Drawable => grayscale

Question

What would be the right way to turn a color Drawable into a grayscale one (to indicate disabled state)?

EDIT:
B/W => grayscale

Answer 1

Apparently you can use the ColorMatrix class to do any sort of color-space transformations. It has a setSaturation() method that easily creates a color-to-grayscale transformation (zeroes saturation) for you.

So, you can use that filter to paint a new copy of the image. I haven't tried this, but it should work:

Bitmap grayscaleBitmap = Bitmap.createBitmap(
    colorBitmap.getWidth(), colorBitmap.getHeight(),
    Bitmap.Config.RGB_565);

Canvas c = new Canvas(grayscaleBitmap);
Paint p = new Paint();
ColorMatrix cm = new ColorMatrix();

cm.setSaturation(0);
ColorMatrixColorFilter filter = new ColorMatrixColorFilter(cm);
p.setColorFilter(filter); 
c.drawBitmap(colorBitmap, 0, 0, p);