thumbnail creation crashes in easy_thumbnails.processors.background

I am using Django and easy-thumbnails 2.3. My intention is to take an image, scale it down so that it fits a square and fill the empty area with white color in case of non-square original images. Also in case of transparent images the transparency shall be changed to white.

My settings.py contains the following lines:

THUMBNAIL_PROCESSORS = (
    'easy_thumbnails.processors.colorspace',
    'easy_thumbnails.processors.autocrop',
    'easy_thumbnails.processors.scale_and_crop',
    'easy_thumbnails.processors.filters',
    'easy_thumbnails.processors.background',
)

THUMBNAIL_ALIASES = {
    '':{            
        'square_image': {'background':'#fff','replace_alpha':'#fff','size':(200,200)},
        },
    }

THUMBNAIL_TRANSPARENCY_EXTENSION = 'jpg'

I've tried some debugging and everything seems to work quite well and makes sense until the code reaches a line 318 in the background-processor function of easy-thumbnails processors.py:

im = colorspace(im, replace_alpha=background, **kwargs)

Here the debugger returns straight to the method that was calling background(im, size, background=None, **kwargs).

Is there anything wrong with my configuration of square_image in THUMBNAIL_ALIASES? Could it be anything else?

Solution

It turns out that you can't use 'background':'#fff' from the background processor and 'replace_alpha':'#fff' from the colorspace processor at the same time, as the background-key is turned into replace_alpha in

im = colorspace(im, replace_alpha=background, **kwargs)

and then you end up with two replace_alpha, as one is still in **kwargs. This causes the error. But it also turns out that in

THUMBNAIL_ALIASES = {
    '':{            
        'square_image': {'background':'#fff','replace_alpha':'#fff','size':(200,200)}, #wrong
        },
    }

you don't even need replace_alpha. The background processor does not add bars at the sides of a non-fitting image, but instead the image gets written on a - in my case white - background. The colorspace conversion does not seem to happen before that. So the proper definition would be

THUMBNAIL_ALIASES = {
    '':{            
        'square_image': {'background':'#fff','size':(200,200)},
        },
    }