reading images in palette mode

[Tony S Yu]

Hi Ralf,

Thanks for the feedback.

On Oct 30, 2009, at 11:31 AM, Ralf Gommers wrote:
> The images on the page you linked to can not be included I think  
> (copyright), so could you generate two small palette images (one  
> rgb, one grey, 10x10 pixels) for use in a test? (or ideally, write  
> the test:))

I couldn't easily find any palette images that weren't copyrighted; it  
never occurred to me just create them. Thanks.

> Also, I see you are already using git, so next time could you push  
> your changes to github as described here http://stefanv.github.com/scikits.image/contribute.html#development-process 
> , that would make it a bit faster to test.


I was afraid I'd have to learn git. ;)

I added the changes in three commits to: http://github.com/tonysyu/scikits.image
The first commit just adds the images, the second adds palette image  
handling + a test, and the third adds an additional test.

I wasn't sure how to test imread. I ended up checking that imread  
returns a 2D array for the grayscale palette image and a 3D array for  
the color palette image. Another possibility is to test the values of  
the array, but that seems fragile.

The last commit adds a test of the function `palette_is_gray`.  
Unfortunately, the test is a bit ugly. First, I had to add an import  
of PIL in the test, since palette_is_gray works specifically on PIL  
palette images. Second, I had to add `palette_is_grayscale` to __all__  
in pil_imread so that I could use the function in my test. (Python  
documentation suggests that __all__ only affects ``from <> import *``,  
but it seemed to prevent ``from scikits.image.io import  
palette_is_grayscale``.)

Let me know what you think of the tests. Also, should I do a pull  
request?

Best,
-Tony

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