Vadim Plessky ([EMAIL PROTECTED]): > On Monday 15 July 2002 10:12 pm, Owen Taylor wrote:
> > > > If you do a web search you should be able to find some gamma > > > > test patterns; you can then play around with 'xgamma' until you > > > > have a gamma of 2.2 and see if the screenshots look better. > > Can you pls provide URL for the patterns which are the best, according > to your taste? And what do you mean under "screenshots look better"? > I think it's very subjective - wether screenshot looks better or not. > Any way *to measure* and return back some alpha-numeric value, > indicating wether gamma is o.k. or not? You can measure the gamma of your device using a photometer or similar device. Unfortunately, the cost might not be justified in your case. That leaves you to perform empirical measurements. Here's one I just found: http://www.graphics.cornell.edu/~westin/gamma/gamma.html However, that only shows test patterns generated from a simple first order approximation. It does describe some of the problems in testing gamma. One of the problems I've found is that a CRT at high resolutions usually does not have a fine enough grid to resolve individual pixels correctly, causing strange blurring effects. I recommend testing CRTs at a low resolution, say 800x600 or 1024x768, for best accuracy. > > Something like: > > > > xgamma -gamma 1.2 > > I tried it with my system, I see changes on screen. So I guess my ATI > Rage Mobility+LCD is supported. Not sure, though, what should be > final result. It's probably best to calibrate your monitor for the sRGB standard: http://www.srgb.com/ This means you should correct your monitor such that it mimics the sRGB gamma of 2.2. Your digital photos, DVDs, and other pictures will then (theoretically) look more correct. To do this, you first find an approximation to your gamma curve by finding one of these test patterns, measurement, or what not. Say your display device is best approximated by a curve with an exponent of 2.6. You then find the correction to get from 2.6 back to 2.2. In this case, the correction is 2.2/2.6 == 0.84615. Run 'xgamma -gamma 0.84615' and all is well. > > will adjust it ('man xgamma' for details), assuming your video > > driver supports it. Not all do, even when the hardware has the > > support. > > man:xgamma is not very informative. It lists options, but even > doesn't tell you what is the valid range for the gamma!... And no > explanation, how someone should change his gamma. This is quite true. I've been meaning to write a new man page myself for it, since clearly none of the x developers are rushing to do it themselves. As well though, the curves installed by xgamma I think could be much improved by adhering more closely to the sRGB standard. -- Billy Biggs [EMAIL PROTECTED] _______________________________________________ Render mailing list [EMAIL PROTECTED] http://XFree86.Org/mailman/listinfo/render
