PIL Image can't open png file with "I"?

[Fredrik Lundh]

"James Hu" wrote:

> I have png file with mode "I", 16 bit,
> And I tried to open it with im=Image.open("output.png"), im.show()
> I got all white image.
> Don't why?

because all of 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)

</F>