Add contrast Normalization

[Charles-Schleich]

Ive begun to implement a contrast normalization function, based on the README's wikipedia entry wiki

I figure the imageproc crate is the right place to put it.

I will update the README when i am done.

[vadixidav]

You can either add it to imageproc (not maintained by us) or to ndarray-vision (maintained by us). imageproc is more mature, so that's a great place to add it.

[Charles-Schleich]

Great stuff,
I don't mind putting the code in 2 places but then maintaining it might become a mission.

I've implemented the linear and non-linear versions of the function for a image::Luma input, I need to write some decent tests.

Does it make sense that a the normalization operation should also be implemented on a image::Rgb /image::Bgr image as well ?
i.e. one set of max/min input, but normalize each channel independently.
Is this something useful / needed for colour images ?

[xd009642]

Well implementing on each channel could be analogous to doing transformations on the colour curves on an image in things like gimp/photoshop I think... Not something I've seen useful in computer vision but for creative things sure. Maybe for other formats like HSV or YCrCb where there's a channel for brightness/gamma normalising that and not the others has more use.

Also as ndarray-vision exposes ndarray directly there might already be functionality in ndarray or some other crates in it's ecosystem to do that - I'm not sure. But we do have histogram equalisation for contrast enhancement, maybe we already have some of the component parts (I'd have to check)