Android: fast bitmap blur?

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I finally found a suitable solution:

  • RenderScript allows implementing heavy computations which are scaled transparently to all cores available on the executing device. I’ve come to the conclusion, that with respect to a reasonable balance of performance and implementation complexity, this is a better approach than JNI or shaders.
  • Since API Level 17, there is the ScriptIntrinsicBlur class available from the API. This is exactly what I’ve been looking for, namely a high level, hardware-accelerated Gaussian blur implementation.
  • ScriptIntrinsicBlur is now a part of the android support library (v8) which supports Froyo and above (API>8). The android developer blog post on the support RenderScript library has some basic tips on how to use it.

However, the documentation on the ScriptIntrinsicBlur class is very rare and I’ve spent some more time on figuring out the correct invocation arguments. For bluring an ordinary ARGB_8888-typed bitmap named photo, here they are:

final RenderScript rs = RenderScript.create( myAndroidContext );
final Allocation input = Allocation.createFromBitmap( rs, photo, Allocation.MipmapControl.MIPMAP_NONE, Allocation.USAGE_SCRIPT );
final Allocation output = Allocation.createTyped( rs, input.getType() );
final ScriptIntrinsicBlur script = ScriptIntrinsicBlur.create( rs, Element.U8_4( rs ) );
script.setRadius( myBlurRadius /* e.g. 3.f */ );
script.setInput( input );
script.forEach( output );
output.copyTo( photo );

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