[Image-SIG] PIL module, auto-levels adjust

[Kevin Cazabon]

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I've written a handy little module for automatically fine-tuning image files.  It will work with RGB and CMYK files, and does the following:

-checks the histogram, determines the actual brightness range used in the image for each channel

-scales the data to fill the full 0-255 range either by scaling each channel individually, or by scaling them equally (to the lowest common denomonator)


Being a certified Adobe Photoshop 4.0 instructor (by Adobe), I find the BEST way to color/density correct an image is to first set the black/white point for each of the channels individually, so that you use the entire available dynamic range.  This is basically what the module does.

The usage is as follows:

###################################

import Image
import levels

file = Image.open('filename')

file = levels.levels(file, scale_same, clip)

###################################

scale_same:  0 = scale each channel individually, 1 = scale all channels the same

clip = (integer) = if there's less than this number of pixels at the minimum/maximum brightness level found, don't use them to calculate the levels adjustment (i.e. they get clipped off the image to pure black/white)  default is 0.  This is useful if you have a few 'dark' or 'bright' pixels that actually are not relevant detail and are causing the scaling to not properly fill up the histogram.

###################################

It's not the most glamourous code, but it works very well.  It's great for batch-processing scanned images to 'tweak' the dynamic range, and do a pretty decent job at color correction too.  (most of the time, optimizing the RGB/CMYK channels to each fill the entire dynamic range does a good color correction too).

If you find it useful... please let me know!

Kevin Cazabon, B.A.A.
kcazabon@rogers.wave.ca
kcaza@cymbolic.com
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