How to use the Renderscript blurring effect without artifacts?

Question

Background

There are plenty of places (including here) to show how to use Renderscript to blur images, as such:

@TargetApi(VERSION_CODES.JELLY_BEAN_MR1)
public static Bitmap renderScriptBlur(Context context, Bitmap srcBitmap, @FloatRange(from = 0.0f, to = 25.0f) float radius) {
    if (srcBitmap == null)
        return null;
    Bitmap outputBitmap = null;
    RenderScript rs = null;
    try {
        rs = RenderScript.create(context);
        outputBitmap = Bitmap.createBitmap(srcBitmap.getWidth(), srcBitmap.getHeight(), Bitmap.Config.ARGB_8888);
        final Canvas canvas = new Canvas(outputBitmap);
        canvas.drawBitmap(srcBitmap, 0, 0, null);
        Allocation overlayAlloc = Allocation.createFromBitmap(rs, outputBitmap);
        ScriptIntrinsicBlur blur = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
        blur.setInput(overlayAlloc);
        blur.setRadius(radius);
        blur.forEach(overlayAlloc);
        overlayAlloc.copyTo(outputBitmap);
        return outputBitmap;
    } catch (Exception ex) {
        if (outputBitmap != null)
            outputBitmap.recycle();
        return srcBitmap;
    } finally {
        if (rs != null)
            rs.destroy();
    }
}

The problem

Usually it works great, but when using some images and/or radius-settings, the output image has artifacts that look like scan-lines:

What I've tried

I've found that there is a nicer blurring solutions (like here), but they don't use Renderscript and are also slow and memory-consuming.

I've also tried to make the input image smaller, but the output still has scanlines artifacts.

Finally, I've also reported about this, here.

The question

Is it possible to use Renderscript to blur images without those Artifcats? Is there anything wrong with what I wrote?

Answer 1

The problem was with the algorithm I used. Thanks to this github project, I've found the issue (which is probably not using the correct type fot the allocation) and used a nicer approach:

private static final AtomicReference<RenderScript> sRenderscript = new AtomicReference<>();


public static Bitmap blur(Context context, Bitmap bitmap) {
    return blur(context, bitmap, 4, false, false);
}

public static Bitmap blur(Context context, Bitmap bitmap, float radius) {
    return blur(context, bitmap, radius, false, false);
}

public static Bitmap blur(Context context, Bitmap bitmapOriginal, @FloatRange(from = 0.0f, to = 25.0f) float radius, boolean overrideOriginal, boolean recycleOriginal) {
    if (bitmapOriginal == null || bitmapOriginal.isRecycled())
        return null;
    RenderScript rs = sRenderscript.get();
    if (rs == null)
        if (!sRenderscript.compareAndSet(null, rs = RenderScript.create(context)) && rs != null)
            rs.destroy();
        else
            rs = sRenderscript.get();
    final Bitmap inputBitmap = bitmapOriginal.getConfig() == Config.ARGB_8888 ? bitmapOriginal : bitmapOriginal.copy(Config.ARGB_8888, true);
    final Bitmap outputBitmap = overrideOriginal ? bitmapOriginal : Bitmap.createBitmap(bitmapOriginal.getWidth(), bitmapOriginal.getHeight(), Config.ARGB_8888);
    final Allocation input = Allocation.createFromBitmap(rs, inputBitmap);
    final Allocation output = Allocation.createTyped(rs, input.getType());
    final ScriptIntrinsicBlur script = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
    script.setRadius(radius);
    script.setInput(input);
    script.forEach(output);
    if (recycleOriginal && !overrideOriginal)
        bitmapOriginal.recycle();
    output.copyTo(outputBitmap);
    return outputBitmap;
}

Now it all works nicely.