be used when rendering the pre-rendered bitmap together with other graphics source data. In this case, the pixels of the pre-rendered bitmap need to be colour converted to another colour space, and each pixel of the pre-rendered bitmap has a rendering intent associated with the pixel. Each pixel is then separately colour converted with a colour conversion apparatus being setup prior to each colour conversion based on the rendering intent of the pixel. Such a method has several drawbacks. One is that the required setup of the colour conversion apparatus for each pixel in the page significantly increases the time taken to process the page. This represents a significant disadvantage as the 5 competitiveness of a raster image processing system is dependent on its speed. SUMMARY OF THE INVENTION It is an object of the present invention to substantially overcome, or at least ameliorate, one or more disadvantages of existing arrangements. ) According to one aspect of the present invention there is provided a method of performing a colour space conversion of an image, wherein each pixel of the image has a plurality of metadata, said method comprising the steps of: determining a run of contiguous pixels which share at least one of the plurality of metadata; and 25 performing the colour space conversion of the run of contiguous pixels, based on the at least one of the plurality of metadata, wherein the run of contiguous pixels comprises a plurality of pixels where the plurality of pixels in the run share the at least one of the plurality of metadata. 1894447vl(888755_Final) -3 According to another aspect of the present invention there is provided an apparatus for performing a colour space conversion of an image, wherein each pixel of the image has a plurality of metadata, said apparatus comprising: means for determining a run of contiguous pixels which share at least one of the plurality of metadata; and means for performing the colour space conversion of the run of contiguous pixels, based on the at least one of the plurality of metadata, wherein the run of contiguous pixels comprises a plurality of pixels where the plurality of pixels in the run share the at least one of the plurality of metadata. According to still another aspect of the present invention there is provided a system for performing a colour space conversion of an image, wherein each pixel of the image has a plurality of metadata, said system comprising: a memory for storing data and a computer program; and 5 a processor coupled to the memory for executing the computer program, the computer program comprising instructions for: determining a run of contiguous pixels which share at least one of the plurality of metadata; and performing the colour space conversion of the run of contiguous pixels, based 0 on the at least one of the plurality of metadata, wherein the run of contiguous pixels comprises a plurality of pixels where the plurality of pixels in the run share the at least one of the plurality of metadata. According to still another aspect of the present invention there is provided a computer 25 readable medium having a computer program stored thereon, said computer program being 1894447vl (888755_Final) -4 configured for performing a colour space conversion of an image, wherein each pixel of the image has a plurality of metadata, said computer program comprising: code for determining a run of contiguous pixels which share at least one of the plurality of metadata; and code for performing the colour space conversion of the run of contiguous pixels, based on the at least one of the plurality of metadata, wherein the run of contiguous pixels comprises a plurality of pixels where the plurality of pixels in the run share the at least one of the plurality of metadata. Other aspects of the invention are also disclosed. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described with reference to the following drawings, in which: Fig. I is a flow chart of a method for colour conversion of a scan line of pixels; Fig. 2 is a flowchart for a method of rendering custom filter effects; 5 Fig. 3 is a schematic block diagram of a render pipeline in which rendering arrangements of the present disclosure may be implemented; Fig. 4 is a schematic block diagram of a computer system incorporating a rendering arrangement; Fig. 5 is a flow chart of a method of rendering graphical objects requiring a post-render 0 colour conversion; and Fig. 6 is a flow chart of a method of rendering graphical objects requiring a during-render colour conversion. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION A raster image processing (RIP) system converts vector graphics input data into pixel !5 graphics output data. The vector graphics input data is typically written in one of many known Page Description Languages (PDLs), and the output pixel data is often of a format and bit depth suitable for a printing device to directly print onto a physical medium. It is advantageous to design RIP software in multiple software layers to improve software reusability. A common feature of RIP software architectures is the separation of a 30 PDL Interpreter and a Renderer. The PDL Interpreter converts PDL input data into an 1894447v1(888755_Final) -5 intermediate graphics data format understood by a Renderer, and the Renderer takes the intermediate graphics data and produces pixels. The source of the PDL data is typically one of many computer applications. Some of these applications allow graphical artists to manipulate graphics using advanced methods. One such advanced method is a filtering effect which is applied to a set of objects after the objects are composited together. While the PDL representation of these filter effects must always be understood by the PDL Interpreter, sometimes these filter effects include custom processing which is not natively understood by the Renderer. One method employed by pixel sequential renderers to correctly render custom filtering effects involves first rendering a set of objects to be filtered into a buffer, and then passing contents of the buffer back to the PDL Interpreter as pixels. The PDL Interpreter applies the filter effect to the contents of the buffer, and hands the result back to the Renderer to include in the drawing. The PDL interpreter is often required to perform a colour conversion before returning the buffer to the Renderer. 