How to estimate base color from photos?

bitinn

Hi,

Say I want to extract base color (for PBR texturing, using metallic approach) from a photo, where materials are clearly affected by lighting. How to do so more accurately?

I am not certain how this problem is solved commonly. Through experience? Through better reference photos? Is there a methodology I can use to achieve better result?

ExcessiveZero

well there is a degree of falloff but a few things we can likely establish is that the base color values are likely all even, if you want to be pedantic to get the true base colour I would say sample the front boxes in the least ammount of direct light then take the shadowed and unshadowed diffuse spots around the boxes, and adjust the values against the shadow lightening the base diffuse 
that would be my approach at least if I was being pedantic.

otherwise I would just say trust your artistic eye, keep the levels and exposure consistent and do comparisons as you adjust the color.

bitinn

ExcessiveZero said:

well there is a degree of falloff but a few things we can likely establish is that the base color values are likely all even, if you want to be pedantic to get the true base colour I would say sample the front boxes in the least ammount of direct light then take the shadowed and unshadowed diffuse spots around the boxes, and adjust the values against the shadow lightening the base diffuse 
that would be my approach at least if I was being pedantic.

otherwise I would just say trust your artistic eye, keep the levels and exposure consistent and do comparisons as you adjust the color.

Cheers!

I was told a few times to not "eyeball estimate things" on this forum, glad to hear at least in some instances I can trust my eyes

Neox

well if you can not research the values, what are you supposed to do? you gotta eyeball it, or you find out who is the manufacturer of these pieces and check their catalogue for infos regarding colors. With the metallic approach there is only 2 values you have to worry about here, roughness and albedo, one of them is just greyscale.

I think if you can not research it, build the scene, match the lighting and then start working on the materials to match the reference.

Bletzkarn

Generally what you would do is take a photo with a color checker, chrome sphere and matte sphere in the same image.

The color checker balances the photo to a more "true" colour hue. The spheres help to determine light direction, intensity, GI and HDR image.

They then recreated the lighting conditions in a 3D program and baked maps that cancelled out the natural lighting conditions of the environment, then an artist would do touch-up. So even a procedure like this requires some artist eye.

The only way to actually get the base color is to use a material scanner (extremely controlled environment) which.. are expensive and rare.

So most of the time - you are guessing. Which is why it's "3D artist".

Bletzkarn

In most cases a color checker will do more than enough if it's a fairly matte material.

JordanN

Even before the PBR workflow went mainstream, I found the existence of the diffuse/albedo texture made more sense, when you think of its relation to local light sources.

No object in life is naturally brown, blue, purple etc. What we're seeing are rays of light hit an object and then it bounces back into our eyes. It's why if you took out a purple lightbulb and shine it on a white piece of paper, the paper's texture didn't become purple. It simply shined back those [purple] rays.

What the PBR model did was standardize this process so the textures should look scientifically accurate in all lighting scenarios. Like how only Coal material has a really dark albedo, because black absorbs a lot of light, whereas White Paint is going to be more lighter, because white reflects light.

RN

If you know the local colour of an element of the photo, that is, what it should look like under a neutral light (no saturation), then you can colour-adjust the photo until that element goes from its "veiled colour" (affected by lighting) back to its "local colour" (unaffected).

This process is called white balancing.

Edit: this is useful too:
https://en.wikipedia.org/wiki/White_point#White_point_conversion

bitinn

Alright, I think the consensus is "in most cases you have to manually adjust it anyway, plus PBR metallic only have 2 sliders", thx all for your inputs!

Menchen

Albedo is not really that hard to get, also it allows for wider error range. Roughness is the real pain to get accurately.