Image Resizer — How-To Guide

Prerequisites: Setup complete (see SETUP.md). Pillow installed.

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Table of Contents

1. How to Resize a Single Image
2. How to Compress an Image for Web or Email
3. How to Convert an Image to a Different Format
4. How to Batch Resize All Images in a Folder
5. How to Inspect an Image's Dimensions and Details
6. Automating with Cron
7. Combining with Other Skills
8. Troubleshooting Common Issues
9. Tips & Best Practices

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1. How to Resize a Single Image

What this does: Changes the pixel dimensions of an image.

When to use it: A photo from your camera is 4032×3024 (4+ MB) and you need a smaller version for email, a web page, or a profile picture.

Steps

Step 1 — Navigate to the skill directory.

cd ~/smfworks-skills/skills/image-resizer

Step 2 — Check the original image dimensions.

python3 main.py info ~/Pictures/vacation-photo.jpg

Output:

✅ Success: {'success': True, 'filename': 'vacation-photo.jpg', 'format': 'JPEG', 'mode': 'RGB', 'size': (4032, 3024), 'width': 4032, 'height': 3024, 'file_size_kb': 5124.71}

Step 3 — Resize to 1920 pixels wide (preserving aspect ratio).

When you specify only the width, the height is calculated automatically to preserve proportions.

python3 main.py resize ~/Pictures/vacation-photo.jpg ~/Pictures/vacation-1920.jpg 1920

Output:

✅ Success: {'success': True, 'original_size': (4032, 3024), 'new_size': (1920, 1440), 'output': '/home/user/Pictures/vacation-1920.jpg'}

Step 4 — Verify the result.

python3 main.py info ~/Pictures/vacation-1920.jpg

✅ Success: {'success': True, 'filename': 'vacation-1920.jpg', 'format': 'JPEG', 'mode': 'RGB', 'size': (1920, 1440), 'width': 1920, 'height': 1440, 'file_size_kb': 847.32}

Result: A 847 KB version of your 5 MB photo — small enough to email or post online.

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2. How to Compress an Image for Web or Email

What this does: Reduces an image's file size by saving at a lower JPEG quality. The dimensions stay the same; only the quality (and therefore file size) changes.

When to use it: An image is too large to email (many email clients limit attachments to 10–25 MB), or your website images are loading slowly.

Steps

Step 1 — Navigate to the skill directory.

cd ~/smfworks-skills/skills/image-resizer

Step 2 — Check the original file size.

python3 main.py info ~/Pictures/product-shot.jpg

Output:

✅ Success: {'success': True, 'filename': 'product-shot.jpg', 'format': 'JPEG', 'mode': 'RGB', 'size': (2400, 1600), 'width': 2400, 'height': 1600, 'file_size_kb': 3847.23}

Step 3 — Compress with default quality (85).

python3 main.py compress ~/Pictures/product-shot.jpg ~/Pictures/product-web.jpg

Output:

✅ Success: {'success': True, 'original_size_kb': 3847.23, 'new_size_kb': 847.18, 'reduction_percent': 77.98, 'output': '/home/user/Pictures/product-web.jpg'}

Step 4 — If you need even smaller, use a lower quality.

Quality 75 gives a good balance between size and appearance for most photos:

python3 main.py compress ~/Pictures/product-shot.jpg ~/Pictures/product-small.jpg 75

Step 5 — Check the result.

python3 main.py info ~/Pictures/product-small.jpg

Result: A compressed image at ~/Pictures/product-small.jpg significantly smaller than the original. Quality 85 is generally undetectable to the naked eye.

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3. How to Convert an Image to a Different Format

What this does: Saves an image in a new format (JPG, PNG, WebP, BMP, etc.) based on the output filename's extension.

When to use it: A platform requires PNG but you have JPEG. Or you want WebP for better web compression.

Steps

Step 1 — Navigate to the skill directory.

cd ~/smfworks-skills/skills/image-resizer

Step 2 — Convert PNG to JPEG.

python3 main.py convert ~/Pictures/screenshot.png ~/Pictures/screenshot.jpg

Output:

✅ Success: {'success': True, 'input_format': '.png', 'output_format': '.jpg', 'output': '/home/user/Pictures/screenshot.jpg'}

Step 3 — Convert JPEG to WebP (smaller for web).

python3 main.py convert ~/Pictures/hero.jpg ~/Pictures/hero.webp

Step 4 — Convert JPEG to PNG (lossless, if you need transparency).

python3 main.py convert ~/Pictures/photo.jpg ~/Pictures/photo.png

Result: The image is saved in the new format. The original is unchanged.

Important note about transparency: PNG supports transparency; JPEG does not. Converting a PNG with a transparent background to JPEG replaces the transparent areas with white.

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4. How to Batch Resize All Images in a Folder

What this does: Resizes every image in a source folder to the same target width and saves the results to a destination folder. Each image's height is calculated proportionally.

When to use it: You have a folder of product photos, blog images, or event photos and need all of them at a consistent width for a website or gallery.

Steps

Step 1 — Navigate to the skill directory.

cd ~/smfworks-skills/skills/image-resizer

Step 2 — Check how many images are in the folder.

ls ~/Photos/product-originals/ | wc -l

The skill handles up to 100 images per batch.

Step 3 — Create the output directory.

mkdir -p ~/Photos/product-web

Step 4 — Run batch-resize.

