Hi Mike, That's very interesting. So what you're basically saying that blending will give different results in different spaces including PCS's.
For some reason I assumed the PCS's are general enough to do all blending properly, but that could be due to some conceptual misunderstanding of color spaces, profile and/or blending. So if I understand correctly, to get accurate results, I MUST blend in the profile/color-space of the canvas, right? As for writing code to blend CMYK, it is simple. However, I use openGL since I render real 3D data, and I need other features openGL has to offer like depth-testing. So I really don't have a choice here. Yaron > > You're making sense. Blending in Lab or XYZ space might give a reasonable > preview but the appearance will differ significantly from a 4 channel CMYK > alpha blend. > > RGB, being a close cousin of CMYK, would probably be a better space for an > approximate blend than either Lab or XYZ. For example, CMYK(100,0,0,0) > and CMYK(0, 100, 0, 0) with a 50% alpha will blend to CMYK(50, 50, 0, 0). > In Lab space (using Photoshop with the v2 SWOP coated profile for the > numbers) the corresponsing colors in would be Lab(62, -44, -50) and > Lab(52, 81, -7). Blending these in Lab space gives Lab(57, 59, -28), or > CMYK(21,77,0,0), a significantly brighter and warmer color. A similar > problem will happen in XYZ space. > > I also doubt that doing the extra conversion into and out of the PCS will > be at all efficient. Although RGB might work, there may be a similar > efficiency issue, depending on how accurately you want the conversion to > be. One solution that would be fast and accurate would be to write your > own CMYK alpha blending code to handle four channels + alpha directly. > This is not a difficult piece of code to write, and a simple loop that > does an alpha weighted average of the four channels will be faster than > any set of color conversions. > > Mike Russell ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user
