Why is my Android app so slow?

0
votes

I have an image (of size 1024x1024) in an int array (int[] pixels) and I am inverting one channel using the following loop...

int i = 0;
for (int y = 0; y < H; y++) {
    for (int x = 0; x < W; x++) {
       int color = pixels[i];
       pixels[i] = Color.argb(Color.alpha(color), 255 - Color.red(color), Color.green(color), Color.blue(color));
       i++;
    }
}

This takes more than 1 second on my new Galaxy S4 phone. Similar loop runs in a blink of an eye even on an older iPhone. Is there something I am doing wrong here?

If I replace "Color.argb(Color.alpha(color), 255 - Color.red(color), Color.green(color), Color.blue(color))" with "Color.BLUE", it gets much faster.

Found a workaround.

If I use my own bitwise operators instead of Color functions, it gets much faster...

  int i = 0;
  for (int y = 0; y < H; y++) {
     for (int x = 0; x < W; x++) {
         int color = pixels[i];
         int red = ((color & 0x00ff0000) >> 16);
         pixels[i] = (color & 0xff00ffff) | ((255 - red) << 16);
         //pixels[i] = Color.argb(Color.alpha(color), 255 - Color.red(color), Color.green(color), Color.blue(color));
         i++;
      }
  }
2
javaandroideclipseimage-processing

2 Answers

0
votes

You may want to consider using the ColorMatrix class to get this done: http://developer.android.com/reference/android/graphics/ColorMatrix.html

There is most likely considerable overhead involved when manipulating individual pixels the way you are doing it. The ColorMatrix class is your friend.

0
votes

I think if you replace this piece of code by this, it will be relatively fast

            int w = bitmap.getWidth();
        int h = bitmap.getHeight();
        int pixels[] = new int[w * h];
        bitmap.getPixels(pixels, 0, w, 0, 0, w, h);
        int n = w * h;
        for (int i = 0; i < n; i++) {
            int color = pixels[i];
            pixels[i] = Color.argb(Color.alpha(color), 255 - Color.red(color), Color.green(color), Color.blue(color));
        }
        bitmap.setPixels(pixels, 0, w, 0, 0, w, h);