This example resizes all images to 800px wide:

python3 main.py batch-resize ~/Photos/product-originals ~/Photos/product-web 800

Output:

✅ Success: {'success': True, 'processed': 34, 'total': 34, 'errors': 0, 'error_details': []}

Step 5 — Verify one of the output images.

python3 main.py info ~/Photos/product-web/product-001.jpg

✅ Success: {'success': True, 'filename': 'product-001.jpg', 'format': 'JPEG', 'mode': 'RGB', 'size': (800, 600), 'width': 800, 'height': 600, 'file_size_kb': 124.83}

Result: All 34 images in ~/Photos/product-web are now 800px wide with proportional heights.

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5. How to Inspect an Image's Dimensions and Details

What this does: Prints an image's filename, format, color mode, pixel dimensions, and file size.

When to use it: Before uploading an image to a platform with specific requirements. Or to check whether an image file is valid.

Steps

Step 1 — Navigate to the skill directory.

cd ~/smfworks-skills/skills/image-resizer

Step 2 — Run the info command.

python3 main.py info ~/Downloads/logo.png

Output:

✅ Success: {'success': True, 'filename': 'logo.png', 'format': 'PNG', 'mode': 'RGBA', 'size': (512, 512), 'width': 512, 'height': 512, 'file_size_kb': 47.83}

Step 3 — Interpret the mode.

Mode	Meaning
RGB	Standard color (no transparency)
RGBA	Color with transparency (alpha channel)
L	Grayscale
P	Palette (indexed color, often GIFs)

Result: You have the exact dimensions and format — no need to open an image viewer.

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6. Automating with Cron

Schedule batch resizing to run automatically — for example, processing a new-photos folder every night.

Open the cron editor

crontab -e

Example: Batch resize new product photos every night at 11 PM

0 23 * * * python3 /home/yourname/smfworks-skills/skills/image-resizer/main.py batch-resize /home/yourname/Photos/incoming /home/yourname/Photos/web-ready 1200 >> /home/yourname/logs/image-resizer.log 2>&1

Example: Compress a daily screenshot for sharing

0 9 * * * python3 /home/yourname/smfworks-skills/skills/image-resizer/main.py compress /home/yourname/Screenshots/daily.png /home/yourname/Screenshots/daily-compressed.jpg 80 >> /home/yourname/logs/image-resizer.log 2>&1

Cron Expression Reference

Expression	Meaning
0 23 * * *	Every day at 11 PM
0 9 * * *	Every day at 9 AM
0 22 * * 0	Every Sunday at 10 PM

Create the log directory

mkdir -p ~/logs

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7. Combining with Other Skills

Image Resizer + File Organizer: Resize product images, then organize them by date:

python3 ~/smfworks-skills/skills/image-resizer/main.py batch-resize ~/Photos/raw ~/Photos/web 1200
python3 ~/smfworks-skills/skills/file-organizer/main.py organize-date ~/Photos/web

Image Resizer + QR Generator: Create a QR code, check its dimensions, then resize for print:

python3 ~/smfworks-skills/skills/qr-generator/main.py url https://mysite.com ~/Desktop/qr.png
python3 ~/smfworks-skills/skills/image-resizer/main.py resize ~/Desktop/qr.png ~/Desktop/qr-print.png 600

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8. Troubleshooting Common Issues

Pillow not installed. Run: pip install Pillow

Fix: pip install Pillow

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Unsupported file type: .heic

HEIC (iPhone) format is not supported.
Fix: Convert to JPEG first: on macOS, use Preview (Export as JPEG), or brew install imagemagick && convert photo.heic photo.jpg

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File too large: X bytes (max: 104857600)

Input file exceeds 100 MB.
Fix: Use ImageMagick for files over 100 MB: convert large-input.tif output.jpg

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Too many files (142). Max: 100

More than 100 images in the batch source directory.
Fix: Split the directory into subfolders of 100 files or fewer.

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Invalid width: 12000. Must be between 1 and 10000

Width exceeds the 10,000-pixel maximum.
Fix: Use 10,000 or less.

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Output image looks blurry

You're resizing to a much smaller dimension with a large source image. This is normal.
Tip: For photos going to print, keep them at 300 DPI. For web, 72–96 DPI (150–300px/inch equivalent) is sufficient.

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9. Tips & Best Practices

Never overwrite your originals. Always specify a different output filename. Once you overwrite an original, the higher-quality version is gone permanently.

For web images, 1200–1920px wide is usually enough. Most monitors and screens don't display images wider than 1920px. Going wider just wastes bandwidth.

Quality 85 is the sweet spot for JPEG compression. Below 70, compression artifacts become visible to most users. Quality 85 looks identical to the original in most cases and saves 50–80% of file size.

Use WebP for web pages when possible. WebP produces smaller files than JPEG or PNG with equivalent quality. Modern browsers (Chrome, Firefox, Safari, Edge) all support it.

Check info before batch resize. Run info on a sample file from the folder to understand what you're working with before batch processing 100 files.

For profile photos and avatars, check the platform's required size before resizing. Twitter wants 400×400, LinkedIn wants 400×400, Facebook wants 180×180. Resize to the exact required size to avoid platform-side resizing which can reduce quality.

Use batch-resize for consistent widths, not consistent file sizes. If you need all images under a certain file size, use a shell loop with compress instead.