png2icons

png2icons

png2icons generates Apple ICNS and Microsoft ICO files from PNG files.

This Node.js module is platform independent and has no module or native dependencies, it works on both Apple and Microsoft systems (and probably other Node.js platforms). A command line interface and an API are provided. Standalone Node.js v12.2.0 x64 executabes created with pkg can be found in the releases section.

The ideal input is a 24 bit PNG with an alpha channel (RGBA) with 1024×1024 pixels but any other dimensions and most other PNG formats do also work. If you only need to create ICO files 256×256 pixels are sufficient. It's also possible to create icon files from non-quadratic source PNGs.

Technical notes

Apple ICNS

The module is one of the few which creates a complete list of icons from 16x16 up to 512x512@2 resolutions. Many other modules omit the 16x16 and 32x32 resolution or use compression modes which are not supported on older Apple operating systems. The generated ICNS files have been tested on OS X/macOS versions from 10.10 up to 10.14 on both retina and non-retina displays. It's well possible that the generated files would also work on much older versions.

Microsoft ICO

png2icons creates ICO files with the sizes 16, 24, 32, 48, 64, 72, 96, 128 and 256 pixels (width and height). Icons can be stored as Windows bitmaps or PNGs, additionally there is a special variant where a mix of Windows bitmaps and PNGs is used. Storing as Windows bitmaps is best for compatibility reasons but the file size is quite large.

PNG in most cases produces much smaller file sizes but the generated ICO file can cause display problems in Windows version older than Windows 10. In general the files show up without problems in Windows Explorer at any size and at any resolution. This is true for Windows versions down to Windows 7 (older not tested), but the file properties dialog of older Windows versions may show a scrambled view of the embedded icon. Windows 10 does not have this problem.

If the ICO file should be used as the embedded icon in a Windows executable the command line switch -icowe (or -allwe, see below) can be used. If used, png2icons will write all icons smaller than 64x64 pixels in Windows bitmap format to the output file and the rest in PNG format. This helps to reduce the icon storage size in the executable and seems to work well in all Windows versions. It has been tested in Windows 7 up to Windows 10 at all kinds of screen resolutions (normal and HiDPI) and also at all different magnification levels.

Command line usage

png2icons infile outfile format [-nn | - bl | -bc | -bz | -hm | -bc2] [-i]

Don't append a file extension to outfile, it will be set automatically.

You have to set format to one of the following values:

Value	Output
-icns	Apple ICNS format, creates <outfile>.icns
-ico	Microsoft ICO format, creates <outfile>.ico (contained icons as BMP)
-icop	Microsoft ICO format, creates <outfile>.ico (contained icons as PNG)
-icowe	Microsoft ICO format, creates <outfile>.ico (for Windows executables, see technical notes)
-all	Create both ICNS and ICO format (ICO with BMP)
-allp	Create both ICNS and ICO format (ICO with PNG)
-allwe	Create both ICNS and ICO format (ICO for Windows executables, see technical notes)

You can optionally set the interpolation algorithm to one of the following parameters:

Parameter	Interpolation algorithm
-nn	Nearest Neighbor, fastest, mediocre to OK quality
-bl	Bilinear, fast, quality OK
-bc	Bicubic, slower, good to very good quality
-bz	Bezier, quite slow, high quality
-hm	Hermite, quite slow, high quality
-bc2	Bicubic alternative, fast, good to very good quality (not thoroughly tested)

If no interpolation is set Bicubic (-bc) is used as the default.

With -i info messages are printed to the console during processing.

Example:

png2icons sample.png icon -allp -bc -i

This will create the files icon.icns and icon.ico where icon.ico contains icons in PNG format. During processing info messages will be printed to the console.

API usage

The module exports four functions:

function createICNS(input, scalingAlgorithm, numOfColors)
function createICO(input, scalingAlgorithm, numOfColors, usePNG, forWinExe)
function setLogger(logFn)
function clearCache()

createICNS creates the Apple ICNS format, createICO creates the Microsoft ICO format.

Parameters identical for both create* functions:

• input is a buffer containing the raw content of a PNG file, obtained, for example, with fs.readFileSync.

• scalingAlgorithm sets the algorithm to be used when scaling the input images for the various icon sizes. It can be one of the following constants:

  RESIZE_NEAREST_NEIGHBOR = 0;
  RESIZE_BILINEAR = 1;
  RESIZE_BICUBIC = 2;
  RESIZE_BEZIER = 3;
  RESIZE_HERMITE = 4;
  RESIZE_BICUBIC2 = 5;
  

• numOfColors controls the reduction of colors in the compressed output if PNG is used for the icons . A value of 0 retains all colors from input (lossless), a value greater than 0 reduces the colors to the given number (per color channel, so 256 is the maximum value). This can lead to much smaller files. Please note: numOfColors is ignored if usePNG is set to false (createICO) but it is always used if forWinExe is true.

