[Image-SIG] Creating an image from <canvas>'s getImageData() data

[Fredrik Lundh]

The "raw" data decoder expects raw binary bytes; in this case, it
expects four bytes per pixel (<red> <green> <blue> <alpha>), repeated
80x80 times to fill the entire image.  What does the data you get back
from getImageData() look like if you print (a portion of) it?  e.g.
say

    print repr(data[:40])

(That "replace" you're using makes me think that you have data in text
form, not binary form...)

</F>

On Sun, Nov 23, 2008 at 7:16 PM, Adam Guthrie <ispiked at gmail.com> wrote:
> I'm using <canvas>'s getImageData() function [0] to extract pixel data
> from a canvas. The function returns a CanvasPixelArray, which is just
> a comma-separated list of all the RGBA pixel values. I then try to
> create an image using Image.fromstring as follows:
>
> data = <CanvasPixelArray from getImageData()>
> # remove the commas from the string
> data = data.replace(',', '')
> im = Image.fromstring("RGBA", (80,80), data)
> im.save("image.jpg")
>
> This all works fine without any errors. However, the resulting image
> is not the same as area that I extracted from the canvas. Here's an
> example of the resulting image:
> http://img92.imageshack.us/img92/3495/newimagept1.jpg. And here's an
> example of the expected image:
> http://img92.imageshack.us/img92/2562/graphxy9.jpg.
>
> I can't figure out what I'm doing wrong here. Does the "raw" decoder
> accept raw pixel data like this, or does it only like raw image
> formats with proper headers, etc. like BMPs. Do I need to write my own
> custom decoder?
>
> Thanks,
> Adam Guthrie
>
> [0] http://www.whatwg.org/specs/web-apps/current-work/#dom-context-2d-getimagedata
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