problem with image analysis

Support Materials and Textures
1

I got a problem where i have to do some color calculations.
I try to optimize a treshold value in a vision related problem.

Essentially i have to find out a treshold value so that from RGB values B + G channel must be lower than a certain threshold, ea something in the range of 9 to 20…
And if the combined RGB value is higher the color should turn Red.

So i used below node setup in cycles.

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But i am doubting the results i get with Blender.
I guess that Mix nodes go from 0 to 254 by setting a value from 0 to 1.

2

In the divide node, the top number should be 9.0 instead of 1.0

3

But even so i get results that put me in doubts

4

0-255, the lower number would be 256? 9-20 refers to values in that 8bit range right? The clamping seems unnecessary. Maybe link the algo if it’s still borked.

Edit: If you’re checking values in the render results then I’d suggest outputting to an emission shader. Disable environment and any other lighting influences, or use an emission pass and check values there.

5

First: Cycles uses normalized color values, so there’s no need to use bits depth; just values from 0 to 1.

Second, if the threshold value is some number in a 8bit range, we need to normalize it. Let’s say that x=20 in a scale from 0 to 255; then |x|=x/255 => |x|= 0.7843

So what you really want is to check if (B+G)<(x/255), where x is your threshold value in the 0-255 scale…

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