sRGB colorspace and ProPhoto RGB ICC Profile - Which is it?

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marcel24
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sRGB colorspace and ProPhoto RGB ICC Profile - Which is it?

Post by marcel24 » 2019-03-15T07:58:47-07:00

Image

Example 11 and 12. How is it possible that the color space is sRGB and the profile is ProPhoto RGB?

Which one is actually used?

snibgo
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Re: sRGB colorspace and ProPhoto RGB ICC Profile - Which is it?

Post by snibgo » 2019-03-15T08:12:22-07:00

The %[colorspace] format comes from image metadata that IM creates. This can take values such as sRGB, RGB, Lab, CMYK, HSL and so on. Logically, when there is a profile, this metadata should record that the channels are red/blue/green or whatever, but the actual colorspace (the primaries etc) are defined by the profile.

And that is really what %[colorspace]=sRGB when there is a profile really means.

Most operations in IM (blur, composite etc) are independent of the colorspace -- they are mathematical operations on pixel values, and IM doesn't need to know what colours are represented by those values.
snibgo's IM pages: im.snibgo.com

marcel24
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Re: sRGB colorspace and ProPhoto RGB ICC Profile - Which is it?

Post by marcel24 » 2019-03-15T08:46:31-07:00

So your saying if there's a profile present the colorspace will be ignored?

snibgo
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Re: sRGB colorspace and ProPhoto RGB ICC Profile - Which is it?

Post by snibgo » 2019-03-15T08:58:00-07:00

Ignored by what?

As I say, most IM operations ignore any profile, and don't care what the %[colorspace] is. A small number of operations will change the %[colorspace] to sRGB if it isn't already.

IM will copy a profile from input to output. So if you composite a ProPhoto image over an sRGB image, the result will have the profile from the first input, but the result will be wrong -- you should first convert (with "-profile) one image to the same colorspace as the other.
snibgo's IM pages: im.snibgo.com

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