Apple-ICNS

Apple Icon Image

image/x-icns Released 2001 · by Apple Inc.

The image/x-icns MIME type represents the Apple Icon Image format (ICNS), the native icon format used by macOS (formerly Mac OS X). An ICNS file acts as a container that bundles multiple resolutions and color depths of an icon into a single file, ensuring applications look sharp on everything from legacy standard-definition displays to modern high-density Retina screens (ranging from 16x16 to 1024x1024 pixels). While early versions stored uncompressed raw pixel data with separate 8-bit alpha masks, modern macOS versions encapsulate standard PNG or JPEG 2000 streams within the ICNS chunks for higher resolutions.

Icons & UI Transparency Production Ready

Technical Specifications

MIME Type

image/x-icns

Extensions

.icns

Container

Chunk-based (OSType Header)

Compression

Uncompressed (Legacy) & PNG (Modern) & JPEG 2000 (Modern)

Algorithms

NoneDeflate (via embedded PNG)Wavelet (via embedded JP2)

Color Depth

1-bit (Monochrome), 4-bit, 8-bit, 24-bit (RGB), 32-bit (RGBA)

Metadata

ICC

Capabilities

Transparency

Animation

Progressive Loading

Alpha Channel

HDR Support

Official Specification

Aliases: image/icnsimage/mac-icns

Magic Bytes & HTTP Headers

File Signature (Magic Bytes)

69 63 6E 73

ASCII: icns

HTTP Headers

Content-Type: image/x-icns

Content-Type: image/icns

HTML Accept Attribute

accept="image/x-icns, .icns"

Browser Support Matrix

Browser	Status	Min Version
Chrome	Not Supported	—
Firefox	Not Supported	—
Safari	Not Supported	—
Edge	Not Supported	—
Internet Explorer	Not Supported	Legacy

Advantages & Limitations

Advantages

Seamlessly handles multi-resolution scaling on macOS, perfectly serving both standard and high-DPI (Retina) displays from a single asset
Modern versions efficiently embed standard PNG files, making it much easier to parse the high-resolution layers than the legacy raw pixel formats

Limitations

Strictly bound to the Apple ecosystem; completely useless natively on Windows, Linux, or the Web
The internal chunking structure is notoriously messy, utilizing dozens of different undocumented, legacy OSType tags spanning 20+ years of Apple history

Developer Code Snippets

import magic
# Libmagic natively detects the 'icns' magic byte signature
print(magic.from_file('app_icon.icns', mime=True)) # Outputs 'image/x-icns'

const fs = require('fs');
// Manually detecting the 'icns' magic bytes
const buffer = Buffer.alloc(4);
const fd = fs.openSync('app_icon.icns', 'r');
fs.readSync(fd, buffer, 0, 4, 0);
fs.closeSync(fd);
const isICNS = buffer.toString('ascii') === 'icns';
console.log('Is Apple ICNS:', isICNS);

import (
    "bytes"
    "net/http"
)
// Custom check for the ICNS Magic Bytes
// isICNS := bytes.HasPrefix(buf, []byte("icns"))

$mime = mime_content_type('app_icon.icns');
echo $mime; // Standard setups will often resolve this to 'image/x-icns' or 'image/icns'

File Detection Steps

How to programmatically detect a image/x-icns file by reading its raw bytes:

1 Check the first 4 bytes for the ASCII string 'icns' (Hex: 69 63 6E 73).
2 The next 4 bytes form a 32-bit big-endian integer representing the total file size in bytes.
3 The rest of the file consists of data chunks, each starting with a 4-byte OSType identifier (e.g., 'ic08' for a 256x256 icon) and a 4-byte chunk length.

Software Support

A

Apple Preview

X

Xcode (iconutil)

ImageMagick

GIMP

Conversion Tools

Share & Embed

Markdown Badge

[![Apple-ICNS Format](https://freewebptojpg.com/mime/image/apple-icns/badge.svg)](https://freewebptojpg.com/mime/image/apple-icns)

Interactive iframe Widget

<iframe src="https://freewebptojpg.com/mime/image/apple-icns/embed" width="100%" height="280" style="border:1px solid #cbd5e1;border-radius:8px;" title="Apple-ICNS Specs"></iframe>

JSON API

All data on this page is available as a free, open JSON API. Use it in your project, documentation, or tooling.

GET https://freewebptojpg.com/mime/image/apple-icns.json Open JSON

Free to use

No auth required

CORS enabled

Use from any domain

Cached 24h

Cache-Control headers set

Frequently Asked Questions

What is an ICNS file?

An ICNS file is the standard icon format used by Apple's macOS. It stores multiple sizes of an icon inside a single file so the operating system can seamlessly switch to the appropriate resolution depending on the display (e.g., standard vs. Retina) or context (e.g., Finder vs. Dock).

How do I create an ICNS file?

Developers typically create ICNS files using Apple's Xcode via an '.iconset' folder, or through command-line utilities like 'iconutil' on macOS. There are also third-party tools and web converters that can compile a set of PNGs into an ICNS file for Windows or Linux users.

Can I use an ICNS file as a favicon on a website?

No. Web browsers do not natively support the ICNS format. You must convert it to an ICO, PNG, or SVG file to use it as a website favicon.