5 Fig. 4 shows a system 400 for processing computer graphic images. The system 400 includes a host processor 402 associated with system 400, random access memory (RAM) 403, which may include a non-volatile hard disk drive 405 or similar device and volatile, semiconductor RAM 404. The system 400 also comprises a system read-only memory (ROM) 406 typically found with semiconductor ROM 407 and which in many cases may be 3 supplemented by compact disk devices (CD ROM) 408. The system 400 may also comprise a target device 311 for displaying images, which may be a printer or video display unit (VDU) which operates in raster fashion. The above-described components of the system 400 are interconnected via a bus system 409 and are operable in a normal operating mode of computer systems well known in !5 the art, such as IBM PC/AT type personal computers and arrangements evolved therefrom. The processes of Figs. 1, 2, 5 and 6, to be described below, may be implemented as one or more software application programs executable within the system 400. In particular, the steps of the described methods may be effected by instructions in the software that are carried out within the system 400. The software instructions may be formed as one or more 30 code modules, each for performing one or more particular tasks. The software may also be divided into two separate parts, in which a first part and the corresponding code modules 1894447vI(888755_Final) -6 performs the described methods and a second part and the corresponding code modules manage a user interface between the first part and the user. The software may be stored in a computer readable medium, including the storage devices described below, for example. The software is loaded into the system 400 from the computer readable medium, and then executed by the system 400. A computer readable medium having such software or computer program recorded on it is a computer program product. The use of the computer program product in the system 400 preferably effects an advantageous apparatus for implementing the described methods. In some instances, the application programs may be supplied to the user encoded on ) one or more CD-ROM and read via a corresponding drive. Still further, the software can also be loaded into the system 400 from other computer readable media. Computer readable storage media refers to any storage medium that participates in providing instructions and/or data to the system 400 for execution and/or processing. Examples of such storage media include floppy disks, magnetic tape, CD-ROM, a hard disk drive, a ROM or integrated circuit, 5 USB memory, a magneto-optical disk, or a computer readable card such as a PCMCIA card and the like, whether or not such devices are internal or external of the system 400. Examples of computer readable transmission media that may also participate in the provision of software, application programs, instructions and/or data to the system 400 include radio or infra-red transmission channels as well as a network connection to another computer or ( networked device, and the Internet or Intranets including e-mail transmissions and information recorded on Websites and the like. The second part of the application programs and the corresponding code modules mentioned above may be executed to implement one or more graphical user interfaces (GUIs) to be rendered or otherwise represented upon a display (e.g., 311). Through manipulation of !5 typically a keyboard and mouse, a user of the system 400 and the application may manipulate the interface in a functionally adaptable manner to provide controlling commands and/or input to the applications associated with the GUI(s). Also seen in Fig. 4, a graphic rendering module 303 (or renderer) connects to the bus 409, and is configured for the rendering pixel-based images derived from graphic object-based 30 descriptions supplied with instructions and data from the processor 402 via the bus 409. The renderer 303 may utilise the system RAM 403 for the rendering of object descriptions 1894447vl(888755_Final) -7 although preferably the renderer 303 may have associated therewith a dedicated rendering store arrangement 330, typically formed of semiconductor RAM. The rendering module 303 may be implemented as software executing on the host processor 402, or the rendering module 303 may be an embedded system on the target device 1 311. In one embodiment, the rendering module 303 may be a separate self-contained hardware module. An implementation of a rendering pipeline 300 for such a rendering module 303 is shown in Fig. 3.Referring now to Fig.3, a graphics data source 301, such as a PDL (page description language) interpreter or GDI (graphics device interface) driver, running on the host processor 402, sends graphics data to the graphics rendering system 302. The graphics rendering system 302 has a display list generation module 305 and the rendering module 303. The display list generation module 305 generates a display list from a set of objects defined in the data received from the graphics data source 301. Objects in the display list are ordered in z-level (priority) order from a lowest-priority object to a highest priority object. 5 The display list is stored in the display list store 306. The rendering module 303 processes the display list, generating a bitmap, which may be halftoned, for printing. In the case that the renderer 303 is resident as software on the host computer 400, the renderer 303 generates a bitmap, which may be half-toned. The bitmap is compressed and sent to the target device 311, which decompresses the bitmap and renders the page of pixel data. ) In an alternative configuration, the display list generation module 305 resides on the host computer 400 and the rendering module 303 is embedded in the target device 311. In this case, the host processor 402 sends the display list to the target device 311, which renders the display list and generates pixel data for printing. The rendering module 303 may use any suitable rendering method which supports the operations specified in the display list such as !5 compositing. The graphics data source 301, which may be a PDL interpreter, receives graphics data that may include graphics to which are applied custom filter effects that are not understood by the graphics rendering module 303. Referring now to Fig. 2, a method 200 of rendering custom filter effects, will now be described. The method 200 may be implemented as 30 software resident on the HDD 405 and being controlled in its execution by the processor 402. The graphics data source 301 will in this scenario send