Re: [Lcms-user] Apply profile with PCS = cmsSigXYZData, Color Space = cmsSigGrayData

[Aaron B. <bo...@gm...>]

Hi Marco,

Thanks a lot! Would you be able to take a quick look at my changes ?

Commit is here:

https://github.com/GrokImageCompression/grok/commit/8d62e2252fefd4a15124cac73c7f47a65fde651d

and complete file is here:

https://github.com/GrokImageCompression/grok/blob/master/src/bin/jp2/convertpng.cpp


Existing code already had some code for gamma curve, so perhaps I need to
disable that?

Cheers,
Aaron



On Tue, Feb 21, 2017 at 2:28 AM, Marco Freudenberger <
Mar...@en...> wrote:

> Aaron,
>
>
>
> I might be able to help a little.
>
>
>
> You need to write the iCCP chunk. Also make sure you have no conflicting
> entries in other chunks (sRGB, gAMA, cHRM chunk). PNG is a bit delicate in
> terms of possible ambiguous color space info in header.
>
> You also need to know, that some PNG readers don’t handle the color space
> chucks gracefully (specifically gAMA, cHRM – even Photoshop is clunky in
> that aspect, at least if no iCCP chunk is present).
>
>
>
> Do you use libpng ? If so, you need to do call
>
> png_set_iCCP()
>
> during your file creation to write the ICC profile.
>
>
>
> Marco
>
>
>
> *Von:* Noel Carboni [mailto:NCa...@Pr...]
> *Gesendet:* Montag, 20. Februar 2017 13:03
> *An:* 'Aaron Boxer'
> *Cc:* lcm...@li...
> *Betreff:* Re: [Lcms-user] Apply profile with PCS = cmsSigXYZData, Color
> Space = cmsSigGrayData
>
>
>
> >Noel, do you know where I could find sample code to read/write ICC
> profiles for PNG format?
>
> Sorry, I really don't, offhand.  I'd probably rely heavy on Google for
> that.
>
>
>
> -Noel
>
>
>