questions about gamma correction and raw_image_visible

[davidenitti]

I would like to understand how to get the linear color value from the raw_image_visible from a RW2 file. the raw values seems to be 14 bits (I mean the values are below 2^14) and they do not seem similar to the postprocess image with gamma=1,1. for example raw values are never 0, while in the postprocessed there are 0 values. excluding demosaicing (I'm comparing a raw pixel with the relative color in the postprocessed image), why I see different values? is there any processing I'm forgetting? maybe white balance? but this does not explain the 0 values.

• is gamma=1,1 enough to get linear values even though postprocessing requires the colorspace? (which by default is srgb).
• is raw_image_visible already the linear value or requires something?
• it's hard to understand because I'm not sure whether matplotlib is always expecting gamma corrected images or not.

thanks!

[letmaik]

raw_image_visible is no different than raw_image, just cropped. Postprocessing always involves some rescaling, but the values you get when using gamma=(1,1), no_auto_bright=True, output_bps=16 should be as linear as it gets. If that doesn't work, please ask in the libraw forums.