Python PIL Image.tostring()

Question

I'm new to Python and PIL. I am trying to follow code samples on how to load an image into to Python through PIL and then draw its pixels using openGL. Here are some line of the code:

from Image import *
im = open("gloves200.bmp") 
pBits = im.convert('RGBA').tostring()

.....

glDrawPixels(200, 200, GL_RGBA, GL_UNSIGNED_BYTE, pBits)

This will draw a 200 x 200 patch of pixels on the canvas. However, it is not the intended image-- it looks like it is drawing pixels from random memory. The random memory hypothesis is supported by the fact that I get the same pattern even when I attempt to draw entirely different images.Can someone help me? I'm using Python 2.7 and the 2.7 version of pyopenGL and PIL on Windows XP.

Answer 1

I think you were close. Try:

pBits = im.convert("RGBA").tostring("raw", "RGBA")

The image first has to be converted to RGBA mode in order for the RGBA rawmode packer to be available (see Pack.c in libimaging). You can check that len(pBits) == im.size[0]*im.size[1]*4, which is 200x200x4 = 160,000 bytes for your gloves200 image.

Answer 2

Have you tried using the conversion inside the tostring function directly?

im = open("test.bmp")
imdata = im.tostring("raw", "RGBA", 0, -1)
w, h = im.size[0], im.size[1]
glDrawPixels(w, h, GL_RGBA, GL_UNSIGNED_BYTE, imdata)

Alternatively use compatibility version:

 try:
      data = im.tostring("raw", "BGRA")
 except SystemError:
      # workaround for earlier versions
      r, g, b, a = im.split()
      im = Image.merge("RGBA", (b, g, r, a))

Answer 3

Thank you for the help. Thanks to mikebabcock for updating the sample code on the Web. Thanks to eryksun for the code snippet-- I used it in my code.

I did find my error and it was Python newb mistake. Ouch. I declared some variables outside the scope of any function in the module and naively thought I was modifying their values inside a function. Of course, that doesn't work and so my glDrawPixels call was in fact drawing random memory.