Estimating or reading a final RGB value for rendered output (How To?)

Is there a way to get a quick read on what the output RGB value will be of a material + light sources for a point in a render?

Currently I’m trying to create a material and lighting setup to match a rendered yellow plastic to a photographed elment that will be overlayed on top.

I know what the RGB of the highlight, midtone, and shadow on the target photograph are, but currently I’m limited to rendering out the scene (or box-masked portion of a scene) to guess-and-check what the combination of material, node setup, and lighting will produce to try and match the two.

Surely there’s got to be a way to get a point-read of what the final output sRGB .jpeg file will be for an eye-droppered part of a scene, right?

There’s the rendered option for the viewport, it allows to very quickly get an idea of what the final render will look like.

In my world looks are one thing, and RGB values are another, is there any built in eyedropper function (default or add-on) that I haven’t discovered yet?

The color wheel widget has an eyedropper, but the final intensity and tint of the color in the render is going to be dependent on other factors like lighting and tonemapping.

If you’re trying to find a way to get this value (as it would be seen when rendering) without any actual rendering, you might be hard-pressed as I don’t think Blender uses any fancy algorithms to do such a thing (at least the color widget code doesn’t).

to see result faster
you can use the camera and render only a very small portion of your scene and then see the color you get!

happy bl

You just need to solve the rendering equation to read the final RGB color.

Blender even has a function that estimates it automatically - just press F12 :wink:


sounds like an opportunity for a badass addon :slight_smile:

just a little eyedropper tool you can drop over a 3x3 or 5x5 of 15x15 square of pixels in any viewer and get a realtime RGB read for the final render of just that little section, in the colorspace of your choosing (sRGB, AdobeRGB, etc . . . )

thanks everyone!

try this
[RGB] emitted = [RGB] object · [RGB] light · Irradiance (incoming light power)

You can calculate irradiance if you multiply light power for its quadratic attenuation factor using its distance to the object.