How to find Indexed Color mode PNGs in python

Question

How do I get a list of all the Indexed Color mode PNGs that are present in a given folder that contains a lot of other files (which are all images, but they all have different Color Modes) using Python?

Previously tried code:

from PIL import Image
import os

path = 'logos/'

for x in os.listdir (path):
    if x.endswith(".png"):
        img = Image.open(path + x)
    cmode = str(img)
    P = 'mode=P' in cmode
    if P == True:
        print (x + " " + str(img))

Using this code, I got a list of images, some of which are Indexed Color mode, and the rest are RGB color mode (checking them through Photoshop) https://www.dropbox.com/s/vlvywqhcfrkk8kq/3978.png?dl=0 This is a link to an image that shows up as P through the script, but it is an RGB image in Photoshop. https://www.dropbox.com/s/x3qiuuhs3gv9bp9/6507.png?dl=0 This is a truly Indexed Color image, like the ones that I need to find.

Answer 1

You can use this:

#!/usr/bin/env python3

from PIL import Image
from glob import glob

# Start with empty list
paletteImages = []

# Iterate over all PNGs
for f in glob("*.png"):
  # Open with PIL
  im = Image.open(f)
  # Append to list if palette image
  if 'P' in im.mode: paletteImages.append(f)

print(paletteImages)

More discussion on palette/indexed images here.

Note that the above code will also find PaletteAlpha images, i.e. those with mode = 'PA', so change in to == if you don't want PaletteAlpha images.

---

Or you can do it with ImageMagick in the Terminal more simply:

identify -verbose  *png | egrep "Filename:|Type|png.IHDR.color_type"

Filename: 3978.png
Type: PaletteAlpha
png:IHDR.color_type: 3 (Indexed)
Filename: 6507.png
Type: Palette
png:IHDR.color_type: 3 (Indexed)

Note that you can get exactly the same results from wand which is a ctypes binding to ImageMagick.

---

Or you can use pngcheck:

pngcheck *png   
                           
OK: 3978.png (64x64, 8-bit palette+trns, non-interlaced, 33.1%).
OK: 6507.png (64x64, 8-bit palette, non-interlaced, 56.3%).

You could call this with a Python subprocess.run().

---

Or you can use exiftool:

exiftool *png | egrep "Color Type|File Name"   
File Name                       : 3978.png
Color Type                      : Palette
File Name                       : 6507.png
Color Type                      : Palette

You can get the same results with the Python binding to exiftool. Example here.

---

Or you can search for the PLTE, i.e. palette PNG chunk:

grep PLTE *png     

Binary file 3978.png matches
Binary file 6507.png matches

Or you can slurp the image with Python and search for string in the slurped file to get the same result:

with open('3978.png', 'rb') as fd:
   data = fd.read()
   if b'PLTE' in data:
      print('PLTE was found')