the graphics to the graphics rendering system 302 for pre-rendering at step 201. The graphics rendering system 302 will then render 1894447v1 (888755_Final) -8 an image in step 202 and then return the image to the graphics data source 301 as a set of pixels at step 203. In step 204 the image is colour converted by the graphics data source. Step 204 is performed on a scan line by scan line basis as described below in reference to Fig. 1. Following colour conversion, the image is sent to the graphics rendering system 302 at step i 205 so that the image may be further processed and combA method 100 of performing a colour space conversion of a scan line of pixels (e.g., pixels of an image), as executed at step 204, will now be described with reference to Fig. 1. Each of the pixels has a plurality of metadata. The metadata comprises attribute data as part of an attribute bitmap. The metadata for a pixel comprises (or indicates) rendering intent of the pixel. ) The method 100 may be implemented as software resident on the HDD 405 and being controlled in its execution by the processor 402. The method 100 receives the scanline of pixels from a graphics data source, such as a PDL interpreter 301. The metadata of the first pixel in the scan line is examined by the processor 402 at step 102 for determining the rendering intent of the current pixel. In step 103 the rendering intent of the current pixel being 5 examined is stored, for example, in the system RAM 403. At step 104, if the processor 402, determines that there are any more pixels remaining in the scanline, then the method 100 proceeds to step 105. Otherwise, the method 100 proceeds to step 107. At step 105, the next pixel in the scanline is examined. Following step 105, at step ) 106, the processor 402 compares the rendering intent of the current pixel being examined and the rendering intent stored in step 103. If the two rendering intents are the same, then the method 100 returns to step 104. This step produces a contiguous run of pixels which share the same rendering intent (i.e., the plurality of pixels in the run share at least one of the plurality of metadata). Thus, instead of performing the colour conversion on a per pixel basis, the ?5 colour conversion is performed on the contiguous run. This means that adjacent pixels with the same rendering intent are colour converted together, thus speeding up the colour conversion process. If the two rendering intents are different, then the method 100 proceeds to step 107 where a colour conversion apparatus is setup based on the rendering intent stored at step 104. Then at step 108 the colour conversion apparatus converts the pixels in the scan line 30 from the last pixel examined at step 103 to and including the previous pixel that was examined that has the same rendering intent as the last pixel examined at step 103. 1894447v1(888755_Final) -9 In step 109, the processor 402 determines if there are any pixels remaining in the scanline that have yet to be colour converted. If there are more pixels remaining in the scanline then the method 100 moves to step 103. If there are no more pixels remaining in the scanline (i.e., all pixels in the scanline have been colour converted), then the method 100 ends. One will recognise that the role rendering intent plays in Fig.1 may be replaced by any type of pixel metadata that contains information, or from which information can be deduced, that determines how a pixel should be colour converted. An example of this is pixel by pixel attributes that are found with an attribute bitmap. ) Several alternative embodiments will now be described. Each alternative is described as a variation of the methods described above, and may be implemented in parallel with any other alternative, or implemented alone. In one alternative embodiment, a post-render colour conversion may be used. The graphics data source 301, which may be a PDL interpreter, receives graphics data. Referring now to Fig. 5, a method 500 of rendering graphical objects requiring a during-render colour conversion, will now be described. Again, the method 500 may be implemented as software resident on the HDD 405 and being controlled in its execution by the processor 402. The method 500 begins at step 501, where the PDL interpreter processes the graphics data into a form that is understandable by the graphics renderer 302. The processed data is ) then sent to the graphics renderer 302 at step 502. In step 503 a display list is generated from the received processed data. Step 503 is achieved using the display list generation module 305. In step 504 the display list 306 is rendered into pixels by the rendering module 303. The rendering module 303 then colour converts the pixels in step 505 with reference to Fig. 1. The colour converted pixels are then sent to the target device at step 506. 5 In another embodiment, the graphics renderer 302 will, during the rendering process, perform a colour conversion. This occurs if a subset of the graphics data must be composited together in a specified render colour space before being combined with the other graphics data in the main render colour space. With reference to Fig. 6, a method 600 of rendering graphical objects requiring a 0 during render colour conversion, will now be described. The method 600 is implemented by the Rendering module 303. The Rendering module 303 receives the set of objects at step 601 and renders the set of objects into pixels at step 602. The Rendering module 303 then converts 1894447vl(888755_Final) -10 the pixels from a sub-render colour space into a main render colour space in step 603 with reference to Fig.1. The pixels are then composited with other rendered objects, if any, as part of the rendering process at step 604. The rendering process then continues. Industrial Applicability 5 The arrangements described are applicable to the computer and data processing industries and particularly for the image processing. The foregoing describes only some embodiments of the present invention, and modifications and/or changes can be made thereto without departing from the scope and spirit of the invention, the embodiments being illustrative and not restrictive. ) In the context of this specification, the word "comprising" means "including principally but not necessarily solely" or "having" or "including", and not "consisting only of'. Variations of the word "comprising", such as "comprise" and "comprises" have correspondingly varied meanings. 1894447vl(888755_Final)

