ImageCRC

Bulk image optimization and format conversion for macOS.

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Drop a folder of images, pick a format and quality, hit Start. ImageCRC fans the work out across every CPU core, shows a smooth progress overlay, and opens the output folder in Finder when it's done. Everything runs locally — no uploads, no telemetry.

Features

• Input: JPG · JPEG · PNG · SVG · WebP · AVIF · HEIC
• Output: JPG · PNG · WebP · AVIF
• Quality slider (0–100%) with format-aware semantics — JPEG/AVIF/WebP scale linearly, PNG goes lossless at 100% and is quantized via pngquant below
• Optional resize (Fit / Fill with centered crop) before encoding; never upscales unless asked
• Parallel conversion bounded by activeProcessorCount, cancellable mid-run
• Light / Dark / System appearance toggle with animated transition

Requirements

• macOS 14 Sonoma or newer (AVIF encoding requires 14+).
• Xcode 15.3+ or Command Line Tools for Xcode 15.3+ — provides the Swift 5.10 toolchain. Verify with swift --version. If missing: xcode-select --install.
• Homebrew — used to install pngquant below.
• pngquant — brew install pngquant. Required for PNG output at quality < 100 (the lossless ImageIO bytes are piped through pngquant for indexed-color quantization). Scripts/make-app.sh looks it up via brew --prefix pngquant and bundles the binary into Contents/Resources/bin/ of the .app. Without it, swift build still succeeds, but make-app.sh prints a warning and PNG conversion below 100% quality will fail at runtime.

SwiftPM dependencies (libwebp via SDWebImage/libwebp-Xcode) resolve automatically on the first swift build — no manual install needed.

Optional

• XcodeGen — brew install xcodegen. Only needed if you want to regenerate ImageCRC.xcodeproj from project.yml (xcodegen generate). The SwiftPM build (make-app.sh) does not use Xcode.

All other tools used by the build/packaging scripts (codesign, sips, iconutil, hdiutil, /usr/libexec/PlistBuddy) ship with macOS / the Xcode CLI tools.

Build & run

./Scripts/make-app.sh
open ./ImageCRC.app

The script runs swift build -c release, assembles a .app bundle with an ad-hoc signature, and leaves it at ./ImageCRC.app. Set CONFIG=debug for a debug build.

Packaging

./Scripts/make-dmg.sh    # → ImageCRC-<version>.dmg
./Scripts/make-icon.sh   # regenerate Resources/AppIcon.icns from the 1024×1024 master

Stack

• Swift + SwiftUI — single-window app, @Observable state, no AppKit shell.
• ImageIO for JPG / PNG / HEIC / AVIF · libwebp (via SDWebImage/libwebp-Xcode) for WebP · NSImage for SVG rasterization · pngquant subprocess for PNG lossy.
• TaskGroup-based parallel pipeline bounded by CPU count, cooperative cancellation between decode → resize → encode → write.
• MVVM split — ConversionViewModel is the only bridge between the UI and an AsyncStream<ConversionEvent> driven by ImageConverter.

See CLAUDE.md for the full architecture map.

Design docs

• Original design — quality semantics, concurrency model
• Resize feature
• Dark theme

Distribution note

pngquant is bundled into the .app and is licensed under GPL v3, so any redistributed binary is a combined GPL v3 work — and therefore not eligible for the Mac App Store.