Compare the pixel of the two different images, takes too long time

Question

I want to compare the pixel of the two different images. I am comparing the pixel of first image with all the pixels of the second Image. Here is my code stuff:

Answer 1

The order of your algorithm is n^4.

I guess that you could drive that down to n^3 if you

1. loop over all possible colors.
2. inside that loop, loop on each image
3. find the occurances of color i in each image
4. finally use an equation to increment Counter

If color i occurs x times in bitmap and y times in bitmap2,

Counter = Counter + x*y

Answer 2

If you're using API level 12 or above, there's a method called sameAs on Bitmap to do exactly what you're looking for. Otherwise, use getPixels and do something like:

int width = bitmap1.getWidth();
int height = bitmap1.getHeight();
int pixelCount = width * height;
int[] pixels1 = new int[pixelCount];
int[] pixels2 = new int[pixelCount];

bitmap1.getPixels(pixels1, 0, 0, 0, 0, width, height);
bitmap2.getPixels(pixels2, 0, 0, 0, 0, width, height);

for (int i = 0; i < pixelCount; i++) {
    if (pixels1[i] != pixels2[i]) {
        return false;
    }
}
return true;

Or if you really want to do the counter thing to see how many pixels are the same, go ahead and do that.

Actually, you can probably do something with the buffers too... Maybe something like

int width = bitmap1.getWidth();
int height = bitmap1.getHeight();
int pixelCount = width * height;
IntBuffer buffer1 = IntBuffer.allocate(pixelCount);
IntBuffer buffer2 = IntBuffer.allocate(pixelCount);
bitmap1.copyPixelsToBuffer(buffer1);
bitmap2.copyPixelsToBuffer(buffer2);
int result = buffer1.compareTo(buffer2);

I'm not sure how those two methods compare in performance, but it's something to play around with if you want.

Answer 3

Oh no, remember this in mind when you do image processing in Android.

Never use getPixel() or setPixel() continuously, like a loop, it will result in a really really bad performance, damn slow. Use getPixels() and setPixels() instead

Well, keep in mind that you need to read Android Documentation first.