limit lavfi video filters/glsl shaders to a specific srgb range/threshold

[geextahslex]

Hi I use vf add lavfi=graph=atadenoise to denoise video. The filter is applied to the whole picture 0-255srgb. But the noise is only present in the lows 0-60srgb. So it blurrs the mids and highlights with no reason. Is it possible to limit the affected range of the video filter? This would be very usefull. It would keep details in the highlights, like faces etc.
This functionality would be very usefull not only with lavfi filters but also glsl shaders.
If this is not possible I would like to change this into a feature request :)

Thank you :)