Question

I’m trying to make an app that will take two pictures you specify via editText, compare the colors of each pixel on both images and create a new picture (bitmap) (that you can save to the sd card) containing the differences between the two original pictures.

I’m having a problem with creating this new bitmap. How can I achieve my goal? I don’t really know how to do this, do I create the new bitmap first and then write into it, or do I get the differences first and then draw a bitmap from that? The pictures will be approx. 300×300 px.

Answer 1

this code is just out of my head and untested but it should get you on the right track.

final int w1 = b1.getWidth();
final int w2 = b2.getWidth();
final int h1 = b1.getHeight();
final int h2 = b2.getHeight();
final int w = Math.max(w1, w2);
final int h = Math.max(h2, h2);

Bitmap compare = Bitmap.createBitmap(w, h, Config.ARGB_8888);

int color1, color2, a, r, g, b;

for (int x = 0; x < w; x++) {
    for (int y = 0; y < h; y++) {
        if (x < w1 && y < h1) {
            color1 = b1.getPixel(x, y);
        } else {
            color1 = Color.BLACK;
        }
        if (x < w2 && y < h2) {
            color2 = b2.getPixel(x, y);
        } else {
            color2 = Color.BLACK;
        }
        a = Math.abs(Color.alpha(color1) - Color.alpha(color2));
        r = Math.abs(Color.red(color1) - Color.red(color2));
        g = Math.abs(Color.green(color1) - Color.green(color2));
        b = Math.abs(Color.blue(color1) - Color.blue(color1));

        compare.setPixel(x, y, Color.argb(a, r, g, b));
    }
}
b1.recycle();
b2.recycle();