PNG with embedded sRGB

[bjon]

Hi

I want to embedd a srgb profile to a png image. Doing that on a jpg everything works fine (i got a "Profiles" section when running identify on output image)
When doing the same thing on a png image everything seems to work (no errors) but "Profiles" section is missing when using identify.

Im i doing something wrong here? Or is this expected?

[snibgo]

The docs say (somewhere; I forget where) that if IM is writing a PNG with sRGB profile, it just sets a PNG flag that says it is sRGB.

[bjon]

Im my case the input png does not have a srgb profile (but got colorspace=sRGB)

[snibgo]

I don't understand. The input has no profile, and you are not adding one, but expect the output to contain a profile?

Can you provide the exact command you are using, and the input file?

[glennrp]

The docs say (somewhere; I forget where) that if IM is writing a PNG with sRGB profile, it just sets a PNG flag that says it is sRGB.

That's correct. The PNG spec defines the "sRGB" chunk that carries only one byte: the "intent". We write that instead of the full sRGB profile. Any application
that understands ICC profiles is supposed to also recognize the PNG sRGB chunk and handle it as though a full sRGB profile were present.

[bjon]

I don't understand. The input has no profile, and you are not adding one, but expect the output to contain a profile?

Can you provide the exact command you are using, and the input file?

Code: Select all

convert input.png -profile srgb.icc output.png

[bjon]

The docs say (somewhere; I forget where) that if IM is writing a PNG with sRGB profile, it just sets a PNG flag that says it is sRGB.

That's correct. The PNG spec defines the "sRGB" chunk that carries only one byte: the "intent". We write that instead of the full sRGB profile. Any application
that understands ICC profiles is supposed to also recognize the PNG sRGB chunk and handle it as though a full sRGB profile were present.

Aha now i got it
Thanks for the clarification!

[snibgo]

Just to add to the explanation:

If input.png has a profile, your command will convert the pixel values and add the profile. Otherwise, it will just add the profile. Then, because you are saving sRGB as PNG, it will save the sRGB chunk rather than inserting the actual profile in the file.