Count colors in image: `NSCountedSet` and `colorAtX` are very slow

Question

I\'m making an OS X app which creates a color scheme from the main colors of an image.

As a first step, I\'m using NSCountedSet and colorAtX to

Answer 1

The fastest alternative to colorAtX() would be iterating over the raw bytes of the image using let bitmapBytes = imageRep.bitmapData and composing the colour yourself from that information, which should be really simple if it's just RGBA data. Instead of your for x/y loop, do something like this...

let bitmapBytes = imageRep.bitmapData
var colors = Dictionary<UInt32, Int>()

var index = 0
for _ in 0..<(width * height) {
    let r = UInt32(bitmapBytes[index++])
    let g = UInt32(bitmapBytes[index++])
    let b = UInt32(bitmapBytes[index++])
    let a = UInt32(bitmapBytes[index++])
    let finalColor = (r << 24) + (g << 16) + (b << 8) + a   

    if colors[finalColor] == nil {
        colors[finalColor] = 1
    } else {
        colors[finalColor]!++
    }
}

You will have to check the order of the RGBA values though, I just guessed!

The quickest way to maintain a count might just be a [Int, Int] dictionary of pixel values to counts, doing something like colors[color]++. Later on if you need to you can convert that to a NSColor using NSColor(calibratedRed red: CGFloat, green green: CGFloat, blue blue: CGFloat, alpha alpha: CGFloat)