n0m4dz / UPNG.js

Fast and advanced PNG decoder

UPNG.js

A small, fast and advanced PNG decoder. It is the main PNG decoder for Photopea image editor.

• Supports all color types (including Grayscale and Palettes)
• Supports all channel depths (1, 2, 4, 8, 16)
• Supports interlaced images
• Opens PNGs which other libraries can not open (tested with PngSuite)

UPNG.decode(buffer)

• buffer: ArrayBuffer containing the PNG file
• returns an image object with following properties:
• • width: the width of the image
• • height: the height of the image
• • depth: number of bits per channel
• • ctype: color type of the file (Truecolor, Grayscale, Palette ...)
• • tabs: additional chunks of the PNG file
• • data: pixel data of the image

PNG files may have different number of channels and different color depth. The interpretation of data depends on the current color type and color depth (see the PNG specification).

UPNG.toRGBA8(img)

• img: PNG image object (returned by UPNG.decode())
• returns Uint8Array of the image in RGBA format, 8 bits per channel (ready to use in ctx.putImageData() etc.)

PNG format uses the Inflate algorithm. Right now, UPNG.js calls Pako.js library for the Inflate method. To remove this dependency, rewrite UPNG.decode._inflate() method.