Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1996-01-10
1998-10-27
Coles, Edward L.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358534, 358536, H04N 146
Patent
active
058288155
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Field of the Invention
The present invention relates to a method for printing digital colour images on hard copy and is intended in particular for use in desktop or graphical applications like electronic printing, copying and colour proofing.
2. Background of the Invention
The last few years, electrophotography has made two important evolutions. First of all the ability to fix on paper coloured toners on top of each other, opened the way to make printed hard copies of colour images. Secondly the increased number of density levels for one printed dot, started the move from binary printing to multilevel (4, 8, 16 levels) or almost continuous tone (64, 128, 256 levels) printing. One of the most performing high-resolution colour scanner/printer/copier systems on the market is the AGFA XC305 and AGFA XC315 system. This system uses eight bit data for every printed dot for each of the subtractive colour components (Cyan, Magenta, Yellow and blacK : CMYK). Every printed dot on printed matter can thus get theoretically 256 different density levels for each colour component C, M, Y and K. Although some printers based on electrophotographic printing technology claim to be able to represent 256 different density levels per colour on one printed dot, this is an overstatement. Printers with an addressability of 400 dpi (dots per inch) can effectively achieve 64 and exceptionally up to 128 different density levels per printed dot. For that reason said copier uses a screening technique, even when operating fully in eight bit mode. It is known that printed matter with a screen ruling of 200 lpi (lines per inch) and 128 grey levels can render high quality images.
Together with a spatial resolution of 400 dpi (dots per inch) for the individual printed dots, this system is able to deliver high quality colour copies. These copies can be used for short-run colour, i.e. small amounts of coloured copies ; and for Direct Digital Colour Proofing (DDCP), i.e. checking the colour output of a reproduction on another system.
The printer/copier can be used in direct colour copy mode. In that case, the original colour document is scanned four times, for each printing phase C, M, Y and K respectively. For every phase, the three additive colour components (Red, Green and Blue or RGB) of every pixel on the original copy are simultaneously quantified into 8 bit data and combined on the fly in the image manipulation unit within the copier to a signal representing the subtractive component C, M, Y or K to be printed on the copy. This process poses no big intermediate storage requirements, because the scanning speed is chosen to be conform with the processing speed of the processor means in the image manipulation unit to combine the RGB signals to the C, M, Y or K signals and the printing speed for the electrophotographic process. Said processor means does not have to buffer or store large portions of the image to be copied. Memory means for buffering two scanned lines will suffice in most cases.
Another feature of this type of printer/copier is that a colour image in electronic representation format can be downloaded to the colour printing system. This offers the possibility to connect it to a Raster Image Processor (RIP). A RIP is an electronic device that converts a Page Description Language (PDL) in a colour bitmap. For binary black-and-white printing systems, a simple bitmap storing one bit of information per printed dot is enough. In colour output systems, one bitmap per colour component is necessary. In multilevel systems, the bitmap needs more than one bit of information per printed dot. A bitmap contains the signals that can be stored in memory means like DRAM (Dynamic Random Access Memory) making a printed-dot-wise representation for the image to be printed on the hard copy.
Said downloaded image can be formally described in terms of a PDL. AgfaScript (AgfaScript is a trade mark of Agfa-Gevaert A.G. in Leverkusen, Germany) and PostScript (PostScript is a trade mark of Adobe Systems Inc.) are examples of a PDL. A PDL of
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Baeten Roger
Herregods Marc
Noppen Geert
AGFA-GEVAERT
Coles Edward L.
Lee Cheukfan
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