Subject: [IPP] Fwd: [Printing-architecture] pwgtoraster vs calibrated spaces

From: Ira McDonald <[email-masked]>
Date: Sat, 31 May 2014 10:46:31 -0400

Hi Mike,

>From Open Printing mailing list - apparent discrepancy in
PWG Raster spec definition for "sGray".

Please take a look at this.

Cheers,
- Ira

---------- Forwarded message ----------
From: James Cloos <[email-masked]>
Date: Sat, May 31, 2014 at 5:30 AM
Subject: [Printing-architecture] pwgtoraster vs calibrated spaces
To: [email-masked]

I was wrong about sGray.  It turns out that sGray is not defined as
having the same curve as sRGB, but rather it always has gamma 2.2.

The cupsraster document says srgb gamma/whitepoint, and the pwg raster
doc says srgb grayscale.  But everything else I've found says 2.2.
And it seems a D50 illuminate.

That being said, this colorspace dictionary:

[ /CalGray
  <<  /WhitePoint [ 0.96420288 1.0 0.82490540 ]
      /Gamma 2.2
]

in stead of /DeviceGray should work for converting sGray pages to pdf.

For AdobeRGB, you can use this:

[ /CalRGB
  << /WhitePoint [ 0.95045471 1.0 1.08905029 ]
     /Gamma [ 2.2 2.2 2.2 ]
endobj

For sRGB, though, you'll have to embed the icc file.

AFAICT, put the space in an object and specify a ref to that object
where you currently specify /DeviceRGB, usw.

-JimC
--
James Cloos <[email-masked]>         OpenPGP: 0x997A9F17ED7DAEA6
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