OK, so I'm *finally* starting to understand and appreciate the use of
assumed_gamma 1.0, after all these years of using/"abusing" 2.2. Who says old
dogs can't learn new tricks?! ;-)

Now that POV-Ray v3.7 is here, with its *recommended* use of assumed_gamma 1.0,
one of the problems that previous assumed_gamma 2.2 users (like me) are going to
have will be picking colors that look 'proper' there. (Given that we change our
*bad* behavior and go with the new gamma!) That is, colors that match what we
are used to 'seeing' in gamma 2.2 space.

Typical graphics apps have color-pickers that work in the 'standard' gamma 2.2
space--Photoshop, Painter, etc. But colors visually chosen there don't map *as
seen* into a gamma 1.0 world; they render with the typical 'washed out' look.

The color/shade shift between assumed_gamma 2.2 and 1.0 is the fundamental
reason why I've always resisted using the latter in POV-Ray, and not so much
because of the different *lighting* interaction. (I've only lately been
realizing that the odd appearance actually arises from TWO 'separate'
sources--the color shift and the pure lighting shift--and that I never separated
the two into distinct categories. I'll take it on face value that the *light*
interaction is accurate and correct in v3.7; it's solely the color shift that
concerns me.)

To solve this problem, it seems to me that it would be useful to have a little
stand-alone GUI visual color-picker app that showed its on-screen colors 'bent'
(or rather, UNbent!) into gamma 1.0 linear space, and gave us the
unprocessed/unaltered rgb equivalents. Simply put, it would AFAIU allow us to
easily pick "what we see is what we get" colors for v3.7. In other words, if a
particular gamma 2.2 color we like to use looks 'washed out' in this app, then
we simply visually choose a more pleasing color there. It's a given that the
overall 'range' of colors/shades in the picker will look 'different' from what
we're used to seeing; but that's of no consequence.

I'm aware that v3.7 has new keywords --srgb <.....> for example-- to 'convert'
colors that are chosen in typical 2.2 gamma space to 3.7's assumed_gamma 1.0
environment--and that's a wonderful addition; but I'm thinking that a
color-picker set up for gamma 1.0 might make POV-Ray code writing easier--or
perhaps more intuitive for old-time users-- by not having to deal with the new
srgb(f,t) keywords at all.  (I do realize that my old legacy scenes using
assumed_gamma 2.2 *will* need the srgb substitutions, if I want to easily update
those scenes to v3.7)

In my age-old assumed_gamma 2.2 world, I've used a free little single-purpose
Windows app called colscr32 ("color scroller") to quickly and visually choose a
color for use in POV-Ray. (Much easier than trying to figure out abstract rgb
*numbers* that might work.) It gives me the POV-Ray rgb-equivalent values from
0.0-to-1.0, like <.4,.8,.6>. That's basically the kind of simple app I have in
mind. (It's unfortunate that colscr32 isn't useful in a gamma 1.0 environment.)

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've posted a demonstration image--made for MYSELF mostly, but perhaps others
might find it enlightening as well. (Created with v3.6.2--I haven't yet
downloaded the new v3.7--but the *basic* assumptions are probably the same.) It
uses a 'bumpy' sphere model on purpose; in real life, we hardly ever see a
'plain sphere with a perfectly smooth and diffuse surface.' IMO, the middle
image looks quite good--and will probably look even better in 3.7.

But I have a fundamental question:
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!)

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

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.

In any case, doing a net search for such a specialized gamma 1.0 color-picker
app, I see that it's an old and recurring request among users of other CGI
programs; but nothing seems to be available. Any ideas for the Windows platform?
Preferably FREE, 'lightweight' and single-purpose (not GIMP or some other large
app, in other words.)

Ken

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Attachments:
Download 'color_picker_example_ken.jpg' (444 KB)

Preview of image 'color_picker_example_ken.jpg'

I agree with you.

There are currently (as far as I know) two color-pickers for POV-Ray, but 
not adapted to the newest gamma changes however. Both were made available in 
these POV-Ray newsgroups. They are POV-Ray Color Picker by Sven Littkowski 
(2006) and POVColor by Brian Allan Vanderburg II (2007).

Thomas

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> 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?

Assuming your monitor is roughly using something like gamma 2.2, this 
will work correctly.  If your monitor is too far away from sRGB then the 
internal calculations POV-ray does might result in the output hue 
looking slightly different than you expect.

In that case you should either calibrate your monitor closer to sRGB, or 
tell POV you are inputting colours (and want them displayed) using a 
different gamma curve than sRGB.  That way when you share your 
scene/image with someone else (who might have a monitor calibrated 
differently) your image should look the same.

> 2) picking the color from a gamma 1.0 space (not necessarily Photoshop's) and
> using rgb<......>  with no conversion?

A gamma 1.0 colour picker needs to know how your monitor is calibrated 
to function correctly.  It can assume sRGB, but if your monitor is not 
sRGB you will run in to the same problems as just using the srgb keyword.

