Am 10.01.2011 22:57, schrieb Kenneth:

> I've lately discovered that I can get a gamma 1.0 color-picker in my (old)
> version of Photoshop: changing the gamma of its image display to 1.0 (under
> FILE/COLOR SETTINGS/RGB SETUP) also changes the shades in the color-picker.
> Nice! (I don't know why I never noticed that before--or maybe I thought it was a
> bug!!) From what I see, an identical(?) color and shade *can* be chosen
> there--relative to gamma 2.2 space--just in a different location in the color
> field. So this set-up could be used successfully; but a little stand-alone app
> would be more convenient, less resource-intensive--and built 'from the ground
> up' to work this way.

I'd say, a dialog in the POV-Ray GUI would be best for such a purpose. 
(Of course that doesn't help Unix users. But I guess if you find a good 
stand-alone color picker app there, you're likely to get the source code 
as well, so modification for gamma 1.0 should be no big deal.)

> Is my Photoshop gamma-change example even a 'technically legitimate/accurate'
> way of doing this? It seems that an *almost*-identical color can be chosen re:
> gamma-2.2 space, but perhaps not 100-percent accurately. At least, that's what
> my eyes tell me, as well as the color-picker numbers: the color match is
> extremely close, but not spot-on. (It may be that certain subtle shades of color
> are simply missing from this model--OR that I'm just not being careful enough!)

The photoshop gamma change /should/ do the trick. Don't know why they 
should be not spot-on.

> So another question arises: Which of the following two choices would produce the
> more accurate/correct color rendition in v3.7 with assumed_gamma 1.0:
>
> 1) picking the color from Photoshop's (or colscr32's) 'typical' gamma 2.2 color
> space and using srgb<.....>  to convert it?
>   OR
> 2) picking the color from a gamma 1.0 space (not necessarily Photoshop's) and
> using rgb<......>  with no conversion?

In theory, with a perfectly calibrated display and all, 2) would give 
more accurate results. Note however that various versions of Photoshop 
do not exactly default to a gamma 2.2, but to sRGB color space - in 
which case 1) and 2) should be fully equivalent - and that typically 
displays are a bit off anyway.

> In other words, is a gamma-1.0 color-picker even necessary??

To be frank, I don't think so. That's what the srgb(f,t) keywords were 
introduced for. (BTW they're designed to actually work regardless of 
assumed_gamma setting.)

But a built-in color picker in the POV-Ray GUI, giving colors in the 
fitting range, with "auto-paste" functionality, would be nice anyway.

> I'll admit that there are many POV-Ray images from the past that look absolutely
> great and stunning, using assumed_gamma 1.0. In pre-v3.7 days, how did these
> artists choose colors that would look good? (That is, 'visually pleasing' colors
> that would match what a color-picker in 2.2 gamma space would show.)  Did others
> simply use the rather cumbersome power-law trick? I.e., instead of rgb
> <.4,.8,.6>, using<pow(.4,2.2),pow(.8,2.2),pow(.6,2.2)>? I'm curious as to what
> technique(s) have been so successfully used before now.

I guess typically they would have used tweaking colors until they looked 
good. At least that's how I used to do it.

Post a reply to this message