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Description
What did you do?
I tried to convert grayscale images of different modes together
What did you expect to happen?
Conversion should scale values; for example, converting from float to 8-bit should have the values scaled by 255, converting from 8-bit to 16-bit should have the values scaled by 65535/255, etc.
What actually happened?
Values are being clamped
>>> img = Image.open('16bit_image.png')
>>> img.mode
'I'
>>> numpy.array(img)
array([[51559, 52726, 50875, ..., 30493, 30991, 29907],
[51743, 52185, 51221, ..., 30841, 29920, 30793],
[51279, 50534, 51128, ..., 31532, 30852, 30651],
...,
[28288, 27868, 28032, ..., 34367, 34235, 34312],
[26900, 27567, 28120, ..., 36229, 34607, 33399],
[27966, 28224, 27962, ..., 36223, 35851, 34477]], dtype=int32)
>>> numpy.array(img.convert('L'))
array([[255, 255, 255, ..., 255, 255, 255],
[255, 255, 255, ..., 255, 255, 255],
[255, 255, 255, ..., 255, 255, 255],
...,
[255, 255, 255, ..., 255, 255, 255],
[255, 255, 255, ..., 255, 255, 255],
[255, 255, 255, ..., 255, 255, 255]], dtype=uint8)Floating point data really doesn't go over well either
>>> img_float = Image.fromarray(numpy.divide(numpy.array(img), 2**16-1))
>>> numpy.array(img_float)
array([[0.7867399 , 0.8045472 , 0.77630275, ..., 0.46529335, 0.47289234,
0.45635158],
[0.78954756, 0.79629207, 0.78158236, ..., 0.4706035 , 0.45654994,
0.46987107],
[0.78246737, 0.7710994 , 0.7801633 , ..., 0.48114747, 0.47077134,
0.46770427],
...,
[0.4316472 , 0.42523843, 0.4277409 , ..., 0.5244068 , 0.52239263,
0.52356756],
[0.41046768, 0.42064545, 0.4290837 , ..., 0.55281913, 0.52806896,
0.50963604],
[0.4267338 , 0.43067065, 0.42667276, ..., 0.5527275 , 0.5470512 ,
0.5260853 ]], dtype=float32)
>>> img_oct = img_float.convert('L')
>>> numpy.array(img_oct)
array([[0, 0, 0, ..., 0, 0, 0],
[0, 0, 0, ..., 0, 0, 0],
[0, 0, 0, ..., 0, 0, 0],
...,
[0, 0, 0, ..., 0, 0, 0],
[0, 0, 0, ..., 0, 0, 0],
[0, 0, 0, ..., 0, 0, 0]], dtype=uint8)
>>>The input image is a 16 bit PNG made with GIMP, as attached below.
terrain_input.png
What versions of Pillow and Python are you using?
Using Python 3.6.5 and Pillow 5.1.0