Published on 2026-03-01 18:37 by Manu Gallego

imgtools.sh

A command-line utility to optimize, resize, and convert images for the web using ImageMagick (v6/v7) and dedicated encoders (mozjpeg, cwebp, avifenc) when available.

Features

Quality-based optimization (optimize <0-100>).
Aspect ratio-preserving resize (resize <size>).
Combined resize + optimize in a single run.
Format conversion (jpg, png, webp, avif).
Progressive JPEG / interlaced PNG (--progressive).
Parallel processing (--jobs N) for large batches.
Watch mode (--watch): processes new files as they land in the input directory.
Recursive processing of subdirectories.
Simulation mode (--dry-run) without writing files.
Prefix/suffix support for output filenames.
Auto-selects the best available encoder per format.
Final summary with processing stats and savings.

Requirements

sh (POSIX-compatible script).
ImageMagick:
- v7: magick
- or v6: convert

Better encoders (optional, auto-detected)

When installed, these replace ImageMagick for their respective formats and produce smaller files at equal quality:

Encoder	Format	Install
`mozjpeg`	JPEG	`brew install mozjpeg`
`cwebp`	WebP	`brew install webp`
`avifenc`	AVIF	`brew install libavif`
`fswatch` / `inotifywait`	(watch mode)	`brew install fswatch`

Dependency installation

The script includes a command to check and install dependencies:

./imgtools.sh install

It detects and attempts installation via apt, brew, dnf, yum, or apk.

Usage

./imgtools.sh [action] [value] [options]

Actions

optimize <0-100>: compresses using a quality percentage.
resize <size>: resizes while preserving aspect ratio.
- 1200h → max width 1200px
- 400v → max height 400px
- 1200 → equivalent to 1200h
install: checks and installs dependencies.

Options

-i, --input <dir>: input directory (default: current directory).
-o, --output <dir>: output directory (default: same as input).
-v, --verbose: shows per-file details and savings.
-r, --recursive: processes subdirectories.
-j, --jobs <n>: parallel workers (default: 1).
--progressive: write progressive JPEG / interlaced PNG.
--watch: monitor input directory; process new files as they arrive.
--overwrite: overwrites existing output files.
--dry-run: simulates execution, writes nothing.
--suffix <txt>: appends _<txt> to each output filename (e.g. --suffix web → photo_web.jpg).
--prefix <txt>: prepends <txt>_ to each output filename (e.g. --prefix web → web_photo.jpg).
--format <fmt>: output format (jpg | png | webp | avif).
--ext <list>: comma-separated extensions to scan (default: jpg,jpeg,png,gif,bmp,tiff,webp).
--optimize <0-100>: also optimizes when main action is resize.
--resize <size>: also resizes when main action is optimize.
-h, --help: shows help.

Examples

Optimize images at 80% quality:

./imgtools.sh optimize 80

Optimize and also resize/convert to WebP:

./imgtools.sh optimize 85 --resize 1200h --format webp

Resize from src to dist with suffix and verbose output:

./imgtools.sh resize 1200h -i ./src -o ./dist --suffix web -v

Optimize with progressive JPEG using 4 parallel workers:

./imgtools.sh optimize 80 --progressive --jobs 4 -i ./src -o ./dist

Process recursively and overwrite outputs:

./imgtools.sh resize 400v --overwrite --recursive

Watch a directory and convert every new upload to WebP on the fly:

./imgtools.sh optimize 80 --format webp --watch -i ./uploads -o ./dist

Simulate without writing files:

./imgtools.sh optimize 80 --prefix web --format webp --dry-run -v

Recommended workflow

Run in simulation mode to validate outputs:
```
./imgtools.sh optimize 80 --dry-run -v
```
Run again without --dry-run.
Review the final summary (processed, skipped, errors, and total savings).

Project structure

img_tools/
├── imgtools.sh
└── README.md

Notes

ICC color profiles are preserved during optimize: the script converts to sRGB before stripping metadata, so color rendering stays correct in browsers.
--ext filters which files are picked up from the input directory.
If the output directory does not exist, it is created automatically (except in --dry-run).
In --jobs N mode, stats (processed, saved bytes, errors) are aggregated correctly across all workers.
AVIF falls back to ImageMagick with libheif if avifenc is not installed.