[argyllcms] Re: Strange results on a projector

Frédéric wrote:


But we got very bad results (not argyll fault!). After the LUT is loaded,
there is no color cast in grey scale, but when looking at slideshows,
there are very bad colors: images often have a green color cast,
especially human skin tones, which looks hugly.

Do you know why we obtain such bad results? Could it be a mixing color
problem from the projector? I mean near grey colors, all is fine, but
other colors are not OK. Is it a know issue with LCD projectors? Is
there a way to correct this with argyll, without color space conversion?


I've not personally seen this, but then I haven't done much projector
calibration/profiling. Are you sure it's an LCD, and not (say) a 4 color
segment (R,G,B and White) DLP ?

If a device is actually additive, then unless the primaries are in
very strange locations, it should behave itself reasonably once the
per channel curves have been adjusted to give a neutral. The main
mechanism for non-additive behaviour in a modern projector
would be that something electronic is manipulating it.
A 4 segment DLP has such manipulations, or maybe some projectors
have various "enhancement" modes that mess with things, and make
the basic RGB behaviour non-additive.

If the behaviour is dynamic (as some enhancement modes are),
then color management is basically useless. If it static, then
the classic answer using color management is to characterize
the device, and then color correct the slides. For non-additive
behaviour a LUT based profile would be needed.

If this isn't an option open to you (and it does take some
messing around), does the projector have a mode that is
better behaved ? I understand (for instance) that many 4 color
segment DLP's have a 3 segment (RGB) mode, that is not as bright
but gives a bigger gamut and would probably behave better from
a color management point of view. If it's some other type of
projector, them maybe it also has a better behaved mode.

Do you know what the make and model are ?

Graeme Gill.

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