Function applyColorTransform

transform.go:213–259

(pixels []color.NRGBA, width, height, transBits int)

}

func applyColorTransform(pixels []color.NRGBA, width, height, transBits int) (int, int, []color.NRGBA) {
    bw := (width + (1 << transBits) - 1) >> transBits
    bh := (height + (1 << transBits) - 1) >> transBits

    blocks := make([]color.NRGBA, bw * bh)
    deltas := make([]color.NRGBA, width * height)
    
    //TODO: analyze block and pick best Color transform Element (CTE)
    cte := color.NRGBA {
        R: 1,   //red to blue
        G: 2,   //green to blue
        B: 3,   //green to red
        A: 255,
    }
    
    for y := 0; y < bh; y++ {
        for x := 0; x < bw; x++ {
            mx := min((x + 1) << transBits, width)
            my := min((y + 1) << transBits, height)

            for tx := x << transBits; tx < mx; tx++ {
                for ty := y << transBits; ty < my; ty++ {
                    off := ty * width + tx

                    r := int(int8(pixels[off].R))
                    g := int(int8(pixels[off].G))
                    b := int(int8(pixels[off].B))
                
                    b -= int(int8((int16(int8(cte.G)) * int16(g)) >> 5))
                    b -= int(int8((int16(int8(cte.R)) * int16(r)) >> 5))
                    r -= int(int8((int16(int8(cte.B)) * int16(g)) >> 5))
                    
                    pixels[off].R = uint8(r & 0xff)
                    pixels[off].B = uint8(b & 0xff)

                    deltas[off] = pixels[off]
                }
            }

            blocks[y * bw + x] = cte
        }
    }
    
    copy(pixels, deltas)
    
    return bw, bh, blocks
}

func applySubtractGreenTransform(pixels []color.NRGBA) {
    for i, _ := range pixels {