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<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">Ira,<div><br></div><div>The gamma value 2.2 is an approximation for sRGB, and since sGray has never been formally defined we went with "just like sRGB just grayscale". The following plot shows a gamma 2.2 line (dotted blank line) against the sRGB curve (solid red line). You'll notice that the values are almost exactly the same.</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span><a href="http://en.wikipedia.org/wiki/File:SRGB_gamma.svg">http://en.wikipedia.org/wiki/File:SRGB_gamma.svg</a></div><div><br></div><div>A search for any specifications on sGray turns up nothing, and all of the other "hits" on the term points to sGray using the same transfer curve as sRGB.</div><div><br></div><div>So I'd be interested in seeing what reference James is referring to, because *I* haven't seen it and the CUPS raster definition goes back quite a few years...</div><div><br></div><div><br></div><div><div><div>On May 31, 2014, at 10:46 AM, Ira McDonald <<a href="mailto:blueroofmusic@gmail.com">blueroofmusic@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div dir="ltr"><div><div><div><div><div>Hi Mike,<br><br></div>From Open Printing mailing list - apparent discrepancy in <br></div>PWG Raster spec definition for "sGray".<br><br></div>Please take a look at this.<br>
<br></div>Cheers,<br></div>- Ira<br><div><div><div dir="ltr"><div style="display:inline"></div><div style="display:inline"></div><div style="display:inline"></div><div></div><div></div><div></div>
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<br><br><div class="gmail_quote">---------- Forwarded message ----------<br>From: <b class="gmail_sendername">James Cloos</b> <span dir="ltr"><<a href="mailto:cloos@jhcloos.com">cloos@jhcloos.com</a>></span><br>Date: Sat, May 31, 2014 at 5:30 AM<br>
Subject: [Printing-architecture] pwgtoraster vs calibrated spaces<br>To: <a href="mailto:printing-architecture@lists.linux-foundation.org">printing-architecture@lists.linux-foundation.org</a><br><br><br>I was wrong about sGray. It turns out that sGray is not defined as<br>
having the same curve as sRGB, but rather it always has gamma 2.2.<br>
<br>
The cupsraster document says srgb gamma/whitepoint, and the pwg raster<br>
doc says srgb grayscale. But everything else I've found says 2.2.<br>
And it seems a D50 illuminate.<br>
<br>
That being said, this colorspace dictionary:<br>
<br>
[ /CalGray<br>
<< /WhitePoint [ 0.96420288 1.0 0.82490540 ]<br>
/Gamma 2.2<br>
>><br>
]<br>
<br>
in stead of /DeviceGray should work for converting sGray pages to pdf.<br>
<br>
For AdobeRGB, you can use this:<br>
<br>
[ /CalRGB<br>
<< /WhitePoint [ 0.95045471 1.0 1.08905029 ]<br>
/Gamma [ 2.2 2.2 2.2 ]<br>
>><br>
endobj<br>
<br>
For sRGB, though, you'll have to embed the icc file.<br>
<br>
AFAICT, put the space in an object and specify a ref to that object<br>
where you currently specify /DeviceRGB, usw.<br>
<br>
-JimC<br>
--<br>
James Cloos <<a href="mailto:cloos@jhcloos.com">cloos@jhcloos.com</a>> OpenPGP: 0x997A9F17ED7DAEA6<br>
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<span class="Apple-style-span" style="border-collapse: separate; font-family: 'Andale Mono'; border-spacing: 0px;"><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: 'Andale Mono'; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">_________________________________________________________<br>Michael Sweet, Senior Printing System Engineer, PWG Chair</div></span></span>
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