How to iterate through pixels in a more efficient way?

I'm getting an Image and convert it into a Bitmap. To check if the color of a pixel is between two values, I iterate through every single pixel of the given Bitmap. I create a new Bitmap, change the pixel if it is between these values and set.Pixel() on the new Bitmap, or leave the Pixel as it is and set it also on the new Bitmap. I reduced the Bitmap.Config from ARGB-8888 to RGB_565 but it is still unbeleavable slow and shows in debug "The application may be doing too much work on its main thread."

Is there a better way to do that and make the app faster?

<!-- language: java -->

 width = bitmap.getWidth();
        heigth = bitmap.getHeight();
        Bitmap newBitmap = Bitmap.createBitmap(width, heigth, Bitmap.Config.RGB_565);

        for(int x = 0; x < width; x++){
            for(int y = 0; y < heigth; y++){
                int pixel = bitmap.getPixel(x,y);
                float[] pixelHue = getHsv(pixel);
                if(pixelHue[0] > 170 && pixelHue[0] < 250 ){
                 //Change the Pixel
                    pixelHue[0] = pixelHue[0] - 17;
                    int newColor = setRgb(pixelHue);
                    newBitmap.setPixel(x, y, newColor);
                }
                else{
                      //leave the Pixel as it is
                    newBitmap.setPixel(x, y, pixel);
                }

            }
        }
        return newBitmap;
    }



private float[] getHsv (int pixel){
         int a = Color.alpha(pixel);
         int r = Color.red(pixel);
         int g = Color.green(pixel);
         int b = Color.blue(pixel);
         float[] hsv = new float[3];
         Color.RGBToHSV(r, g, b, hsv);
        return hsv;
    }


private int setRgb (float[] hsv){
        int rgb;
        rgb = Color.HSVToColor(hsv);
        return rgb;
    }

> but I need to check the hue value of a pixels color to indicate, if the color is in my range

Correct, but you don't need to convert the pixel to an HSV value every time. You can do the conversion once and then store the result.

So the basic structure of your code might be something like:

HashMap<Integer, Integer> pixels = new HashMap<Integer, Integer>(); // instance variable of your class

for(…)
{
    for (…)
    {
        int pixel = bitmap.getPixel(x,y)
        int pixelHue = getPixelHue( pixel );
        newBitmap.setPixel(x, y, pixelHue);
    }
}

…

private int getPixelHue(int pixel)
{
    Integer pixelHue = pixels.get(pixel);

    if (pixelHue == null) // you haven't attempted to convert this pixel yet
    {
        float[] hsv = getHsv(pixel);

        if(hsv[0] > 170 && hsv[0] < 250 )
        {
            // Change the hue value of the hsv color
            hsv[0] = hsv[0] - 17;
            pixelHue = setRgb(hsv); // conversion done
        }
        else
        {
            pixelHue = pixel; // no conversion needed
        }

        pixels.put(pixel, pixelHue); // store result so we don't need to reconvert
    }

    return pixelHue;
}

So the HashMap will originally be empty. As you process a pixel of a unique color you will do the HSV conversion and hue conversion, if necessary, and store the result in the HashMap. The next time you process this pixel color you don't need to repeat the conversion process.