roop wrote:
> I was browsing ImageEnhace.py, and found something that I thought was
> odd in class Contrast:
>
> class Contrast(_Enhance):
> "Adjust image contrast"
> def __init__(self, image):
> self.image = image
> mean = reduce(lambda a,b: a+b, image.convert("L").histogram())/
> 256.0
> self.degenerate = Image.new("L", image.size, mean).convert
> (image.mode)
>
> Isn't reduce(lambda a,b: a+b, image.convert("L").histogram()) the same
> as (image.size[0] * image.size[1]) - just count the number of pixels
> in the image? (Afaik, the histogram is a list of 256 elements where
> the ith element gives the number of pixels with i as the pixel value
> (0 <= i < 256)). Is this actually fishy or have I got it all muddled
> up?
>
> Thanks,
> roop
Good catch [I'll send a copy to the imaging sig]. If you replace class
Contrast like this:
class Contrast(ImageEnhance._Enhance):
"Adjust image contrast"
def __init__(self, image):
self.image = image
w, h = image.size
mean = sum(n * c for n, c in enumerate(
image.convert("L").histogram())
) / float(w * h)
self.degenerate = Image.new("L", image.size,
mean).convert(image.mode)
You should get a working Contrast class.
There _is_ another possibility:
class Contrast(ImageEnhance._Enhance):
"Adjust image contrast"
def __init__(self, image):
self.image = image
clone = image.copy()
clone.thumbnail((1, 1))
self.degenerate = clone.resize(image.size)
The former goes to a grey point, while the latter goes to
the picture's color center. I'm not quite sure which one
is more properly called "contrast," as I can see wanting
either one.
--Scott David Daniels
scott.dani...@acm.org
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