El 28/07/16 a les 11:20, Roman Lebedev ha escrit: >> I need the AMD closed source graphics driver because, as far as I know, >> the open source radeon driver does not allow using the 12 bit LUT >> present on AMD cards. And this is needed to acurately profile a monitor >> (using ArgyllCMS or DispcalGUI), without banding artifacts. > > Hm, where did you read that? > Also, if it really is the case, is this issue already reported against > open source radeon driver? > > (and, does argyll actually produce > 8bit vcgt? because if it does not, > the issue is bogus) > > TBN i don't really believe there is any banding even with 8-bit bit depth.. >
I did not read it, I have seen it myself. Using the "dispcal" command from ArgyllCMS with these params: dispcal -y l -R the programs shows the value for the apparent videoLUT's bit depth. With an Intel integrated graphics, or a Nvidia Geforce gamer card, or an AMD using the opensource radeon driver, the value shown is 8 bit. But with an AMD card using the Catalyst binary driver for Linux, the returned value is 10 bit. Old ATI cards have 10 bit LUTs, current AMD cards have 12 bit LUTs. The test used by dispcal only detects the difference between ordinary 8 bit LUTs, and LUTs with higher bitdepths. So a returned value > 8 bit means that the AMD 12 bit LUT is working. And, yes, profiling the monitor with Argyll and the Catalyst driver takes advantage of this, I have evidence of it. Profiling with and ordinary 8 bit LUT does not show much banding i an sRGB monitor with a good "from factory" response, with good neutral grays, and a white point defined in OSD that does not differ too much from the target white point you chose in Argyll, and also the gamma setting needs to be the same. But with widegamut monitors, or monitors with a less than ideal response, o when you can't adjust the desired white point or the gamma on the OSD ... a 8 bit LUT shows banding that a 12 bit LUT does not show. And when you validate the profile with DispcalGUI you can see how many of the originally available 256 levels per channel get lost using a 8 bit LUT. I use a Dell UP2516D (wide gamut). And, even being a hardware calibrated monitor, I need my AMD card with 12 bit LUT to get the final icc profile, because Dell's internal calibration and also precalibrated modes have several flaws. These "cheap" wide gamut monitors suffer badly from lack of uniformity. You can get rid of it enabling "Uniformity compensation" in Dell's OSD, but this value has no effect in custom callibrated modes (CAL1 and CAL2), only in a generic wide gamut "Custom color mode", (quite similar to the ECI RGB v.2 colorspace) but the uniformity compensation disables the individual color channels gain controls ... so I can't chose the white point in OSD, so I need to let it in native value and set te desired white point as a target in DispalGUI when profiling ... I could'nt do that with good enough results with a 8 bit only VideoLUT. I have learned all this stuff thanks to the expertise of a contributor in a spanish Canon's users forum, "Canonistas.com". His nickname is "ColorConsultant". He has written a series of FAQ's about monitor profiling, and buyers recommendations on monitors for photography, and callibrating devices, that are worth reading, if you know a little of spanish: http://www.canonistas.com/foros/blogs/colorconsultant Josep V. Moragues ___________________________________________________________________________ darktable developer mailing list to unsubscribe send a mail to darktable-dev+unsubscr...@lists.darktable.org
