Agent skill

image-processing

Process images for web development — resize, crop, trim whitespace, convert formats (PNG/WebP/JPG), optimise file size, generate thumbnails, create OG card images. Uses Pillow (Python) — no ImageMagick needed. Trigger with 'resize image', 'convert to webp', 'trim logo', 'optimise images', 'make thumbnail', 'create OG image', 'crop whitespace', 'process image', or 'image too large'.

View SKILL.md on GitHub Repository
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Install this agent skill to your Project

npx add-skill https://github.com/jezweb/claude-skills/tree/main/plugins/design-assets/skills/image-processing

SKILL.md

Image Processing

Process images for web development. Generate a Pillow script adapted to the user's environment and specific needs.

Prerequisites

Pillow is usually pre-installed. If not:

bash
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
bash
# macOS sips examples
sips --resampleWidth 1920 input.jpg --out resized.jpg
sips --setProperty format webp input.jpg --out output.webp

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.

python
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.

python
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.

python
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:

python
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.

python
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.

python
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)

  1. Trim whitespace
  2. Convert to PNG (for transparency)
  3. Create favicon-sized version (thumbnail at 512px)

Prepare Hero Image for Production

Resize to max width 1920, convert to WebP, compress at quality 85.

Batch Process

For multiple images, generate a single script that loops over all files rather than processing one at a time.

Pipeline with Gemini Image Gen

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

  1. Generate with Gemini (raw PNG output)
  2. User picks favourite
  3. Optimise: resize to target width, convert to WebP, compress

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