If the boolean parameter usePNG for createICO is set to true this function will use PNG for each icon in the created ICO file, otherwise Windows bitmaps will be used. Please note that PNG in ICO files may lead to problems in Windows versions older than Vista.

If the optional parameter forWinExe for createICO is set to true png2icons will create a mix of PNG and BMP icons in the generated output. The icon sizes 16, 24, 32 and 48 will be in BMP format and all others in PNG format. This helps to reduce the ICO file size. Using BMP for the smaller icon sizes prevents display problems in the file properties dialog of Windows versions older than Windows 10. This parameter should be used, if an ICO file for embedding in Windows executables must be created (for example for Electron apps).

With setLogger you can supply your own logging function. The logging function (logFn) must accept the same parameters like console.log, so you could use that in simple cases, e. g. setLogger(console.log). No logging function is set by default.

clearCache: png2icons tries to cache as much image data as possible to speed up processing. If, for example, the same input image is used to create multiple different output formats it reuses already scaled images. clearCache frees all internally cached image data .

The return value is null in case of an error, otherwise a buffer which contains the binary data of the generated ICNS/ICO file is returned. You could use, for example, fs.writeFileSync to save it as a file.

Example:

var png2icons = require("png2icons");
var fs = require("fs");

var input = fs.readFileSync("sample.png");

// Apple ICNS with bilinear interpolation and no color reduction.
// Log infos via console.log.
png2icons.setLogger(console.log);
var output = png2icons.createICNS(input, png2icons.BILINEAR, 0);
if (output) {
    fs.writeFileSync("icon.icns", output);
}

// Microsoft ICO using PNG icons with Bezier interpolation and
// reduction to 20 colors.
// Log infos via console.log (logging function already set before).
output = png2icons.createICO(input, png2icons.BEZIER, 20, true);
fs.writeFileSync("icon_png.ico", output);

// Microsoft ICO using BMP icons with Hermite interpolation,
// (numOfColors is ignored). Turn off any logging again.
png2icons.setLogger(null);
output = png2icons.createICO(input, png2icons.HERMITE, 0, false);
fs.writeFileSync("icon_bmp.ico", output);

// Microsoft ICO using PNG and BMP icons with alternative bicubic
// interpolation, (numOfColors applies!). Suitable for embedding
// the icon file in Windows executables. Logging is already off.
output = png2icons.createICO(input, png2icons.BICUBIC2, 0, false, true);
fs.writeFileSync("icon_winexe.ico", output);

Development

After cloning the repository run npm i or npm install to install the necessary dependencies. A run of npm run make creates the JavaScript output files. npm run lint checks the TypeScript sources with a linter. npm test converts the sample PNG file in ./sample to both the ICNS and ICO (for Windows executables) format (./sample/sample.icns and ./sample/sample.ico will be generated).

png2icons is developed in TypeScript. If you're using TypeScript make sure that you add @types/node to the development dependencies in your package.json, otherwise the compiler will complain about missing definitions.

Credits

This module wouldn't have been possible without code from the following projects:

• Read/write PNG images: UPNG.js
• Image blitting: Jimp
• Image resizing: ImageJS
• PackBits compression: packbits
• Fast bicubic interpolation: Reddit user imbcmdth; JSFiddle
• ZIP handling: UZIP.js

License

MIT © idesis GmbH, Rellinghauser Straße 334F, D-45136 Essen

See the LICENSE file for details.

Changelog

2.0.1

• Fixed image caching bug which used the first given input forever on all subsequent API calls.
• Added exported function clearCache().

2.0.0

• Added sizes is32and il32 to ICNS.
• Added special ICO format for Windows executables.
• Noticeably faster rescaling due to inlining interpolate functions.
• Much faster ICNS generation due to caching of icon chunks with the same size.
• Added much faster alternative bicubic rescaling (should work although not thoroughly tested).
• Prevent color palette in small PNGs (caused scrambled display of small icons under some conditions).
• Fixed Windows DIB creation for ICO (caused scrambled display of small icons under some conditions).
• Fixed wrong offsets/sizes for PNGs in ICO.
• Fixed non-quadratic images in ICNS.
• Removed dependcy from pako.
• Add missing TypeScript definition files.
• Use ES2015 (TypeScript).