Vallo Kallaste wrote:
I have never used the dispcal -a switch before and would like to know when is it appropriate to use it? It certainly does something and the results are not what I would call pleasant. Thus I'd like to know if anybody is actually using it, when and why. Also, is it right to assume that usage is constrained to sRGB, REC 709 and SMPTE 240M only? I.e. the usage is not appropriate when calibrating to, say L* TRC?
If used at al, it needs to be used with some understanding of what's going on in a wider sense. It makes use of a color appearance transformation, which tries to preserve the appearance between different viewing conditions. Exactly like using device profiles, there needs to be some concept of source and destination viewing conditions to be able to create a transform. To simplify things, dispcal hides the source viewing conditions, and instead makes some assumptions based on the target curve selected. The assumption for REC 709 for instance, is that the source is captured in a high brightness studio situation, while your display may well be much dimmer, in a dim surround, therefore calling for extra contrast (ie. effectively a higher gamma). If the assumptions are incorrect, then the results will not be reasonable. In a real color managed situation, this will not be very relevant, since a display profile takes into account the display calibration (effectively nullifying it), and appearance preservation over viewing conditions is obtained in creating perceptual gamut mappings. Graeme Gill