Reversing the effects of bleach bypass

[Katie Boundary]

"Bleach bypass" is a technique that sucks most of the color saturation out of an image and obliterates detail in very light and very dark areas. If you've ever seen Supernatural, Aliens Vs. Predator Requiem, or Terminator Salvation, then you know what I'm talking about.

I'm interested in undoing this effect and making the image look as normal as possible. Obviously, part of the solution is to just increase the saturation. But I'm not sure how to fix the brightness/contrast issue. Is there a brightness/contrast rescaler that increases contrast in very light and very dark areas, and decreases the dynamic range of the medium-brightness areas?

[poisondeathray]

Is there a brightness/contrast rescaler that increases contrast in very light and very dark areas, and decreases the dynamic range of the medium-brightness areas?

Dogway has a contrast function ex_contrast() in the GradePack, and negative values will be like a "reverse S curve". Dither_sigmoid_inverse from dither tools also works similarly. Dogway's has better pixel format support natively. Both have adjustable center (pivot point)

[Dogway]

Depends on the image but if the bleach effect is more like local contrast you would be better doing a deconvolution. Try ex_unsharp() with negative values at different frequencies ('Fc')

[johnmeyer]

I am not an expert in color, but someone who is should comment on what colorspace you should use. This is important because of color, saturation, and luma values interact. If you are in the wrong colorspace, I am not sure you would be able to fully reverse the transformation.

[Katie Boundary]

Dogway has a contrast function ex_contrast() in the GradePack, and negative values will be like a "reverse S curve". Dither_sigmoid_inverse from dither tools also works similarly.

Gradepack requires ExTools as a dependency, and ExTools says it only works with AVIsynth+, not regular AVIsynth.

Dither Tools says it's only for high-bit-depth content. I'm working with normal bit depths.

If you are in the wrong colorspace, I am not sure you would be able to fully reverse the transformation.

It doesn't need to be perfect, it just needs to not look like shit.

[poisondeathray]

Dither Tools says it's only for high-bit-depth content. I'm working with normal bit depths.


It's ok - it's converted to stack 16bit for the filters, then back down to 8bit. This is what people used back when avisynth classic was 8bit only, before other pixel formats were introduced

Or you could upgrade to avs+. Many improvements, very stable now

[StainlessS]

Katie, Avs+ current, is really quite stable and better/faster than avs standard.
Worth a try unless you use some really old plugs, eg v2.0 C plugs dont work I think.
(MeGUI requires updated AvsWrapper for Avs+)

[Katie Boundary]

I'm happy to report that smoothcurve(Ycurve="0-0;32-48;224-208;255-255").tweak(sat=2.0) is working beautifully for Supernatural. I haven't tested it on Terminator Salvation or AvP: Requiem but I'm optimistic.