[Image-SIG] How to apply a threshold value to the image
Fredrik Lundh
fredrik at pythonware.com
Sat Nov 10 11:44:55 CET 2007
export at hope.cz wrote:
> But how should the 256-item mapping table look like, if the
> threshold is 18( found from the histogram)
here's one way to do it:
threshold = 18
table = []
for i in range(256):
if i < threshold:
table.append(0) # black
else:
table.append(255) # white
out = im.point(table)
there are shorter ways to write this; the above was written for clarity.
quite often, passing in a function instead of a table can make the
code shorter:
threshold = 18
def map(i):
if i < threshold:
return 0
return 255
out = im.point(table)
there are plenty of ways to do this in one line as well, but I'll leave
that as an exercise.
</F>
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