Warp schrieb:
>   I do understand that. However, my point is that there are situations
> where you are not rendering for your display, but for something else
> (for example to match HTML colors, or the colors of an existing image).

For such purposes, what you need to do is to simply convert the HTML 
colors to linear values, and go with those. The output (PNG, or any 
other file format with File_Gamma=2.2, which is the de-facto internet 
standard) will then automatically match those HTML colors.

Is that so difficult?


> It seems that the ideology in POV-Ray 3.7 color handling
> is that the user must always pre-correct all color values by hand, as
> POV-Ray itself offers little help in this. Is this practical?

It is practical insofar as it would be difficult for POV-Ray to figure 
out automatically whether a color value supplied by the user is 
gamma-corrected already or not.

For instance, a user may have defined a light source and be quite happy 
with it, but now decide to split it up into two light sources set a bit 
apart and with slightly different hues.

So with linear color values, he can just write:

     light_source {
         MyLightPos - MyLightSpacing/2
         color (MyLightColour/2 + MyLightTweak)
     }
     light_source {
         MyLightPos + MyLightSpacing/2
         color (MyLightColour/2 - MyLightTweak)
     }

and get exactly the same overall scene brightness, with just a somewhat 
more lively illumination.

Would you want to do that with gamma pre-corrected values?


I do agree that it is somewhat impractical to not be able to use colors 
picked from, say, Photoshop directly in POV-Ray. But as far as that is 
concerned,

- You can easily write a macro to "gamma-un-correct" colors.

- My suggestion would be to provide a dedicated syntax for specifying 
gamma pre-corrected color values, such as:

     color rgb <0.6,0.3,0.6> gamma 2.2

(or, alternatively, a predefined macro in colors.inc or some such to 
achieve that same effect).


>   It's absolutely unreasonable for POV-Ray to not to offer any way of
> automatically gamma-correcting input images which do not have gamma
> information in them.

That is true indeed, and if the day had 36 hours I would be the first to 
implement a feature like this:

     http://bugs.povray.org/task/10

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