[argyllcms] Re: Display Calibration. Setting up RGBCMY Hue/Saturation controls.
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 18 Mar 2011 10:57:19 +1100
Ivan Kadomin wrote:
I'm trying to calibrate and profile my display. In it's OSD panel there
are some presets "Standard", "sRGB", "AdobeRGB", etc. and also "Custom
Colors".
Hmm. It seems to be missing an important setting, something that
would be called "Native" !
In all modes except the "Custom Colors" Contrast and Brightness
settings are available only. In "Custom Colors" in addition to RGB Gain
and RGB Bias controls there are RGBCMY Hue/Saturation controls.
In dispcal utility there are options that help user to properly setup
RGB Gain and RGB Bias. But how should I act to setup RGBCMY
Hue/Saturation controls of the display properly?
Basically the RGBCMY controls are applying an interpolation to map
the incoming RGB to the native RGB. So if you are not trying to
emulate some other color space in hardware (like sRGB or AdobeRGB),
then you should be trying to set the RGBCMY controls to maximum
gamut. Now if these controls have been done well, you won't
be able to set them beyond the native gamut of the display. If
they've been done badly, they will let you set values beyond the native
gamut, and there will be clipping, which would be bad.
One idea for figuring out what's going on would be to setup
dispwin -n -m and spotread -e, and adjust each color for maximum
chrominance - a^2 + b^2 (Sorry about that, I'll add an LCh display
mode to spotread to make such things easier). If you get to a point
where you increase the controls and nothing changes, you know
it's clipping. If the controls are in xy coordinates, then you
could try spotread -e -x, which will show Yxy. A shortcut would
be to figure out the best (most saturated) RGB values, then
compute the straight line xy values between these for the CMY
values, since this will be the case for an additive device.
The advice for Hue/Saturation is similar. You would need to
discover what the "do nothing" or "native" settings are.
[The manufacturer sure aren't making this easy!]
Graeme Gill.
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