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pymagery — python imagery


1.8.0 documentation / __add__ plugin

The __add__ plugin overloads the addition operator. It allows the addition of two equally-sized images together or the addition of a constant to every pixel. If adding two RGB images together then each color channel is handled individually. If adding two monochrome images together then the result is effectively a logical OR.

The plugin prototype is (although never invoked directly):

def __add__(other)

When invoking the addition operator it should be done with the plus sign (+) just like any other addition. The following example is how two images should be added together:

import pymagery i = pymagery.image('foo.ppm') k = pymagery.image('bar.ppm') m = i + k

Every pixel in i is added to the corresponding pixel in k. If the pixel value exceeds the maximum then it is truncated to the maximum allowed value.

It is also permitted to add a constant value to every pixel:

import pymagery i = pymagery.image('foo.ppm') m = i + 20

This adds a value of 20 to every pixel. Again, if the value exceeds the maximum value then the value is truncated to the maximum. If the value falls below zero (by adding a negative value) then the value is truncated to zero. Note that 2 + i will not work because this would call int.__add__(image) and the int class does not under what an image is.

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