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

Michael Sweet msweet at msweet.org
Fri May 28 12:59:13 UTC 2021


Till,

> On May 27, 2021, at 2:04 PM, Till Kamppeter <till.kamppeter at gmail.com> wrote:
> ...
> If I look into the source code of the pclmtoraster filter of cups-filters (cupsfilters/pclmtoraster.cxx) I see that when readin the embedded bitmaps from a PDF file there only occur /DeviceGray, /DeviceRGB, and /DeviceCMYK color spaces. How do I determine whether I have sRGB or AdobeRGB? Vikrant?Ans what is the default/IPP/PWG-standard color space of /DeviceCMYK?

Assume sRGB/sGray - pclm was intended as a format for entry-level HP laser printers. DeviceCMYK is CUPS_CSPACE_CMYK (no associated profile, always a device color space).

> Also, if I have images (JPEG, TIFF, PNG, ...) how do I know which coloe space they are? imagetoraster seems not to determin whether images are sRGB or AdobeRGB.

EXIF (used for both JPEG and TIFF) includes several tags related to color space, starting with ColorSpace (sRGB or "other") and then using PrimaryChromaticities (sic) for the "other" color space to match it with the AdobeRGB primaries.

	https://www.jeita.or.jp/cgi-bin/standard_e/list.cgi?cateid=1&subcateid=4

For PNG you need to look at the cHRM chunk to compare primaries:

	https://datatracker.ietf.org/doc/html/rfc2083#page-20

If the file doesn't have this chunk, assume sRGB.

________________________
Michael Sweet





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