Get an array of pixels from an NSImage and use this array to render the image. Handy for performing per-pixel operations on an image

reRender.swift

import Cocoa

// Representation of a pixel
struct Pixel {
    var a: UInt8
    var r: UInt8
    var g: UInt8
    var b: UInt8
}

// Get pixels from an NSImage
func imageToPixels(image: NSImage) -> [Pixel] {
    var returnPixels = [Pixel]()

    let image = NSImage(named: "uv")!

    let pixelData = (image.cgImage(forProposedRect: nil, context: nil, hints: nil)!).dataProvider!.data
    let data: UnsafePointer<UInt8> = CFDataGetBytePtr(pixelData)

    for y in 0..<Int(image.size.height) {
        for x in 0..<Int(image.size.width) {
            let pos = CGPoint(x: x, y: y)

            let pixelInfo: Int = ((Int(image.size.width) * Int(pos.y) * 4) + Int(pos.x) * 4)

            let r = data[pixelInfo]
            let g = data[pixelInfo + 1]
            let b = data[pixelInfo + 2]
            let a = data[pixelInfo + 3]
            returnPixels.append(Pixel(a: a, r: r, g: g, b: b))
        }
    }
    return returnPixels
}

// Render pixels
func pixelsToImage(pixels: [Pixel], width: Int, height: Int) -> NSImage? {
    guard width > 0 && height > 0 else { return nil }
    guard pixels.count == width * height else { return nil }

    let rgbColorSpace = CGColorSpaceCreateDeviceRGB()
    let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedFirst.rawValue)
    let bitsPerComponent = 8
    let bitsPerPixel = 32

    var data = pixels
    guard let providerRef = CGDataProvider(data: NSData(bytes: &data,
                            length: data.count * MemoryLayout<Pixel>.size)
        )
        else { return nil }

    guard let cgim = CGImage(
        width: width,
        height: height,
        bitsPerComponent: bitsPerComponent,
        bitsPerPixel: bitsPerPixel,
        bytesPerRow: width * MemoryLayout<Pixel>.size,
        space: rgbColorSpace,
        bitmapInfo: bitmapInfo,
        provider: providerRef,
        decode: nil,
        shouldInterpolate: true,
        intent: .defaultIntent
        )
        else { return nil }

    return NSImage(cgImage: cgim, size: CGSize(width: width, height: height))
}

// Code to get pixels and render them again
let input = NSImage(named: "image_name")!
let pixels = imageToPixels(image: input)
let output = pixelsToImage(pixels: pixels, width: Int, height: Int)