Martin wrote:
> Dear group
>
> I'm trying to use PIL to write an array (a NumPy array to be exact) to
> an image.
> Peace of cake, but it comes out looking strange.
>
> I use the below mini code, that I wrote for the purpose. The print of
> a looks like expected:
>
> [[ 200. 200. 200. ..., 0. 0. 0.]
> [ 200. 200. 200. ..., 0. 0. 0.]
> [ 200. 200. 200. ..., 0. 0. 0.]
> ...,
> [ 0. 0. 0. ..., 200. 200. 200.]
> [ 0. 0. 0. ..., 200. 200. 200.]
> [ 0. 0. 0. ..., 200. 200. 200.]]
>
> But the image looks nothing like that.
>
> Please see the images on:
> http://hvidberg.net/Martin/temp/quat_col.png
> http://hvidberg.net/Martin/temp/quat_bw.png
>
> or run the code to see them locally.
>
> Please – what do I do wrong in the PIL part ???
>
> :-? Martin
>
>
>
> import numpy as np
> from PIL import Image
> from PIL import ImageOps
>
> maxcol = 100
> maxrow = 100
>
> a = np.zeros((maxcol,maxrow),float)
>
> for i in range(maxcol):
> for j in range(maxrow):
> if (i<(maxcol/2) and j<(maxrow/2)) or (i>=(maxcol/2) and j>=
> (maxrow/2)):
> a[i,j] = 200
> else:
> a[i,j] = 0
>
> print a
>
> pilImage = Image.fromarray(a,'RGB')
> pilImage.save('quat_col.png')
> pilImage = ImageOps.grayscale(pilImage)
> pilImage.save('quat_bw.png')
The PIL seems to copy the array contents directly from memory without any
conversions or sanity check. In your example The float values determine the
gray value of 8 consecutive pixels.
If you want a[i,j] to become the color of the pixel (i, j) you have to use
an array with a memory layout that is compatible to the Image.
Here are a few examples:
>>> import numpy
>>> from PIL import Image
>>> a = numpy.zeros((100, 100), numpy.uint8)
>>> a[:50, :50] = a[50:, 50:] = 255
>>> Image.fromarray(a).save("tmp1.png")
>>> b = numpy.zeros((100, 100, 3), numpy.uint8)
>>> b[:50, :50, :] = b[50:, 50:, :] = [255, 0, 0]
>>> Image.fromarray(b).save("tmp2.png")
>>> c = numpy.zeros((100, 100), numpy.uint32)
>>> c[:50, :50] = c[50:, 50:] = 0xff808000
>>> Image.fromarray(c, "RGBA").save("tmp3.png")
Peter
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