Nikolay Pokhilchenko wrote:
There is no channel-different scaling by any factor in RAW data from camera. I hope it's possible to setup raw converter parameters to get true equivalence between *.tif and RAW data without white balancing, at least for "RGB" sensor cameras.
That may be possible if ICC profiles are not involved. But ICC models all assume PCS white point relative PCS values, so unless the white point of the chart happens to be exactly D50, white point adaptation is part of the device to PCS ICC model.
I think the non-linearity of "RGB" (most likely LMS) data from sensor must be compensated before matrix conversion to allow the next conversions to be truly additive nor multiplicative. At this step compensation may be equivalent for all channels. Can
This only makes sense for an XYZ PCS. An Lab PCS is not additive. It also confuses the dual effects of the device input curves. The shape of the device curves in optimising additivity is only effective within each CLUT cell. The actual location of the CLUT cell boundaries (the grid mapping) can be set independently of the shape of the curve within the cells, so the linearity goal actual has no influence over the overall device curve shape. [If you look closely at some typical Argyll CLUT device curves you will notice a subtle "scallop" shape which is a result of optimising the grid location independently of the per cell interpolation.]
it be implemented in standard ICC profile based workflow? May be it's exclusive feature of RAW converter? May the ICC profile based workflow do the input curves application before matrix conversion? If so, then the switch for equalisation of input curves may be justifiable.
It's hard to guess what typical raw tools workflow actually is. Some may attempt to do white balancing prior to ICC based color space conversion, although any such variables will tend to invalidate the profile. Personally I'd be looking at creating a workflow in which the ICC profile is used to convert the raw input into absolute XYZ space, and then apply rendering effects such as white balance etc. in XYZ space. For this purpose, a matrix profile may be a better bet than typical CLUT profiles, since CLUT profiles may not have the required accuracy over a raw images full dynamic range.
conversions, isn't it? Genuine raw output is unacceptable for direct viewing as standard RGB image, but I believe it's the best data source for color managed workflow.
Hmm. A lot of discussion about RAW gets carried away (IMHO) about the distinction between the raw bayer output and the RGB image. As far as I am concerned it's pretty meaningless to have a pixel with a certain filter over it, and then to forget this and treat it as a "non color" pixel. If a pixel has a particular filter over it, then it is labeled by the color of the filter right from the start.
IMHO, it will be better to disjoint geometrical conversion from subpixels to pixels in RAW converter and ICC-conversion in CM-software.
The labeling of pixels with their filter color and possible spatial interpolation is certainly of little interest as far as color is concerned. Graeme Gill.