> Hello,
>
> I would like to know if there is a way of reading the resulting pixel
> value in the rendered image as it is being rendered and if it is
> possible to overwrite it with another value. Possibly based on the
> original color.
>
> This is for testing lighting on a scene. If the color at the pixel is
> above a certain value it should be marked with another color and would
> let me know that the image is being saturated with too much light. Not a
> scientifically rigorous method but it works well for most cases.
>
> I can do this manually by just rendering, in EXR or HDR format, the
> scene using only a simple diffuse white material for all. Then, after
> rendering, load the render into a high-dynamic image viewer or editor to
> see if there are any places on the scene that are too bright.
>
> I already looked at ImageMagick but it just overkill for what I need.
>
>
>
> FlyerX

Reading a rendered pixel DURING render? Not possible without patching 
and recompiling.

I can propose some alternatives:
Render the scene with a lower light level, say, dividing all 
light_source intensity by 10 or some other value.

Have some mirror with a reflection value of 1/8, 1/32 or less showing 
the areas where you suspect are affected by clipping.



Alain

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