Re: CFD: zXIF 2017-0207

On 10 February 2017 at 23:07, John Bowler
<[email protected]> wrote:
> [...] There is a whole lot of stuff
> in CIPA-2016 which is related to the encoding of the image
> information. [...]

This is both true and irrelevant to the intended rendering.

In PNG, gAMA/cHRM/sRGB/iCCP are all about the intended rendering.
There is no conflict whatsoever between the proposed eXIf and
gAMA/cHRM/sRGB/iCCP.

> I can't remember a profile.

Ok. *If* the color profile does exist, (and in my workflow,
admittedly, heavily based on Raw processing, it often does), that is
actually relevant to the intended rendering, and that's what would go
into PNG-sRGB or PNG-iCCP. In addition to (and completely orthogonal
to) what would go into PNG-eXIf.

> But, ultimately, you miss the point; the EXIF data from at least some
> cameras contains information that allows the original information to
> be reconstructed.  This is contained in the original white point and
> the original luminance levels - the absolute light levels.  With that
> information it is possible to combine two images from different
> sources in a meaningful way semi-automatically, without it the result
> just looks weird.

In EXIF, the info you're mentioning is about camera manufacturing,
camera settings at capture time (not render time), and overall
usability. Specifically, it's the information meant for communicating
between camera hardware, firmware, software, and, ultimately, the user
(i.e. the photographer).

Concepts like sRGB or YCbCr are not applicable to the Raw image
format. (Let us even forget PNG, for a moment.) So how do you explain
the presence of these EXIF fields in the Raw image file, for example?
Or, here is another question: why is the Raw image said to be
"natural", or "vivid", or "muted", or even "monochrome" (if that's
what the user chose in the camera settings)? The Raw image coming out
of a conventional camera is always in color, never monochrome; so what
is that particular EXIF field even supposed to mean?

It's because this is what the photographer is shown e.g. when toggling
the Info button on the camera. These are the colors used in the Raw's
thumbnail, too. So if I captured a photo in Raw+JPEG format, muted
mode under the sRGB profile, it tells me that on the LCD display. If I
captured it in vivid mode under the AdobeRGB profile (not JPEG, just
Raw, because the few cameras that do capture AdobeRGB, AFAIK, only
capture it in Raw), with a custom user adjustment of noise reduction
by minus one, and an exposure compensation of +1/3, etc., it tells me
that, too.

Moreover, this is what the photographer gets when importing, say, the
Raw image into the photo processing software on a computer. There are
many knobs adjusting colors (incl. colorspace), sharpness, scene mode,
noise reduction, etc. etc. etc. The Raw image contains all the
information at the time of capture, and sets the adjustments knobs to
their default positions in the software -- defaults that are meant to
match the original settings and knobs from the physical camera.

It is the EXIF data that communicates all this information, from the
on-camera user settings to the post-capture processing software. It
works regardless whether you load a Raw image, or a JPEG, or a TIFF.
The processing algorithms are different, of course, but the adjustment
knobs in the user interface are set in the same positions, and work in
the same ways.

Now, you may drag the sharpness slider all the way to "soft" or all
the way to "sharp". You may drag the color slider all the way to
"monochrome" or all the way to "saturated". The original screen
capture information is still there, regardless, and the fact that you
changed it does not invalidate how it was set originally; or how it is
recorded in EXIF; or how it was used in Raw conversion (be it during
or after taking the photograph).

Some of the Raw processing software that I use leave the EXIF info
almost entirely unchanged, or changed in inconsequential ways,
regardless what adjustments I make in Raw, and what JPEG or TIFF
output I get out of it. Others do change it. I use many photography
software programs, and I don't actually keep track.

In conclusion, I see no good reason to impose in the PNG proposal a
behavior that is any different from how it currently works with the
already-existing formats.

Sincerely,
Cosmin

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