image-processing

Image Processing

Use img-process (shipped in bin/) for common operations. For complex or custom workflows, generate a Pillow script adapted to the user's environment.

Quick Reference — img-process CLI

img-process resize hero.png --width 1920
img-process convert logo.png --format webp
img-process trim logo-raw.jpg -o logo-clean.png --padding 10
img-process thumbnail photo.jpg --size 200
img-process optimise hero.jpg --quality 85 --max-width 1920
img-process og-card -o og.png --title "My App" --subtitle "Built for speed"
img-process batch ./images --action convert --format webp -o ./optimised

Use img-process when: the operation is standard (resize, convert, trim, thumbnail, optimise, OG card, batch). This is faster and avoids generating a script each time.

Generate a custom script when: the operation needs logic img-process doesn't cover (compositing multiple images, watermarks, complex text layouts, conditional processing).

Prerequisites

Pillow is required for both img-process and custom scripts:

pip install Pillow

If Pillow is unavailable, use alternatives:

| Alternative | Platform | Install | Best for | |-------------|----------|---------|----------| | sips | macOS (built-in) | None | Resize, convert (no trim/OG) | | sharp | Node.js | npm install sharp | Full feature set, high performance | | ffmpeg | Cross-platform | brew install ffmpeg | Resize, convert |

Output Format Guide

| Use case | Format | Why | |----------|--------|-----| | Photos, hero images | WebP | Best compression, wide browser support | | Logos, icons (need transparency) | PNG | Lossless, supports alpha | | Fallback for older browsers | JPG | Universal support | | Thumbnails | WebP or JPG | Small file size priority | | OG cards | PNG | Social platforms handle PNG best |

Core Patterns

Save with Format-Specific Quality

Different formats need different save parameters. Always handle RGBA-to-JPG compositing — JPG does not support transparency, so composite onto a white background first.

from PIL import Image
import os

def save_image(img, output_path, quality=None):
    os.makedirs(os.path.dirname(output_path) or ".", exist_ok=True)
    kwargs = {}
    ext = output_path.lower().rsplit(".", 1)[-1]

    if ext == "webp":
        kwargs = {"quality": quality or 85, "method": 6}
    elif ext in ("jpg", "jpeg"):
        kwargs = {"quality": quality or 90, "optimize": True}
        # RGBA → RGB: composite onto white background
        if img.mode == "RGBA":
            bg = Image.new("RGB", img.size, (255, 255, 255))
            bg.paste(img, mask=img.split()[3])
            img = bg
    elif ext == "png":
        kwargs = {"optimize": True}

    img.save(output_path, **kwargs)

Resize with Aspect Ratio

When only width or height is given, calculate the other from aspect ratio. Use Image.LANCZOS for high-quality downscaling.

def resize_image(img, width=None, height=None):
    if width and height:
        return img.resize((width, height), Image.LANCZOS)
    elif width:
        ratio = width / img.width
        return img.resize((width, int(img.height * ratio)), Image.LANCZOS)
    elif height:
        ratio = height / img.height
        return img.resize((int(img.width * ratio), height), Image.LANCZOS)
    return img

Trim Whitespace (Auto-Crop)

Remove surrounding whitespace from logos and icons. Convert to RGBA first, then use getbbox() to find content bounds.

img = Image.open(input_path)
if img.mode != "RGBA":
    img = img.convert("RGBA")
bbox = img.getbbox()  # Bounding box of non-zero pixels
if bbox:
    img = img.crop(bbox)

Thumbnail

Fit within max dimensions while maintaining aspect ratio:

img.thumbnail((size, size), Image.LANCZOS)

Optimise for Web

Resize + compress in one step. Convert to WebP for best compression. Typical settings: width 1920, quality 85.

Cross-Platform Font Discovery

System font paths differ by OS. Try multiple paths, fall back to Pillow's default. On Linux, fc-list can discover fonts dynamically.

from PIL import ImageFont

def get_font(size):
    font_paths = [
        # macOS
        "/System/Library/Fonts/Helvetica.ttc",
        "/System/Library/Fonts/SFNSText.ttf",
        # Linux
        "/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf",
        "/usr/share/fonts/truetype/liberation/LiberationSans-Regular.ttf",
        # Windows
        "C:/Windows/Fonts/arial.ttf",
    ]
    for path in font_paths:
        if os.path.exists(path):
            try:
                return ImageFont.truetype(path, size)
            except Exception:
                continue
    return ImageFont.load_default()

OG Card Generation (1200x630)

Composite text on a background image or solid colour. Apply semi-transparent overlay for text readability. Centre text horizontally.

from PIL import Image, ImageDraw, ImageFont

width, height = 1200, 630

# Background: image or solid colour
if background_path:
    img = Image.open(background_path).resize((width, height), Image.LANCZOS)
else:
    img = Image.new("RGB", (width, height), bg_color or "#1a1a2e")

# Semi-transparent overlay for text readability
overlay = Image.new("RGBA", (width, height), (0, 0, 0, 128))
img = img.convert("RGBA")
img = Image.alpha_composite(img, overlay)

draw = ImageDraw.Draw(img)
font_title = get_font(48)
font_sub = get_font(24)

# Centre title
if title:
    bbox = draw.textbbox((0, 0), title, font=font_title)
    tw = bbox[2] - bbox[0]
    draw.text(((width - tw) // 2, height // 2 - 60), title, fill="white", font=font_title)

img = img.convert("RGB")

Common Workflows

Logo Cleanup (client-supplied JPG with white background)

img-process trim logo-raw.jpg -o logo-trimmed.png --padding 10
img-process thumbnail logo-trimmed.png --size 512 -o favicon-512.png

Prepare Hero Image for Production

img-process optimise hero.jpg --max-width 1920 --quality 85
# Outputs hero.webp — resized and compressed

Batch Process

img-process batch ./raw-images --action convert --format webp --quality 85 -o ./optimised
img-process batch ./photos --action resize --width 800 -o ./thumbnails

Pipeline with Gemini Image Gen

Generate images with the gemini-image-gen skill, then process them:

# After generating with Gemini (raw PNG output):
img-process optimise generated-image.png --max-width 1920 --quality 85
# Or batch process all generated images:
img-process batch ./generated --action optimise -o ./production