     
     private func intensityMatrixFromPixelPointer(pointer: PixelPointer) -> [[Double]]
     {
-        let matrix = Pixel.createPixelMatrix(width, height)
+        let
+        width  = Int(image.size.width),
+        height = Int(image.size.height),
+        matrix = Pixel.createPixelMatrix(width, height)
         return matrix.map { pixelRow in
             pixelRow.map { pixel in
                 pixel.intensityFromPixelPointer(pointer)

    private func symbolFromIntensity(intensity: Double) -> String
    {
        assert(0.0 <= intensity && intensity <= 1.0)
        let
        factor = palette.symbols.count - 1,
        value  = round(intensity * Double(factor)),

{
    private let
    image:   UIImage,
    palette: AsciiPalette
    
    init(_ image: UIImage, _ palette: AsciiPalette)
    {
        self.image   = image
        self.palette = palette
    }
    