So IMO it easiest (and just as correct) to simply pick colours from 
Paint/MS Office etc and then use the srgb keyword.

Post a reply to this message

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.

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"Thomas de Groot" <tDOTdegroot@interDOTnlANOTHERDOTnet> wrote:
> I agree with you.
>
> There are currently (as far as I know) two color-pickers for POV-Ray, but
> not adapted to the newest gamma changes however. Both were made available in
> these POV-Ray newsgroups. They are POV-Ray Color Picker by Sven Littkowski
> (2006) and POVColor by Brian Allan Vanderburg II (2007).
>

Thanks, Thomas!  I didn't know about those. (The original 'net search I did was
for a 'generic' gamma 1.0 color-picker; I didn't see these two POV-Ray-specific
apps mentioned, unfortunately.)

I downloaded Sven's v2.0 Color-Picker, but it seems to be bug-ridden on my
Windows XP system. (Hard to tell, actually, because it has an unconventional
user interface; but its behavior seems odd.) And AFAIK, it doesn't have a
gamma-changing feature. Do you use this app successfully? Is there a newer
version?

If my memory serves me, I may have tried downloading Vanderburg's POVColor app
in the distant past; but couldn't even get it to run. (It was probably the
source code version or something.) But I just found the Windows executable
here...

http://www.softpedia.com/downloadTag/POV-Ray+color+picker

Looks interesting on first glance, if a bit complex; but it *does* have a
gamma-changing feature. I haven't worked with it enough yet to know if that
feature works as I envisioned. I'll play around with it.

Ken

Post a reply to this message

scott <sco### [at] scottcom> wrote:

>
> A gamma 1.0 colour picker needs to know how your monitor is calibrated
> to function correctly.  It can assume sRGB, but if your monitor is not
> sRGB you will run in to the same problems as just using the srgb keyword.
>
> So IMO it easiest (and just as correct) to simply pick colours from
> Paint/MS Office etc and then use the srgb keyword.

I use a little Adobe stand-alone app called "Adobe Gamma" to tweak my monitor's
gamma (2.2); I looked at the ICC profile there, and it *is* sRGB. (Same in
Photoshop itself, BTW.) So if I understand it all correctly, I guess I'm good to
go, with *either* of the two ways of picking the colors.

Ken

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clipka <ano### [at] anonymousorg> wrote:

> I'd say, a dialog in the POV-Ray GUI would be best for such a purpose.
> [clip]
> ...a built-in color picker in the POV-Ray GUI, giving colors in the
> fitting range, with "auto-paste" functionality, would be nice anyway.

Built-in to Windows POV-Ray?!  WONDERFUL idea. I didn't dare to even suggest
that; but I have to admit that it was on my mind. ;-) Glad to see it mentioned
by someone else!

>
> Note however that various versions of Photoshop
> do not exactly default to a gamma 2.2, but to sRGB color space...

I keep forgetting that the two are not quite identical; I need to re-read all of
your WIKI material.

Do I understand that sRGB and 'vanilla' gamma 2.2 are different ICC profiles?
Sorry if that's a rather 'newbie' question; it's just difficult to keep track of
some of this arcane stuff. If they're different, which one is better for
rendering with POV-Ray using assumed_gamma 1.0?

Ken

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clipka <ano### [at] anonymousorg> wrote:
> 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.

That would be awesome!

Regards,
Dave Blandston

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"Kenneth" <kdw### [at] earthlinknet> schreef in bericht 
news:web.4d2d3693c140d037196b08580@news.povray.org...
> I downloaded Sven's v2.0 Color-Picker, but it seems to be bug-ridden on my
> Windows XP system. (Hard to tell, actually, because it has an 
> unconventional
> user interface; but its behavior seems odd.) And AFAIK, it doesn't have a
> gamma-changing feature. Do you use this app successfully? Is there a newer
> version?

I have used it for years without any trouble. My version is 2.0; no newer 
version
 afaik It has no gamma setting, so results are slightly off in POV-Ray 3.7.

> If my memory serves me, I may have tried downloading Vanderburg's POVColor 
> app
> in the distant past; but couldn't even get it to run.
snip
> Looks interesting on first glance, if a bit complex; but it *does* have a
> gamma-changing feature. I haven't worked with it enough yet to know if 
> that
> feature works as I envisioned. I'll play around with it.

It works alright for me although I have not used it much. Results are 
slightly better in 3.7 than Sven's app, probably due to the gamma 
correction.

Thomas

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> Do I understand that sRGB and 'vanilla' gamma 2.2 are different ICC profiles?

"gamma 2.2" only defines how output brightness relates to the raw pixel 
values, it is not a colour space.  sRGB specifies the exact physical 
colours that are represented by the RGB primaries, and in addition the 
function to convert from pixel values to output brightness.  That 
function is very close to gamma 2.2, but not quite.

http://en.wikipedia.org/wiki/Srgb

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