Re: BGRA, ARGB, etc. suggestion

In fact this could be done , but need something more than just 
additional chunk.
E.g. MNG use filter=64 for altering colourspace 
http://www.libpng.org/pub/mng/spec/#mng-IHDR

But this will break compatibility with all current readers. Maybe 
someday it will be good to do "PNG 2.0" as I mention before in 
discussion about FLIF (with new filters and compressions) and colour 
altering may be part of this.
However colour altering couldn't be extension for current PNG specification.


21.12.2015 2:17, Glenn Randers-Pehrson пишет:
> chNL would compete with Apple's CgBI chunk and perhaps violate their 
> "patent applied for".  Even though the proposed name is different, it 
> would serve the same purpose: making PNG files unreadable.
>
> Libpng supports BGRA and ARGB (reads RGBA pixels from a PNG file and 
> converts them on-the-fly to your desired format.
>
> Supporting 32-bit samples would not be trivial because the spec and 
> library would have to be redone to allow values greater than (2^31 - 
> 1) so I don't expect that proposal would be accepted.
>
> The PNG specification itself says that chunks like chNL and CgBI 
> violate the guidelines for new PNG chunk types:
>
> http://www.w3.org/TR/PNG/#B-NewChunksAppendix
>
> "Do not define new chunks that redefine the meaning of existing chunks 
> or change the interpretation of an existing standardized chunk, e.g., 
> do not add a new chunk to say that RGB and alpha values actually mean 
> CMYK."
>
> Glenn
>
> On Sun, Dec 20, 2015 at 3:16 PM, Alexey Solovey <[email protected] 
> <mailto:[email protected]>> wrote:
>
>     Hello. I suggest to make chNL chunk for declare how should works
>     png: in BGRA, ARGB, or another format. Also I suggest 32-bit
>     grayscale support.
>     Probably, I suggest maSK, that released in BMP format. Glenn?
>
>
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