pillow-grayscale

name	pillow-grayscale
description	Convert images to grayscale in-place using Pillow (PIL), overwriting original RGB files.

Pillow Grayscale Conversion

Installation

pip install Pillow

Convert Single Image In-Place

from PIL import Image

def convert_to_grayscale_inplace(image_path):
    img = Image.open(image_path)
    gray = img.convert("L")      # "L" mode = 8-bit grayscale
    gray.save(image_path)        # overwrite the original file

Convert Multiple Images

from PIL import Image
import glob

def batch_convert_grayscale(pattern):
    for path in glob.glob(pattern):
        img = Image.open(path).convert("L")
        img.save(path)

Modes Reference

Mode	Description
"L"	8-bit grayscale (0-255)
"RGB"	24-bit color
"RGBA"	32-bit color with alpha
"1"	1-bit black & white

Notes

• .convert("L") handles all source formats (RGB, RGBA, etc.)
• Saving back to PNG preserves lossless quality
• After conversion, the file on disk is grayscale but retains the .png extension
• OpenCV's cv2.imread() will still read the file; use cv2.IMREAD_GRAYSCALE or the image will have 3 identical channels