Replacing a color in a Bitmap

Question

I have images which I display in my app. They are downloaded from the web. These images are pictures of objects on an almost-white background. I want this background to be white (#FFFFFF). I figure, if I look at pixel 0,0 (which should always be off-white), I can get the color value and replace every pixel in the image having that value with white.

This question has been asked before and the answer seems to be this:

int intOldColor = bmpOldBitmap.getPixel(0,0);

Bitmap bmpNewBitmap = Bitmap.createBitmap(bmpOldBitmap.getWidth(), bmpOldBitmap.getHeight(), Bitmap.Config.RGB_565);
Canvas c = new Canvas(bmpNewBitmap);
Paint paint = new Paint();

ColorFilter filter = new LightingColorFilter(intOldColor, Color.WHITE);
paint.setColorFilter(filter);
c.drawBitmap(bmpOriginal, 0, 0, paint);

However, this isn't working.

After running this code, the entire image seems to be the color I was wanting to remove. As in, the entire image is 1 solid color now.

I was also hoping to not have to loop through every pixel in the entire image.

Any ideas?

The LightingColorFilter usage here is definitely not going to work like you expect because there is nothing that says "only apply this operation to THIS color." The first argument color is the multiplication factor which gets applied to EVERY pixel in your image. The second argument, WHITE (0xFFFFFF) is then ADDED to every pixel making the whole thing white. — nvuono, Sep 11 '13 at 18:38

score 16 · Answer 1 · edited Jun 05 '18 at 19:19

Here is a method I created for you to replace a specific color for the one you want. Note that all the pixels will get scanned on the Bitmap and only the ones that are equal will be replaced for the one you want.

     private Bitmap changeColor(Bitmap src, int colorToReplace, int colorThatWillReplace) {
        int width = src.getWidth();
        int height = src.getHeight();
        int[] pixels = new int[width * height];
        // get pixel array from source
        src.getPixels(pixels, 0, width, 0, 0, width, height);

        Bitmap bmOut = Bitmap.createBitmap(width, height, src.getConfig());

        int A, R, G, B;
        int pixel;

         // iteration through pixels
        for (int y = 0; y < height; ++y) {
            for (int x = 0; x < width; ++x) {
                // get current index in 2D-matrix
                int index = y * width + x;
                pixel = pixels[index];
                if(pixel == colorToReplace){
                    //change A-RGB individually
                    A = Color.alpha(colorThatWillReplace);
                    R = Color.red(colorThatWillReplace);
                    G = Color.green(colorThatWillReplace);
                    B = Color.blue(colorThatWillReplace);
                    pixels[index] = Color.argb(A,R,G,B); 
                    /*or change the whole color
                    pixels[index] = colorThatWillReplace;*/
                }
            }
        }
        bmOut.setPixels(pixels, 0, width, 0, 0, width, height);
        return bmOut;
    }

I hope that helped :)

yes it is mutable.. i dont know much about this but as i load image from gallery it needs to mutable.. if yes then my image is mutable — Mustanser Iqbal, Oct 27 '15 at 19:05
Assembly of the new color should be done outside the loop to reduce overall time to complete this method. — Bob Lissner, Mar 22 '19 at 05:38

Replacing a color in a Bitmap

1 Answers1

Linked