I have 4 directories with images for an animation. I would like to take the set of images and generate a single image with the 4 images arranged into a 2x2 grid for each frame of the animation.

My code so far is:

import Image

fluid64 = "Fluid64_half_size/00"
fluid128 = "Fluid128_half_size/00"
fluid512 = "Fluid512_half_size/00" 
fluid1024 = "Fluid1024_half_size/00" 

out_image = "Fluid_all/00"

for pic in range(1, 26):
    blank_image = Image.open("blank.jpg")

    if pic < 10:
        image_num = "0"+str(pic)
    else:
        image_num = str(pic)

    image64 = Image.open(fluid64+image_num+".jpg")
    image128 = Image.open(fluid128+image_num+".jpg")
    image512 = Image.open(fluid512+image_num+".jpg")
    image1024 = Image.open(fluid1024+image_num+".jpg")
    out = out_image + image_num + ".jpg"

    blank_image.paste(image64, (0,0)).paste(fluid128, (400,0)).paste(fluid512, (0,300)).paste(fluid1024, (400,300)).save(out)

Not sure why it's not working. I'm getting the error:

Traceback (most recent call last):
  File "C:\Users\Casey\Desktop\Image_composite.py", line 24, in <module>
    blank_image.paste(image64, (0,0)).paste(fluid128, (400,0)).paste(fluid512, (
ste(fluid1024, (400,300)).save(out)
AttributeError: 'NoneType' object has no attribute 'paste'
shell returned 1

Any help would be awesome. Thanks!