If I understand the spec correctly, it says (pretty much like I thought), that all objects should be converted to the output device's color space and composited there (unless I misunderstood).
In my application, even if I use one input profile, if it's CMYK I still have a problem, since I'd need the 2 rendering passes. Actually, the cause for the problem is that the canvas/document can have a CMYK space (that's equivalent to rendering the PDF to a CMYK output device). Is it possible to convert CMYK to CMY and back without losing accuracy or gamut? If so, I could use CMY to render in openGL, and then convert back to CMYK. > -----Original Message----- > From: Kai-Uwe Behrmann [mailto:[EMAIL PROTECTED] > Sent: Tuesday, December 05, 2006 2:48 PM > To: Yaron Tadmor > Cc: Lcms Liste > Subject: Re: [Lcms-user] alpha blending in LAB space > > Possibly reducing the number of blending colour spaces is a solution. > Blending of mixed colour space layers is not a consistent thing anyway. > > You could read the pdf spec how it was solved there. Chapter 7.2.3 > in the pdf reference 1.6 for instance. > > regards > Kai-Uwe Behrmann > + development for color management > + imaging / panoramas > + email: [EMAIL PROTECTED] > + http://www.behrmann.name > > > Am 05.12.06, 14:18 +0200 schrieb Yaron Tadmor: > > > Hi Kai, > > > > First, Thanx for the help. > > > > > > I'll try to explain better what I do. > > I have several layers 1 to n, each with its own profile (let's call it > > profile-i). I'm blending them all together (similar to layers in > > PhotoShop) on a single canvas which has its own profile as well (let's > > call it profile-c). I use profile-c as the output profile for exported > > images from my software (the output of the application). Now we also > > have the screen profile I'm showing the user the data on (let's call it > > profile-s). > > > > What I first did was this: For display, I convert all layers to > > profile-s, so I have n conversions profile-0->profile-s to > > profile-n->profile-s. Then I blend layers in profile-s. For output I do > > the same with the destination profile being profile-c. The problem here > > is that the blending output is different. > > That is, the result of the blending depends on the profile I'm blending > > in. > > > > I figured out the proper thing to do, is to always convert layers to > > profile-c, blend, and then if I'm displaying convert the result to > > profile-s for display. > > > > I hope up to here everything is clear. > > > > For this, blending can be done with openGL even if the format is 8-bit. > > The problem is that if profile-c is CMYK, I need to do 2 passes with > > openGL, since openGL doesn't support 4 color channels. So that's the > > problem. > > > > I thought of blending in LAB PCS to avoid blending in CMYK and doing 2 > > passes. However my concern was exactly the one you pointed out. That LAB > > is a wide space, and I might lose precision and get color stepping. So I > > guess my worries were justified. :-) and :-(. > > > > So I guess my question, is if there's another thing to do what I want to > > do? I'm using openGL since I use 3D graphics to create the layers. They > > can be turned and manipulated in 3D space. openGL gives me a robust and > > easy to use rendering engine which also does depth testing on hardware. > > > > I don't think openGL poses any performance problems or bottlenecks. As > > long as I really give the GPU RGB (or CMYK) data, it does everything > > fast and accurate. Perhaps giving it LAB data would be asking to much of > > low-precision GPU's, and that's exactly my question. > > > > Yaron > > ------------------------------------------------------------------------- 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
