仅适用于Android 4.0及以上的色带

Question

On emulators running Android 4.0 or 4.0.3, I am seeing horrible colour banding which I can't seem to get rid of. On every other Android version I have tested, gradients look smooth.

I have a SurfaceView which is configured as RGBX_8888, and the banding is not present in the rendered canvas. If I manually dither the image by overlaying a noise pattern at the end of rendering I can make the gradients smooth again, though obviously at a cost to performance which I'd rather avoid.

So the banding is being introduced later. I can only assume that, on 4.0+, my SurfaceView is being quantized to a lower bit-depth at some point between it being drawn and being displayed, and I can see from a screen capture that gradients are stepping 8 values at a time in each channel, suggesting a quantization to 555 (not 565).

I added the following to my Activity onCreate function, but it made no difference.

getWindow().setFormat(PixelFormat.RGBA_8888);
getWindow().addFlags(WindowManager.LayoutParams.FLAG_DITHER);

I also tried putting the above in onAttachedToWindow() instead, but there was still no change.

(I believe that RGBA_8888 is the default window format anyway for 2.2 and above, so it's little surprise that explicitly setting that format has no effect on 4.0+.)

Which leaves the question, if the source is 8888 and the destination is 8888, what is introducing the quantization/banding and why does it only appear on 4.0+?

Very puzzling. I wonder if anyone can shed some light?

Answer 1

Try dis..

BitmapFactory.Options options = new BitmapFactory.Options();
options.inPreferredConfig = Bitmap.Config.ARGB_8888;
Bitmap gradient = BitmapFactory.decodeResource(getResources(), R.drawable.gradient, options);

findViewById(R.id.main).setBackgroundDrawable(new BitmapDrawable(gradient));

Answer 2

Turning on the emulator "Use Host GPU" option fixed the color problems for me, credit goes to this answer https://stackoverflow.com/a/17166234/1287459

In my case I was using Android 4.2.2.