[Image-SIG] can't show png file with mode "I"

[Fredrik Lundh]

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James Hu wrote:

> I captured image from digital camera and saved it to png file with:
>
> Image.fromstring("I", datasize, origFrame.pBuffer, 'raw', 'I;16')
>
> But when I open it  with PIL.Image
>
> im=Image.open("*.png")
> Im.show()
>
> Got white image,
> What might be the problem?

I've answered this on comp.lang.python:

    http://article.gmane.org/gmane.comp.python.general/424715

but here's the answer again, for the archives:

    maybe all pixels in the PNG file are larger than 255 ?

    show doesn't support 16-bit images, so it clamps the values down to
    an 8-bit range.  adding a

        print im.getextrema()

    will tell you what values you have in the image (it returns min and max).

    to scale things down before you display it, you can use something like:

        im = im.point(lambda x: x*(1.0/256))

    or

        lo, hi = im.getextrema()
        if lo == hi:
            im = im.point(lambda x: 128) # or something
        else:
            scale = 255.0 / (hi - lo)
            offset = -lo * scale + 0.5
            im = im.point(lambda x: x*scale + offset)

hope this helps!

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