Re: [libpng:feature-requests] #32 Modern compressor

On Fri, Dec 30, 2016 at 7:24 PM, Cosmin Truta <[email protected]> wrote:

> I would be happy enough to see our present-day PNG format being used
> in digital photography. Never mind exceeding 24-bit. Even for plain
> true-color images, deflate-compressed TIFF is more suitable than PNG,
> because TIFF can hold EXIF and PNG can't. For digital photographers
> (myself included), EXIF is super-precious.
>

I don't count myself as an originator, but as a user I agree very much; to
put it another way, EXIF is, de facto, a standard and as such any lossless
format must support it.

>
> In theory, PNG can hold any metadata. In practice, there have been two
> or three attempts by our group to incorporate EXIF into PNG, back in
> early 2000's, all of which failed.
>
> PNG can do XMP, instead of EXIF, and yet EXIF is the accepted industry
> standard (although Adobe may beg to differ). XMP did not catch on with
> any of the digital camera manufacturers that I know.
>

Ok.  In JPEG it's a binary blob contained in an APP marker.  There's lots
of code out there to decode the blob simply because, while it is binary,
the format is always well defined.

It's nominally safe-to-copy; there is some information in there (such as
the modification date) which some might argue isn't, but that is really
moot because 'modification' in the Exif context means a real change to the
image, not the kind of encoding change that things like pngcrush or OptiPNG
do.

So it's eXIf; just a blob, forget the compression complexity.  Unofficially
it would be exIf with, just, the blob as the data.

John Bowler

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