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copied!<p>If I understood correctly the <code>-level</code> option of ImageMagick, then the <code>level_image</code> function I provide should do what you want.</p> <p>Two things to note:</p> <ul> <li>the speed definitely can be improved</li> <li>it currently only works with RGB images</li> <li>the algorithm goes through the HSV colorspace, and affects only the V (brightness) component</li> </ul> <p>The code:</p> <pre><code>import colorsys class Level(object): def __init__(self, minv, maxv, gamma): self.minv= minv/255.0 self.maxv= maxv/255.0 self._interval= self.maxv - self.minv self._invgamma= 1.0/gamma def new_level(self, value): if value <= self.minv: return 0.0 if value >= self.maxv: return 1.0 return ((value - self.minv)/self._interval)**self._invgamma def convert_and_level(self, band_values): h, s, v= colorsys.rgb_to_hsv(*(i/255.0 for i in band_values)) new_v= self.new_level(v) return tuple(int(255*i) for i in colorsys.hsv_to_rgb(h, s, new_v)) def level_image(image, minv=0, maxv=255, gamma=1.0): """Level the brightness of image (a PIL.Image instance) All values ≤ minv will become 0 All values ≥ maxv will become 255 gamma controls the curve for all values between minv and maxv""" if image.mode != "RGB": raise ValueError("this works with RGB images only") new_image= image.copy() leveller= Level(minv, maxv, gamma) levelled_data= [ leveller.convert_and_level(data) for data in image.getdata()] new_image.putdata(levelled_data) return new_image </code></pre> <p>If there is some way to do the RGB→HSV conversion (and vice versa) using PIL, then one can split into the H, S, V bands, use the <code>.point</code> method of the V band and convert back to RGB, speeding up the process by a lot; however, I haven't found such a way.</p>

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