Alan Corey <alan01...@gmail.com> writes: > I did a little playing with dcraw to tiff and ppm and I was shocked at > how different they are from the jpegs. I would think shooting color > ramps, measuring, and fitting the results to curves might be close to > what you're talking about.
Keep in mind that different != wrong, in some ways. There is scene luminance, which raw should arguably be trying to record, and then there is developed digital file luminance, and then there is print luminance. Photography has a long history of transforming scene luminance (via negative density) to print luminance in a pleasing transformation vs a quantitatively accurate one. The Ansel Adams writings about the zone system and -/+ development is interesting. However, all that said, when you have a reasonable illuminant, and spot meter on a grey card, then you expect to get something that's mid-range in the camera-produced jpeg and also in the jpeg/tiff/whatever produced by raw conversion with +0 exposure compensation. And also the white card should be two stops higher (90 vs 18). If I had more Copious Spare Time, I'd focus on just that first. In my experience that's most of the issue. > This is something I was working on for printer calibration before I > gave up and bought a Color Munki. I'm not sure I finished a parser > for reading back the printed out versions from a scan. Linearity and > the range of actual colors would be an issue. I think I was looking > at the mixing that happens here because printers use cmyk and I was > trying to look at rgb, so whenever I'd ramp up one color others would > go along with it. Some of that might have been to create a value > change. There are multiple open source projects for calibration/profiling. lprof seems inactive but worth looking at, and Argyll. lcms2 can do cmyk/rgb converesions, I think. I have also seen IT8 targets available, plus color checkers are not that expensive.
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