Claims (7)

1. A method of performing a colour space conversion of an image, wherein each pixel of the image has a plurality of metadata, said method comprising the steps of: determining a run of contiguous pixels which share at least one of the plurality of metadata; and performing the colour space conversion of the run of contiguous pixels, based on the at least one of the plurality of metadata, wherein the run of contiguous pixels comprises a plurality of pixels where the plurality of pixels in the run share the at least one of the plurality of metadata.

2. A method of claim 1, wherein the metadata comprises attribute data as part of an attribute bitmap.

3. A method of claim 1, wherein the metadata comprises rendering intent.

4. An apparatus for performing a colour space conversion of an image, wherein each pixel of the image has a plurality of metadata, said apparatus comprising: 0 means for determining a run of contiguous pixels which share at least one of the plurality of metadata; and means for performing the colour space conversion of the run of contiguous pixels, based on the at least one of the plurality of metadata, wherein the run of contiguous pixels comprises a plurality of pixels where the plurality of pixels in the run share the at least one of 5 the plurality of metadata. 1894447v I(888755_Final) - 12

5. A system for performing a colour space conversion of an image, wherein each pixel of th image has a plurality of metadata, said system comprising: a memory for storing data and a computer program; and a processor coupled to the memory for executing the computer program, the computer 5 program comprising instructions for: determining a run of contiguous pixels which share at least one of the plurality of metadata; and performing the colour space conversion of the run of contiguous pixels, based on the at least one of the plurality of metadata, wherein the run of contiguous pixels ) comprises a plurality of pixels where the plurality of pixels in the run share the at least one of the plurality of metadata.

6. A computer readable medium having a computer program stored thereon, said computer program being configured for performing a colour space conversion of an image, wherein 5 each pixel of the image has a plurality of metadata, said computer program comprising: code for determining a run of contiguous pixels which share at least one of the plurality of metadata; and code for performing the colour space conversion of the run of contiguous pixels, based on the at least one of the plurality of metadata, wherein the run of contiguous pixels comprises 0 a plurality of pixels where the plurality of pixels in the run share the at least one of the plurality of metadata.

7. A method of performing a colour space conversion of an image, wherein each pixel of the image has a plurality of metadata, said method being substantially as herein before described 1894447v1 (888755_Final) - 13 with reference to any one of the embodiments as that embodiment is shown in the accompanying drawings. DATED this 17th Day of December 2008 CANON KABUSHIKI KAISHA Patent Attorneys for the Applicant SPRUSON&FERGUSON 1894447vl(888755_Final)