Question about Gamma correction

I had a question about Gamma correction applied by libraw during the call to dcraw_process. I came across this post but I have a couple of follow-up questions.

1. The libraw documentation says by default gamm[] has values for the BT.709 workspace. Does this mean that I need to update this value if I request data in the sRGB or Adobe colorspaces? What gamm should I use for the Wide Gamut colorspaces?

2. Is the gamma correction applied when I request data in the camera space OR do I need to explicitly gamm[0] and gamm[1] to 1 to obtain linear output?

I looked at convert_to_rgb() and it does not appear to update the gamm depending on the output colorspace.



gamma curve is applied on

gamma curve is applied on final output stage (tiff/ppm writer, or make_mem_image)

If you're working with imgdata.image[] directly: these values are linear.

-- Alex Tutubalin @LibRaw LLC


I am working primarily using raw_image, image3[], image4[] and those are linear.

I am using dcraw_process as a reference and wanted to confirm what specific gamma is applied.

My guess would be that I need to set gamm correctly depending on my output colorspace. Applying BT.709 gamma when requesting a sRGB output probably returns subtly incorrect results.


Neither gamma, nor colour

Neither gamma, nor colour space chromaticities are relevant in a colour-managed workflow. For non-colourmanaged workflow (publishing to internet, for example), use sRGB D65 with simplified gamma 2.2, like Adobe are doing it. In any case, make sure the resulting profile is embedded into the output.

Iliah Borg