PyGame: Applying transparency to an image with alpha?

Question

I want to display an image with alpha with a specified transparency, but can't figure out how to do it.

To elaborate on how I'm struggling with this, the blurb below is a slightly modified hunk of code from this SO answer, but if you run it, you'll see that "image" loses it's native alpha, while the alpha of "image2" never changes! Yuck.

#!/usr/bin/env python

import pygame, sys

pygame.init()

window = pygame.display.set_mode((200, 200))
background = pygame.Surface((window.get_size()))
background.fill((255, 255, 255))
image = image2 = pygame.image.load('alpha.png')

image = image.convert()
rect = image.get_rect()

image2 = image2.convert_alpha()
rect2 = image2.get_rect()

rect2.left = rect.width + 1

i = 0
while True:
  for event in pygame.event.get():
    if event.type == 12:
      pygame.quit()
      sys.exit()

  image.set_alpha(i)
  image2.set_alpha(i)

  window.fill((255, 255, 255))
  window.blit(background, background.get_rect())
  window.blit(image, rect)
  window.blit(image2, rect2)

  if i == 255:
    i = 0
  else:
    i += 1

  pygame.display.update()
  pygame.time.Clock().tick(60)

So ... how is it done?

Answer 1

Make a copy of the image you want to show (to not change the original) and use following:

self.image = self.original_image.copy()
# this works on images with per pixel alpha too
alpha = 128
self.image.fill((255, 255, 255, alpha), None, pygame.BLEND_RGBA_MULT)

Sorry, to not provide a full example.

Answer 2

For what it's worth, I've seen varying results depending on the image itself. In my situation, I found that using Gimp to change the image allowed me to keep the code simple:

image = pygame.image.load('path/to/my.png').convert()
image.set_alpha(128)
surface.blit(image, (0, 0))

Using that code, the following sprites just don't work right: http://www.spriters-resource.com/resources/sheets/47/50365.png

However, it does work after using Gimp to change 2 things:

1. Image -> Mode -> Convert to Color Profile... and use the defaults
2. Image -> Mode -> Indexed... and use the defaults

After saving the changes, it works for me in Ubuntu. I can't post an image of the result because I'm a new user...