Re: Gradients and parametric Curves

marshyswamp71 <samarsh@...>

Does anybody remember the short lived Mac only Binuscan Photo Retouch Pro app? It had a feature called "B-X-Ray" that was a grayscale preview mode that used some sort of inversion/solarization effect to "highlight" flaws in an image. It was as fast as a softproof preview keystroke toggle, so it was not doing anything very complex in RAM/CPU/GPU terms.

Stephen Marsh

--- In colortheory@..., "dacolorman" <dacolorman@...> wrote:

Ken Harris wrote:

In the 90s we had a similar kind of curve on Quantel Paintboxes. Parabolic, 0-255, maybe 8 cycles IIRC. It was used to check for problems on the drum scans. We aped it in photoshop, also to check scans. I still use it, on every file, for the same reason: forensic.

Some of my work is pick-up from other retouchers, and a 10 cycle parabolic shows compositing errors and changes in structure/grain nicely.
Such curves make easy work of finding dust spots and condensation on digital sensors.
They will also show problems on digital backs. Some backs grid, others quarter at higher ISOs.
It's best to foreknow and fix these kinds of problems before you start working.

Although it produces a similar look, the spectrum gradient is not nearly as effective for these purposes.
Can you elaborate on how to create & use these curve?

Andy Adams

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