CODEWITHSUNDEEP
android
zer0stimulus
zer0stimulus

Reputation: 23606

Android: How to change hue of an Image?

I'm looking to change the hue of my background image (PNG) programmatically. How can this be done on Android?

Upvotes: 3

Views: 9219

Answers (3)

xjcl
xjcl

Reputation: 15309

If you wrap your Bitmap in an ImageView there is a very simple way:

ImageView circle = new ImageView(this);
circle.setImageBitmap(yourBitmap);
circle.setColorFilter(Color.RED);

My guess is this will be faster than modifying each pixel individually.

Upvotes: 0

user1922137
user1922137

Reputation:

I tested the accepted answer, unfortunately it returns a wrong result. I found and modified this code from here which works fine:

// hue-range: [0, 360] -> Default = 0
public static Bitmap hue(Bitmap bitmap, float hue) {
    Bitmap newBitmap = bitmap.copy(bitmap.getConfig(), true);
    final int width = newBitmap.getWidth();
    final int height = newBitmap.getHeight();
    float [] hsv = new float[3];

    for(int y = 0; y < height; y++){
        for(int x = 0; x < width; x++){
            int pixel = newBitmap.getPixel(x,y);
            Color.colorToHSV(pixel,hsv);
            hsv[0] = hue;
            newBitmap.setPixel(x,y,Color.HSVToColor(Color.alpha(pixel),hsv));
        }
    }

    bitmap.recycle();
    bitmap = null;

    return newBitmap;
}

Upvotes: 6

MandisaW
MandisaW

Reputation: 1021

The linked post has some good ideas, but the matrix math used for ColorFilter may be (a) complex overkill, and (b) introduce perceptible shifts in the resulting colors.

Modifying the solution given by janin here - https://stackoverflow.com/a/6222023/1303595 - I've based this version on Photoshop's 'Color' blend mode. It seems to avoid the image-darkening caused by PorterDuff.Mode.Multiply, and works very well for color-tinting desaturated/artificial-Black & White images without losing much contrast.

/*
 * Going for perceptual intent, rather than strict hue-only change. 
 * This variant based on Photoshop's 'Color' blending mode should look 
 * better for tinting greyscale images and applying an all-over color 
 * without tweaking the contrast (much)
 *     Final color = Target.Hue, Target.Saturation, Source.Luma
 * Drawback is that the back-and-forth color conversion introduces some 
 * error each time.
 */
public void changeHue (Bitmap bitmap, int hue, int width, int height) {
    if (bitmap == null) { return; }
    if ((hue < 0) || (hue > 360)) { return; }

    int size = width * height;
    int[] all_pixels = new int [size];
    int top = 0;
    int left = 0;
    int offset = 0;
    int stride = width;

    bitmap.getPixels (all_pixels, offset, stride, top, left, width, height);

    int pixel = 0;
    int alpha = 0;
    float[] hsv = new float[3];

    for (int i=0; i < size; i++) {
        pixel = all_pixels [i];
        alpha = Color.alpha (pixel);
        Color.colorToHSV (pixel, hsv);

        // You could specify target color including Saturation for
        // more precise results
        hsv [0] = hue;
        hsv [1] = 1.0f;

        all_pixels [i] = Color.HSVToColor (alpha, hsv);
    }

    bitmap.setPixels (all_pixels, offset, stride, top, left, width, height);
}

Upvotes: 2

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