[Printing-architecture] Make use of extended color spaces on IPP printers

Michael Sweet msweet at msweet.org
Fri May 7 19:53:44 UTC 2021


> On May 7, 2021, at 2:52 PM, Till Kamppeter <till.kamppeter at gmail.com> wrote:
> TL;DR: Some doubts about supporting extended color depth and color spaces:
> - How to discover if a page in a PDF is 8/16-bit color/grayscale
>   sRGB/Adobe RGB?

So there are ways to do this, but none are pretty... :/

> - How important is Adobe RGB for printing? If a printer advertises that
>   it supports it, is it worthwhile for us to support jobs in Adobe RGB?

Very important, since a lot of cameras use AdobeRGB (or provide an option for it) for an expanded color gamut.  And if you are going from Display P3 (which is another one you'll see a lot of from iPhones/iPads) it is even more important since sRGB is a really small color space.

> - How is all this influenced by the "print-content-optimize" setting?

Two different things - certainly the 'photo' value might be hint that AdobeRGB/deep color is useful/important, but I'd also say that "print-quality" can also feature in this decision, e.g., 'high' (5) print quality might indicate deep color is preferred.

> I want to make it possible to make use of the support for extended color spaces of driverless IPP printers (or Printer Applications).
> IPP allows the user to only select from the following color modes for a job (list taken from PAPPL, actually available modes advertised in the
> "print-color-mode-supported" IPP attribute):
>  'auto'               - Automatic color/monochrome print mode
>  'auto-monochrome'    - Automatic monochrome/process mono print mode
>  'bi-level'           - B&W (threshold) print mode
>  'color'              - Full color print mode
>  'monochrome'         - Grayscale print mode using 1 color
>  'process-monochrome' - Grayscale print mode using multiple colors
> On mono/grayscale printers there is no 'auto-monochrome' and 'color'
> Printers support some extended color space modes, at least for raster input, as advertised in the "urf-supported" attribute for Apple Raster, and the "pwg-raster-document-type-supported" attribute for PWG Raster. The extensions are:
> - 16 bit per color instead of 8 bit per color in color or grayscale
> - Adobe RGB instead of sRGB in color

So print-color-mode and pwg-raster-document-type-supported/urf-support do two different things.  "print-color-mode" is a rendering intent (color, grayscale, bi-level, etc.) while the others list the actual color spaces and bit depths that are supported.

Michael Sweet

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