Google-app-engine – How Do I Convert Palette-Based PNG with Transparency To RGB in PIL

google-app-enginegoogle-cloud-storageimagepngpython-imaging-library

I'm currently building a site in app engine that uploads images to google cloud storage and to complete basic manipulations I'm using python's PIL

I've been having problems with the following image which another stackoverflow member has mentioned is a palette-based PNG with transparency, which I've been reading may be a bit buggy in PIL

My question is really a back to basics one: What is the best way to convert this to an RGB format with transparent pixels set to #FFF? I've been able to get it to work through a combined RGBA then RGB paste but that seems redundant

However, for a direct conversion I'm getting a bad transparency mask i.e. using the solution from PIL Convert PNG or GIF with Transparency to JPG without

Also if anybody has ideas why the image degrades to terrible quality after conversion, that's entirely a bonus for me!

Best Answer

A way to do this is to first convert the file to jpg -- seems like a problem with the png encoding (or something related to that)

Related Solutions

Python – How to resize an image using PIL and maintain its aspect ratio

Define a maximum size. Then, compute a resize ratio by taking min(maxwidth/width, maxheight/height).

The proper size is oldsize*ratio.

There is of course also a library method to do this: the method Image.thumbnail.
Below is an (edited) example from the PIL documentation.

import os, sys
import Image

size = 128, 128

for infile in sys.argv[1:]:
    outfile = os.path.splitext(infile)[0] + ".thumbnail"
    if infile != outfile:
        try:
            im = Image.open(infile)
            im.thumbnail(size, Image.ANTIALIAS)
            im.save(outfile, "JPEG")
        except IOError:
            print "cannot create thumbnail for '%s'" % infile

Replace transparency in PNG images with white background

-background white -alpha remove -alpha off

Example:

convert image.png -background white -alpha remove -alpha off white.png

Feel free to replace white with any other color you want. Imagemagick documentation says this about the -alpha remove operation:

This operation is simple and fast, and does the job without needing any extra memory use, or other side effects that may be associated with alternative transparency removal techniques. It is thus the preferred way of removing image transparency.

Best Answer

Related Solutions

Python – How to resize an image using PIL and maintain its aspect ratio

Replace transparency in PNG images with white background

Related Topic