ICNS Icon Creation for macOS Apps: Format Analysis and Resolution Guide
This article explains the characteristics of the ICNS container format, organizes the corresponding rules for 7 standard resolution levels, describes the requirements for source image preparation, and helps developers generate standard-compliant macOS icon files.
Zaktualizowano 2026-08-11
Similarities and differences between ICNS and Windows ICO formats
ICNS is an icon container format exclusive to macOS, while ICO is the corresponding icon container format for the Windows platform. Both formats support embedding multiple icon entries of different resolutions in a single file to meet the needs of different display scenarios.
The core differences between the two formats lie in the applicable operating systems and entry type definitions. ICNS follows the resolution entry specification specified by Apple, while ICO adapts to the display scaling logic of Windows systems. The two formats cannot be used directly across systems.
Correspondence between 7 standard ICNS resolutions and Retina displays
An ICNS container needs to include 7 resolution levels, with entry names ranging from icp4 to ic10, covering the pixel range from 16×16 to 1024×1024, to meet the display requirements of all macOS scenarios from the menu bar to Launchpad.
All entries larger than the base size correspond to the @2x scaling scenario for Retina screens. macOS automatically selects and renders the icon entry with the matching resolution according to the current display device type to ensure clear display.
| ICNS entry identifier | Actual pixel size | Corresponding Retina@2x scenario |
|---|---|---|
| icp4 | 16×16 | Non-Retina 8×8pt icon |
| icp5 | 32×32 | Non-Retina 16×16pt / Retina 8×8pt |
| icp6 | 64×64 | Retina 16×16pt |
| ic07 | 128×128 | Non-Retina 128×128pt |
| ic08 | 256×256 | Non-Retina 256×256pt / Retina 128×128pt |
| ic09 | 512×512 | Retina 256×256pt |
| ic10 | 1024×1024 | Retina 512×512pt |
Requirements for source image preparation for ICNS generation
To generate an ICNS file, developers need to prepare a 1024×1024 pixel source image in PNG format. Tools can scale this source image to generate the corresponding 7 resolution icon entries, eliminating the need for developers to manually output all sizes.
The source image must use a transparent background to adapt to the icon display effect of macOS Dock and Finder. Icons with solid-color backgrounds will display extra color blocks in the system UI, which does not comply with Apple's design specifications.
Scenario for reverse unpacking of ICNS to extract PNG
Some developers have finished packaging their applications but lost the original design source files, only retaining the compiled ICNS icon file. In this case, an ICNS to PNG converter can be used for reverse unpacking to extract all resolution icons embedded in the container.
By default, the extraction operation selects the maximum size entry of 1024×1024 pixels. This size is sufficient to support secondary modification of most new application icons, and can also meet the generation requirements of new specification ICNS after scaling.
Częste pytania
Can a PNG smaller than 1024×1024 generate a qualified ICNS?
It can generate an ICNS, but the highest resolution entry cannot reach the 1024×1024 specification, which will result in stretching and blurring in the Retina 512pt scenario, and does not meet Apple's packaging review requirements.
Do custom folder icons also require the ICNS format?
macOS Finder supports directly using PNG to set folder icons, but using ICNS can adapt to different display sizes, ensure clear display in all scenarios, and provide more stable adaptation effect.
Can ICNS to PNG tools extract all embedded resolutions?
ICNS to PNG tools support extracting all embedded resolution entries from the container, and also support extracting only the maximum size entry. Specific functions are subject to the current public rules of the tool.