scipy imsave saves wrong values

Question

I\'m trying to write code that will produce disparity maps using numpy and scipy, but the values that I store in my numpy array for my images are completely different from t

Answer 1

The data gets rescaled when the dtype of the array is changed from np.float64 (the data type of disp12im) to the 8 bit values stored in the image.

To avoid this, convert your image to data type np.uint8 before giving it to imsave:

misc.imsave('disp121.pgm', disp12im.astype(np.uint8))

For example, I'll save this x as a PGM image:

In [13]: x
Out[13]: 
array([[  1.,   3.,   5.],
       [ 21.,  23.,  25.]])

In [14]: x.dtype
Out[14]: dtype('float64')

Save x unaltered, and then read it back:

In [15]: imsave('foo.pgm', x)

In [16]: imread('foo.pgm')
Out[16]: 
array([[  0,  21,  42],
       [212, 234, 255]], dtype=uint8)

The values have been scaled up to the full 8-bit range.

Instead, convert x to np.uint8 before saving, and then read it back:

In [17]: imsave('foo.pgm', x.astype(np.uint8))

In [18]: imread('foo.pgm')
Out[18]: 
array([[ 1,  3,  5],
       [21, 23, 25]], dtype=uint8)