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On 15-7-2016 22:59, clipka wrote:
> Am 15.07.2016 um 21:06 schrieb Bald Eagle:
>> I am having, and have had in the past, difficulty reproducing the colors in
>> sampled images in my renders.
>>
>> I was wondering if anyone has had success in sampling rgb values from images or
>> "rgb color picker" apps and getting good results in their renders.
>> using sRGB doesn't seem to help me much.
>
> [snip]
>
> I haven't tested it, but you should be able to do it like this:
>
> #declare SB = 0.2; // Saturation boost
> #declare VB = 0.4; // Brightness ("volume") boost
> #declare MyColour = (( srgb <128,255,220>/255 )-SB)*(1+VB);
>
> Note that in this variant the saturation boost also affects the
> brightness, but the upside is that the formula remains simple enough to
> be written in one declaration statement, or even at the very place where
> the colour is actually used.
>
> If you are ok with something more complex but possibly easier to tweak,
> try the following:
>
> #declare SB = 0.2; // Saturation boost
> #declare VB = 0.2; // Brightness ("volume") boost
> #declare RawColour = srgb <128,255,220>/255;
> #declare SatColour = RawColour-SB;
> #declare MyColour = SatColour*(1+VB)*RawColour.gray/SatColour.gray;
>
> This should keep the general brightness unaffected by tweaks to the
> saturation.
Interesting. I am going to play with this a bit :-)
>
>
> Indirect illumination from nearby colourful surfaces, or a general
> non-uniformity in the distribution of colours in the illumination (such
> as a sunny sky, with a yellowish sun and blue sky), may introduce
> additional challenges by also affecting the hue. Countering these may
> prove particularly challenging, and you may end up tweaking each colour
> channel individually. However, the above stable-brightness trick may
> help a bit with this.
Absolutely.
>
>
> In any case, coloures picked from a simple everyday photograph (as
> opposed to a photograph taken under carefully chosen lighting
> conditions) are typically only useful as a starting point, and will
> almost inevitably need a certain degree of tweaking.
>
I was going to say this. I often 'pick' colours from photographs and
such but only as a basis for further and very substantial tweaking. An
example of one such exercise is the following fairly simple roof tile
texture based on colours picked from 'real' tiles photographs:
#declare MedTileTex =
texture {
pigment {
cells
color_map {//colours taken from roof images
[0.1 srgb <220,158,106>/255]
[0.2 srgb <217,177,126>/255]
[0.3 srgb <228,215,173>/255]
[0.4 srgb <219,152,100>/255]
[0.5 srgb <166,120, 61>/255]
[0.6 srgb <225,171,125>/255]
[0.7 srgb <230,199,142>/255]
[0.8 srgb <223,187,129>/255]
[0.9 srgb <236,176,114>/255]
[1.0 srgb <244,188,131>/255]
}
scale <1, 2, 1>*TileScale
}
normal {
average
normal_map {
[1 granite 1 scale 0.1]
[1 cells 2]
}
scale <1, 2, 1>*TileScale
}
finish {
specular 0.1
roughness 0.00286312
diffuse 0.4
reflection {0} conserve_energy
}
}
It can be used for distant view where each colour represents one tile,
or as a texture for a single tile.
--
Thomas
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