How can I make this Bitmap gamma function in Android run faster?

Question

I have written the following function to change the gamma of a Bitmap, but it's kind of slow, even on small (300 by 300) bitmaps. How can I make this function run faster? For example, is there a better way (i.e., faster way) to access individual pixel values from a Bitmap?

public Bitmap apply(Bitmap bmp, float gamma) {
    if (bmp == null)
        return null;

    int width = bmp.getWidth();
    int height = bmp.getHeight();

    int[] pixels = new int[width * height];
    bmp.getPixels(pixels, 0, width, 0, 0, width, height);

    int[] powers = new int[256];
    for (int i = 0; i < powers.length; i++)
        powers[i] = (int)(Math.pow(i / 255.0f, 1.0f / gamma) * 255);

    for (int p = 0; p < pixels.length; p++) {
        int r = Color.red(pixels[p]);
        int g = Color.green(pixels[p]);
        int b = Color.blue(pixels[p]);
        int newR = powers[r];
        int newG = powers[g];
        int newB = powers[b];
        pixels[p] = Color.rgb(newR, newG, newB);
    }

    Bitmap newBmp = Bitmap.createBitmap(pixels, 0, width, width, height, Config.ARGB_8888);
    return newBmp;
}

As an optimization, I calculate the powers ahead of time on all possible pixel values (0 to 255), which helps, but it's not enough. Also, declaring all the int's outside of the second for loop didn't help much, so I left them in. Thanks in advance.

Answer 1

I would look into using OpenGL or RenderScript for that if you really want it to be fast. Both have nice integration on Android.