Fill Color of PIL Cropping/Thumbnailing

Question

I am taking an image file and thumbnailing and cropping it with the following PIL code:

        image = Image.open(filename)
        image.thumbnail(size, Image.ANTIALIAS)
        image_size = image.size
        thumb = image.crop( (0, 0, size[0], size[1]) )
        offset_x = max( (size[0] - image_size[0]) / 2, 0 )
        offset_y = max( (size[1] - image_size[1]) / 2, 0 )
        thumb = ImageChops.offset(thumb, offset_x, offset_y)                
        thumb.convert('RGBA').save(filename, 'JPEG')

This works great, except when the image isn't the same aspect ratio, the difference is filled in with a black color (or maybe an alpha channel?). I'm ok with the filling, I'd just like to be able to select the fill color -- or better yet an alpha channel.

Output example:

How can I specify the fill color?

Answer 1

Its a bit easier to paste your re-sized thumbnail image onto a new image, that is the colour (and alpha value) you want.

You can create an image, and speicfy its colour in a RGBA tuple like this:

Image.new('RGBA', size, (255,0,0,255))

Here there is there is no transparency as the alpha band is set to 255. But the background will be red. Using this image to paste onto we can create thumbnails with any colour like this:

If we set the alpha band to 0, we can paste onto a transparent image, and get this:

Example code:

import Image

image = Image.open('1_tree_small.jpg')
size=(50,50)
image.thumbnail(size, Image.ANTIALIAS)
# new = Image.new('RGBA', size, (255, 0, 0, 255))  #without alpha, red
new = Image.new('RGBA', size, (255, 255, 255, 0))  #with alpha
new.paste(image,((size[0] - image.size[0]) / 2, (size[1] - image.size[1]) / 2))
new.save('saved4.png')