Photoshop's use of monitor profile
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From: Bill Hilton on 19 Jun 2005 17:04 >Paul N writes ... > >Which means that non color managed apps show 'partly corrected' images. >A good thing in itself. But what part?? 90%? 50%? Unpredictable? Think about it like this ... your monitor is probably set up to deliver 9300 Kelvin color temp with all 3 color guns at or near full strength. You are probably set up for say 6500K instead, which means you have to back off the blue and green guns a bit when you set the custom white point with the Sypder software. For example, on a monitor I just checked for 6500K R=100, G=85, B=80 ... this gives you the correct white point for this monitor (and I think this is the info that gets loaded into the LUT when the loader runs at start-up, though I'm not sure of that). This is for white ... as you display other colors you drive the guns with less strength (lower voltage) but they are not linear now, ie, red is on a 0-100 scale, blue 0-80 scale etc, plus any other non-linearities built in due to changes in phosophors, etc over time. So part of what the ICC profile does is correct for the non-linearities (probably not the right word but you get the drift). In other words, once you've set the white and black points with the calibration then in an ideal world with perfect 'linearity' on all three guns and phosphors you wouldn't see much if any difference between colors displayed in a color managed app vs a non-color managed app, but in the real world the differences are measured by the puck and (hopefully) compensated for with the monitor's ICC profile. So to your question "But what part?? 90%? 50%? Unpredictable?" I would say it depends on how much your particular monitor varies from linear (and the accuracy of your profile). You can check the variation with a test target like this one http://members.aol.com/bhilton665/colors.jpg (feel free to download it or make your own) ... toggling 'monitor profile' (ie, ignore the ICC profile) on/off (ctrl-y) on my monitor shows that the bottom 3 rows are largely unchanged and the top two rows with saturated colors change mostly in the reds, yellows and oranges, with blues and greens less affected. Your monitor may show something different, but at least you'll know which colors are most susceptible to color shifts as you move between apps. >You may argue that one shouldn't use non color managed apps in a >color managed workflow. I would just say that you shouldn't make color edits in a non-color managed app if you have a good color managed app like Photoshop, regardless of what else you use the non-color managed programs for. You should expect surprises in the colors that show changes in a pattern like the one I linked to. Bill
From: Johan W. Elzenga on 19 Jun 2005 17:10 Paul N <paul2n.replace-2-by-1(a)hotmail.com> wrote: > You may argue that one shouldn't use non color managed apps in a color > managed workflow. But for many amateur photographers like me, there are lots > of useful apps out there that are not color managed. So we have to live with > 'partially corrected' color; knowing what 'partially' means would IMHO be a > big help. You'd need to have a program that can graphically display color profiles. Then you can compare the color space (i.e. the profile) of your monitor to sRGB color space. The difference between the two is the difference you'll get with non-color managed applications. -- Johan W. Elzenga johan<<at>>johanfoto.nl Editor / Photographer http://www.johanfoto.nl/
From: Mike Russell on 19 Jun 2005 22:42 "Paul N" <paul2n.replace-2-by-1(a)hotmail.com> wrote in message news:3Ljte.285914 > > Actually the 'register level' is not my concern. What *does* concern me is > that -apparently- part of the color correction for display is done in > hardware and part in software. The "other part is indeed software dependent, and it consists of recognizing an image's embedded profile, and using that profile, together with the display profile, to display the image colors correctly. If an application honors embedded profiles, it is called "color aware". For example, a web browser could recognize an embedded profile in a downloaded jpeg, and display those colors correctly. If this were done universally, the old phenomenon of PC images looking darker on a Mac - or Mac images looking to light on a PC - would be solved. The vast majority of browsers don't do this, and for very good reasons that might be an interesting topic for another thread. -- Mike Russell www.curvemeister.com
From: yesnno on 20 Jun 2005 07:20 Bill Hilton wrote: > > >The OS and the video card must play some role in using a monitor's > >ICC profiles. What are they? > > The OS has to support ICC profiles and the ICC workflow or it can't > happen ... earlier versions of Windows didn't offer ICC support for > example, which was a real plus for Apple in the digital market. I > *think* Windows 95 offered ICM 1.0 support and maybe with 98 they came > out with ICM 2.0 support, which was not too far behind what Apple is > doing. In typical Windows fashion they declared this 'good enough' and > haven't improved it much if any since. I remember that an OS like NT > didn't support this because you couldn't write to the video card (or > something like that), for example. > > In Photoshop you can choose to use either the Adobe(ACE) conversion > engine or the Windows ICM option, which you can access in the Color > Settings (advanced - Conversion options) window. There was a time many would recommend using a Mac over a PC for "serious" graphics work. Are those days all but gone? On a Mac with Intel chips (soon), will the user see any difference in how colors are handled? > As for the video card, you would have to use a very old or very cheap > one with few programmable registers to miss out on the ICC stuff. Any > decent newer card should be fine. > > >Is choosing a video card important for color management and using > >ICC profiles? > > I don't think so (I'm no expert on video cards though), so long as it's > fairly recent. > > >using the same profile, will the displays look the same on the same monitor > >for different (but comparable quality) video cards? > > You wouldn't use the same profile for different video cards but if you > generate one specific for that card then I'd expect the monitor to look > the same. I should have stated that on the same monitor after switch a video card and generating a new profile, will the displays look the same. I think your answer is yes. > A good source of info on color management is "Real World Color > Management" by Fraser, Murphy and Bunting. > > Bill
From: yesnno on 20 Jun 2005 07:55
Bill Hilton wrote: > > >Paul N writes ... > >Many questions and no clear image of how all these pieces of the puzzle > >fit together. > > I wouldn't worry too much about what's going on at the register level > of the video card ... what's important is understanding that color > managed apps 'translate' colors between different devices. I agree completely. Given the choice, most of us would prefer spending our time shooting and printing over looking under the hood. But color management at this stage is neither push button simple, nor is the ROI from a set of good hw/sw in line with that from a good DSLR or a good monitor. After a > while you find that there are a lot of inaccurate ICC profiles out > there (especially printer profiles) and what's important is generating > or finding good, accurate profiles and knowing when you have a bad one. How true. The sad part is that many vendors can charge for bad profiles and get away with it. Profile vendors will talk about their equipment, etc. but will not educate their customers on how to evaluate their profiles and why theirs are better. Even the good vendors won't do it, leading me to believe that evaluating profiles is not as simple as it sounds. The customer can evaluate a profile by looking at the prints, AFTER spending the money. If he finds the prints unsatisfactory, there is no way for him to challenge the vendor. What we need is an education and tools on how to evaluate profiles, followed by a ranking of the profile vendors. You won't happen to know of a good profile vendor, would you? |