I had some issues with transparent PNG images causing some strange effects when resized and saved with Python's PIL Image library.
As you can see, those jarring effects are hard to ignore.
The issue was I was ignoring the alpha channel during conversion and PIL didn't quite know what to do with it.
| from PIL import Image | |
| image = Image.open("some_file.png") | |
| image.convert("RGBA") # Convert this to RGBA if possible | |
| canvas = PyImage.new('RGBA', image.size, (255,255,255,255)) # Empty canvas colour (r,g,b,a) | |
| canvas.paste(image, mask=image) # Paste the image onto the canvas, using it's alpha channel as mask | |
| canvas.thumbnail([width, height], PyImage.ANTIALIAS) | |
| canvas.save(filename, format="PNG") |
It is a bit more work, but the results speak for themselves. Even the GIF image quality was improved after using this method!
You'll have top view them at 100% to see the difference.
Update 6/12/14:
I found a better way of colouring the images which had NO loss in quality (updated code above)
(Shirt design "Majin Power!" by ddjvigo)
You can easily see which one is rendered with the new code as the difference is quite noticeable.
There was a bug which replaced the whole pixel with white, which is wrong because it could be any other colour with transparency < 255.
(Here's the old code if anyone was wondering)
| image = Image.open("some_file.png") | |
| image.convert("RGBA") # Convert this to RGBA if possible | |
| pixel_data = image.load() | |
| if image.mode == "RGBA": | |
| # If the image has an alpha channel, convert it to white | |
| # Otherwise we'll get weird pixels | |
| for y in xrange(image.size[1]): # For each row ... | |
| for x in xrange(image.size[0]): # Iterate through each column ... | |
| # Check if it's opaque | |
| if pixel_data[x, y][3] < 255: | |
| # Replace the pixel data with the colour white | |
| pixel_data[x, y] = (255, 255, 255, 255) | |
| # Resize the image thumbnail | |
| image.thumbnail([resolution.width, resolution.height], Image.ANTIALIAS) | |
| image.save(filename) |
