About

This is not merely an image resizer; it is a compliance engine for the Apple Human Interface Guidelines (HIG). In the macOS ecosystem, an application icon is not a single file but a complex directory structure (.iconset) containing up to 10 specific bitmap assets. These range from 16×16 px for the Finder sidebar to 1024×1024 px for Retina displays.

The mathematical shape of a modern macOS icon is a continuous curvature superellipse (Squircle), defined by the equation |x|⁵ + |y|⁵ = r⁵. Unlike a standard rounded rectangle, this shape has no straight lines. This tool helps developers visualize this mask before compilation, ensuring critical logo elements are not clipped. It generates the strictly named files (e.g., [email protected]) required by the iconutil binary.

Formulas

The core logic of icon asset generation relies on the transformation of the vector space R² to the raster grid. The downsampling function f maps the source image I to a target resolution d using Bicubic interpolation logic:

f(x, y) = 3∑i=0 3∑j=0 a_ij xⁱ y^j

Additionally, for the Retina assets (marked as @2x), the pixel density ρ is doubled. If the logical size is w × h, the physical raster size P is:

P = w ⋅ 200h ⋅ 2

Reference Data

Asset Name	Points (pt)	Scale Factor (s)	Pixels (px)	Visual Context
icon_16x16.png	16	1x	16×16	Finder Sidebar (Low-DPI)
[email protected]	16	2x	32×32	Finder Sidebar (Retina)
icon_32x32.png	32	1x	32×32	List View / Toolbar
[email protected]	32	2x	64×64	List View (Retina)
icon_128x128.png	128	1x	128×128	Dock (Standard)
[email protected]	128	2x	256×256	Dock (Retina)
icon_256x256.png	256	1x	256×256	Spotlight / Modal
[email protected]	256	2x	512×512	Alerts (Retina)
icon_512x512.png	512	1x	512×512	App Store (Low-DPI)
[email protected]	512	2x	1024×1024	App Store (Retina)

Frequently Asked Questions

Xcode and the `iconutil` command-line tool expect a specific folder naming convention (`.iconset` suffix) and strict internal filenames (`icon_XxX.png`). Any deviation - even a single missing pixel in dimension or a wrong underscore - will cause the compilation to fail with error `Invalid iconset`.

Since macOS Big Sur, icons are not squares with rounded corners; they are superellipses. This tool allows you to toggle a "Safe Zone" mask. You should upload a square image that bleeds to the edges. The OS applies the mask. If you pre-mask your image, you risk white slivers appearing at the corners (double-masking artifact).

The browser's Canvas API typically operates in the sRGB color space. While the generated PNGs are high quality, professional print-grade P3 profiles might be approximated to sRGB. For 99% of app development needs, this is sufficient and standard.

Partially. The internal PNGs are compatible, but iOS requires a strictly different folder structure (`.appiconset`) and a `Contents.json` manifest file. This tool is optimized specifically for the macOS `iconutil` workflow.

Downscaling (reducing size) preserves quality, while upscaling (increasing size) invents pixels that don't exist, leading to blurriness. Since the largest required asset is 1024px (for `512x512@2x`), your source must meet or exceed this to ensure crispness on 5K iMacs and Pro Display XDRs.