swift-image-formats

A cross-platform Swift library for working with various image file formats.

Supported image formats

• .png: Using pnggroup/libpng (via the-swift-collective/libpng)
• .jpeg: Using tayloraswift/jpeg
• .webp: Using webmproject/libwebp (via the-swift-collective/libwebp)

In future I'd like to add support for bitmaps, gifs, and heic files.

Usage

Loading image files

There are many different ways to load images. Which one you use will depend on how much you know about the image that you're loading. In this example we will let Image use the file extension to detect the file format, but you can also just give it bytes and it will detect the image format from the first few bytes of the file. If you know the file format up-front, you can use Image.load(from:as:).

import Foundation
import ImageFormats

let url = URL(fileURLWithPath: "image.png")
let bytes = [UInt8](try Data(contentsOf: url))
let image = Image<RGBA>.load(from: bytes, usingFileExtension: fileExtension)

print("width = \(image.width)")
print("height = \(image.height)")
print("pixel @ (0, 0) = \(image[row: 0][column: 0])")

Saving image files

import Foundation
import ImageFormats

let image: Image<RGBA> = ...
let url = URL(fileURLWithPath: "image.png")

let pngBytes = try image.encodeToPNG()
try Data(pngBytes).write(to: url)

Detect file format from magic bytes

let bytes: [UInt8] = [...]
let format = Image.detectFormat(of: bytes)

Converting pixel format

let rgbaImage: Image<RGBA> = ...
let rgbImage = rgbaImage.convert(to: RGB.self)

Creating a custom pixel format

struct Grayscale: BytesConvertible, RGBAConvertible {
    static let stride = 1

    var luminosity: UInt8

    var rgba: RGBA {
        RGBA(
            luminosity,
            luminosity,
            luminosity,
            255
        )
    }

    init(_ luminosity: UInt8) {
        self.luminosity = luminosity
    }

    init(from rgba: RGBA) {
        luminosity = (rgba.red * 299 + rgba.green * 587 + rgba.blue * 114) / 1000
    }

    func encode(to array: inout [UInt8], at offset: Int) {
        array[offset] = luminosity
    }

    static func decode(_ bytes: ArraySlice<UInt8>) -> Self {
        return Self(bytes[bytes.startIndex])
    }
}

You can now convert images to grayscale from any format. All conversions go via RGBA.

let image: Image<RGB> = ...
let grayscale = image.convert(to: Grayscale.self)

Saving image files

Not yet implemented.