PIL : How to write array to image ???

[Martin]

On Oct 3, 11:56 pm, Peter Otten <__pete... at web.de> wrote:
> 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

Thanks All - That helped a lot...

The working code ended with:


        imga = np.zeros((imgL.shape[1],imgL.shape[0]),np.uint8)
        for ro in range(imgL.shape[1]):
            for co in range(imgL.shape[0]):
                imga[ro,co] = imgL[ro,co]
        Image.fromarray(imga).save('_a'+str(lev)+'.png')