[Printing-architecture] Make use of extended color spaces on IPP printers
msweet at msweet.org
Sun May 9 20:55:01 UTC 2021
> On May 9, 2021, at 4:14 PM, Till Kamppeter <till.kamppeter at gmail.com> wrote:
> But this would be the task of the renderer then. Does Ghostscript do this?
It might, but certainly not with the current CUPS driver.
>> Therefore, you can examine the embedded image objects (all of the current tools provide utilities for extracting them) as a hint to what color space might be best if you have to choose between AdobeRGB and sRGB.
> Yes, it is not a big problem to find all image objects, pclmtoraster does it for example. One could perhaps add a mode to this filter in which, instead of producing output, it tells hwther the input file is sRGB, AdobeRGB, or whatever.
> My questions:
> 1. Let us in the second use case assume that the t-Online logo is complete represented as vector graphics, like an SVG, but not necessarily in any standard format. How is its color defined then? An how the color space?
So there you would need to look at the PDF content stream or the page's dictionary (and its Resources array). Any resource object that has an array value with "/ICCBased" is an ICC color space, and the referenced object after the "/ICCBased" is the ICC profile. There are other ways that common profiles can be specified/approximated (e.g. "CalRGB" is approximately sRGB and "CalGray" is approximately sGray).
> 2. And how about a PDF with a mix of sRGB and AdobeRGB images? Should we produce the resulting (raster) page
> in AdobeRGB then as this has the wider gammut?
In general, yes. If there is also device RGB support and you have a profile, then *that* is your best color space.
>> That said, if you have a printer ICC profile and the printer supports device RGB (or device gray), then *that* is the best color space for the "last mile" to the printer.
> Then I could simply let Ghostscript apply it for the rasterization?
Yes, if you have a profile.
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