A gaussian blur transformation for picasso, using renderscript.

GaussianBlurTransformation.java

import android.content.Context;
import android.graphics.Bitmap;
import android.support.v8.renderscript.Allocation;
import android.support.v8.renderscript.Element;
import android.support.v8.renderscript.RenderScript;
import android.support.v8.renderscript.ScriptIntrinsicBlur;
import com.squareup.picasso.Transformation;

public class GaussianBlurTransformation implements Transformation {

	private final RenderScript _renderScript;
	private final ScriptIntrinsicBlur _scriptIntrinsicBlur;

	/**
	 * Creates a new GaussianBlurTransformation.
	 * 
	 * Uses a default blur radius of 25f.
	 * 
	 * @param context The context to create the RenderScript instance from.
	 */
	public GaussianBlurTransformation(final Context context) {
		this(context, 25f);
	}

	/**
	 * Creates a new GaussianBlurTransformation.
	 * 
	 * @param context The context to create the RenderScript instance from.
	 * @param radius The blur radius.
	 */
	public GaussianBlurTransformation(final Context context, final float radius) {
		_renderScript = RenderScript.create(context);
		_scriptIntrinsicBlur = ScriptIntrinsicBlur.create(_renderScript, Element.U8_4(_renderScript));
		_scriptIntrinsicBlur.setRadius(radius);
	}

	@Override public Bitmap transform(final Bitmap source) {
		final Bitmap result = Bitmap.createBitmap(source.getWidth(), source.getHeight(), Bitmap.Config.ARGB_8888);

		final Allocation allocationInput = Allocation.createFromBitmap(_renderScript, source);
		final Allocation allocationOutput = Allocation.createFromBitmap(_renderScript, result);

		// perform the transformation
		_scriptIntrinsicBlur.setInput(allocationInput);
		_scriptIntrinsicBlur.forEach(allocationOutput);

		// copy the final bitmap created by the output Allocation to the outBitmap
		allocationOutput.copyTo(result);

		source.recycle();
		_scriptIntrinsicBlur.destroy();

		return result;
	}
	
	// allow picasso to cache the result of this trnasformation
	@Override public String key() {
		return "gauss-blur";
	}
}