Image Converter

Convert, resize, compress, and optimize images with Python Pillow.

Quick Start

from PIL import Image import pillow_heif

Register HEIF/HEIC support

pillow_heif.register_heif_opener()

img = Image.open("input.heic") img.save("output.jpg", quality=85, optimize=True)

Dependencies

pip install pillow pillow-heif

Format Conversion

Supported Formats

Format Read Write Notes

JPEG/JPG Yes Yes Lossy, best for photos

PNG Yes Yes Lossless, supports transparency

WebP Yes Yes Modern web format, excellent compression

HEIC/HEIF Yes No* Apple format, requires pillow-heif

GIF Yes Yes Animation support

TIFF Yes Yes Lossless, large files

BMP Yes Yes Uncompressed

AVIF Yes Yes* Best compression, requires pillow-avif-plugin

*Limited support, check library versions

Mode Conversion

RGBA (with alpha) -> RGB (for JPEG)

if img.mode in ('RGBA', 'LA', 'P'): img = img.convert('RGB')

RGB -> Grayscale

gray = img.convert('L')

Grayscale -> RGB

rgb = gray.convert('RGB')

Resizing & Downscaling

Proportional Resize

Resize by percentage

scale = 0.5 # 50% new_size = (int(img.width * scale), int(img.height * scale)) resized = img.resize(new_size, Image.LANCZOS)

Resize to max dimension (preserve aspect ratio)

max_dim = 1920 ratio = min(max_dim / img.width, max_dim / img.height) if ratio < 1: new_size = (int(img.width * ratio), int(img.height * ratio)) resized = img.resize(new_size, Image.LANCZOS)

Thumbnail (in-place, efficient)

img.thumbnail((800, 800), Image.LANCZOS) # Modifies in-place

Resampling Filters

Image.LANCZOS
Best quality, slower (recommended for downscaling)
Image.BICUBIC
Good quality, faster
Image.BILINEAR
Medium quality
Image.NEAREST
Fastest, pixelated (good for pixel art)

Compression & Optimization

JPEG Quality

Quality 1-100 (80-85 is good balance)

img.save("out.jpg", quality=85, optimize=True)

Progressive JPEG (loads gradually)

img.save("out.jpg", quality=85, optimize=True, progressive=True)

PNG Optimization

Maximum compression

img.save("out.png", optimize=True, compress_level=9)

Reduce colors for smaller file (256 colors max)

quantized = img.quantize(colors=256) quantized.save("out.png", optimize=True)

WebP (best for web)

Lossy (like JPEG)

img.save("out.webp", quality=85, method=6)

Lossless (like PNG but smaller)

img.save("out.webp", lossless=True, quality=100)

Batch Processing

See scripts/batch_convert.py for full batch processing with:

Parallel processing with concurrent.futures
Progress reporting
Error handling
Multiple output formats

Basic Batch Pattern

from pathlib import Path from concurrent.futures import ThreadPoolExecutor

def convert_image(path, output_dir, target_format, quality=85): img = Image.open(path) if img.mode != 'RGB': img = img.convert('RGB') output = output_dir / f"{path.stem}.{target_format}" img.save(output, quality=quality, optimize=True) return output

input_dir = Path("./images") output_dir = Path("./converted") output_dir.mkdir(exist_ok=True)

files = list(input_dir.glob("*.png")) with ThreadPoolExecutor(max_workers=4) as executor: results = list(executor.map( lambda f: convert_image(f, output_dir, "jpg"), files ))

Metadata & EXIF

Strip All Metadata

Create clean image (removes ALL metadata including ICC profile)

clean = Image.new(img.mode, img.size) clean.putdata(list(img.getdata())) clean.save("clean.jpg", quality=85)

Strip EXIF Only (preserve ICC color profile)

icc = img.info.get('icc_profile') if 'exif' in img.info: del img.info['exif'] img.save("out.jpg", quality=85, icc_profile=icc)

Handle EXIF Orientation

from PIL import ImageOps img = ImageOps.exif_transpose(img) # Auto-rotate based on EXIF

Watermarking

from PIL import Image, ImageDraw, ImageFont

def add_watermark(img, text, opacity=128): watermark = Image.new('RGBA', img.size, (0, 0, 0, 0)) draw = ImageDraw.Draw(watermark)

# Use default font or specify path
try:
    font = ImageFont.truetype("/System/Library/Fonts/Helvetica.ttc", 36)
except:
    font = ImageFont.load_default()

bbox = draw.textbbox((0, 0), text, font=font)
text_width = bbox[2] - bbox[0]
text_height = bbox[3] - bbox[1]

x = img.width - text_width - 20
y = img.height - text_height - 20

draw.text((x, y), text, font=font, fill=(255, 255, 255, opacity))

if img.mode != 'RGBA':
    img = img.convert('RGBA')

return Image.alpha_composite(img, watermark)

Common Tasks

HEIC to JPEG (iPhone photos)

import pillow_heif pillow_heif.register_heif_opener()

img = Image.open("photo.heic") img = ImageOps.exif_transpose(img) # Fix orientation if img.mode != 'RGB': img = img.convert('RGB') img.save("photo.jpg", quality=85, optimize=True)

Optimize for Web

def optimize_for_web(input_path, output_path, max_width=1920, quality=85): img = Image.open(input_path) img = ImageOps.exif_transpose(img)

# Resize if too large
if img.width > max_width:
    ratio = max_width / img.width
    new_size = (max_width, int(img.height * ratio))
    img = img.resize(new_size, Image.LANCZOS)

# Convert mode
if img.mode in ('RGBA', 'P'):
    img = img.convert('RGB')

# Strip metadata
icc = img.info.get('icc_profile')

# Save optimized
img.save(output_path, quality=quality, optimize=True,
         progressive=True, icc_profile=icc)

Create Thumbnails

def create_thumbnail(input_path, output_path, size=(300, 300)): img = Image.open(input_path) img = ImageOps.exif_transpose(img) img.thumbnail(size, Image.LANCZOS)

if img.mode != 'RGB':
    img = img.convert('RGB')

img.save(output_path, quality=85, optimize=True)

File Size Comparison

Format Typical Size Best For

JPEG 85% 100% baseline Photos

WebP 85% ~30% smaller Web images

PNG 2-5x larger Graphics with transparency

AVIF 85% ~50% smaller Next-gen web

HEIC ~50% smaller Apple ecosystem

Scripts

scripts/batch_convert.py
Full-featured batch converter with CLI
scripts/optimize_web.py
Web optimization with size targets

image-converter

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