Ive <ive### [at] lilysoftorg> wrote:
> Am 4/2/2021 um 4:23 schrieb Kenneth:
>
> Just to make it clear - as I have the impression you do misunderstand
> the srgb keyword: it is NOT about rgb-to-srgb conversion, it is the
> other way around. The srgb keyword is for converting a given sRGB color
> value to a linear RGB color.
>
> > Long ago, either you or Clipka had given a different kind of example of this,
> > but used an rgb value of something like
> >             rgb <104,230,75>/255
> > and then warned about naively converting that to srgb with a simple
> >            srgb <104,230,75>/255
> >
>
> ...Quite the opposite: this is exactly what the srgb keyword was
> meant for. You have a byte values (either from a color picker or from
> some web color), and the division by 255 transforms this byte value into
> the 0..1 range. The result is still a sRGB value and prefixing this with
> the srgb keyword simply tells POV-Ray to treat it as such and internally
> converts it to a linear RGB value.
>

This description of the 'srgb' process is confusing to me and always has been,
and I'll try to explain why. (My *own* way of describing it is the opposite, as
"rgb to srgb"). Perhaps it's simply a difference in wording, between a user's
perspective vs. the actual math process itself.

When picking a color visually in a gamma 2.2 color-picker (like Photoshop),
the color appears a certain way there. Let's say I pick a shade of green. The
actual values in PS are in the 0-255 range, like <104,230,75>/255. Although the
*visual* color I see there is a gamma-bent version of the vector values, the
values themselves are linear-- at least, that is what I have always understood
them to be.

Bringing those values into POV-ray, and initially using them as RGB
<104,230,75>/255, means to me that they are again simply being treated as
*linear* values (and the color is 'washed out' in appearance, compared to
Photoshop.) So, I apply the srgb keyword to re-create the color I originally
saw. But the initial <104,230,75>/255 color vector is itself linear-- which is
the color being given to the 'srgb math' that's internal to POV-ray. In other
words, the initial color is still RGB, not (yet) an 'SRGB version'.

So why is the process instead called "srgb-to-rgb conversion"? The initial
'input color' is linear RGB. I do understand that the final 'processed' color is
again RGB-- it started as RGB values, underwent an 'srgb gamma transformation'
under-the-hood, then emerged as a 'new' RGB color.

So is the term "srgb to rgb" actually just a description of the internal
operation being performed, and the math there? The way I see it is, "rgb color
converted by the srgb process". Thus the confusion-- from a user's perspective,
anyway.

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