Help! What's matter with my raster data?

Horky Chen horky.chen at gmail.com
Wed Aug 16 09:13:37 PDT 2006


> Horky Chen wrote:
> >> Horky Chen wrote:
> >>> Dear all,
> >>>    I write one filter to package the raster data to our format. I use the CMYK color space, and color order is Chunked. When print one cyan color image,but the result I get via cupsRasterReadPixels cannot match the source data. For example, the color of my image is:
> >>>   C:0   M:79  Y:0  K:0, but I get from the Raster data, it be:
> >>>   C:34  M:67  Y:0  K:0!  That's why? Why I cannot get the real image data from CUPS Raster data?
> >> It is impossible to help you without more information.
> >>
> >> What operating system?
> >>
> >> What version of CUPS?
> >>
> >> What program are you using to produce the raster data used by your
> >> filter?
> >>
> >> --
> >> ______________________________________________________________________
> >> Michael Sweet, Easy Software Products           mike at easysw dot com
> >> Internet Printing and Document Software          http://www.easysw.com
> >
> > Dear Michael,
> >
> > Thanks for your quickly reply!
> >
> > I wrote the filter in Mac OS 10.4.7 and default CUPS enviroment. The source image is a TIFF file with Utagged CMYK profile and I print it with Photoshop 7.0. I have turned off the color management in Color Setting.
> >
> > How to get the real raster data?
>
> OK, so there are several things happening that will prevent it from
> working the way you expect.
>
> First, Photoshop (unfortunately) uses the pre-MacOS X print APIs
> which produce PICT files with embedded PostScript.  These are
> converted to PostScript using Apple's pictwpstops filter, then
> converted to PDF using Apple's pstopdffilter filter, and finally
> to CMYK raster data using Apple's cgpdftoraster filter.
>
> Second, IIRC the pstopdffilter will convert process your CMYK color
> data to a RGB colorspace, either the Generic RGB colorspace or your
> monitor's colorspace, depending on your colorsync settings.  The
> data is then converted back to CMYK by cgpdftoraster on the other
> end, either using Generic CMYK or a colorspace specified via the
> cupsICCProfile attribute in your driver's PPD file.
>
> Ultimately this means that you won't get raw CMYK data to your
> filter by printing from Photoshop.
>
> Apple also supplies an image filter (cgimagetoraster) which can
> print TIFF files and should do a better job of preserving colorspaces.
> You can test your driver with this filter by printing from the
> command-line using:
>
>      lp -d printername filename.tiff
>
> where "printername" is the queue name of the printer - run:
>
>      lpstat -p
>
> to see the queue names for your printers...
>
> Finally, you can get help from the Apple engineers by posting to
> the Apple printing list (lists.apple.com, then follow the links to
> subscribe...)
>
> --
> ______________________________________________________________________
> Michael Sweet, Easy Software Products           mike at easysw dot com
> Internet Printing and Document Software          http://www.easysw.com


That's great! Thank you very much.
I can get the real raster data now.
But I think it's will be a big trobule for us
to calibrate the image quality?

Anyway,Thanks for your help!





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