Fast Bitmap Blur For Android SDK

Question

Currently in an Android application that I\'m developing I\'m looping through the pixels of an image to blur it. This takes about 30 seconds on a 640x480 image.

W

Answer 1

We tried to implement RenderScript blur like mentioned above in different answers. We were limited to use the v8 RenderScript version and that caused us a lot of trouble.

• Samsung S3 crashed randomly whenever we tried to use the renderscript
• Other devices (across different APIs) randomly showed different color issues

I want to share our dirty Java-only version which is slow and should be done on a separate thread and, if possible, before usage and therefore persisted.

private final Paint mPaint = new Paint();

public Bitmap blur(final String pathToBitmap) {
    final BitmapFactory.Options options = new BitmapFactory.Options();
    final Bitmap normalOne = BitmapFactory.decodeFile(pathToBitmap, options);
    final Bitmap resultBitmap = Bitmap.createBitmap(options.outWidth, options.outHeight, Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(resultBitmap);
    mPaint.setAlpha(180);
    canvas.drawBitmap(normalOne, 0, 0, mPaint);
    int blurRadius = 12;
    for (int row = -blurRadius; row < blurRadius; row += 2) {
        for (int col = -blurRadius; col < blurRadius; col += 2) {
            if (col * col + row * row <= blurRadius * blurRadius) {
                mPaint.setAlpha((blurRadius * blurRadius) / ((col * col + row * row) + 1) * 2);
                canvas.drawBitmap(normalOne, row, col, mPaint);
            }
        }
    }
    normalOne.recycle();
    return resultBitmap;
}

This solution is far from perfect but creates a reasonable blur effect based on the fact, that it draws highly transparent version of the same image on top of a barely transparent "sharp" version. The alpha depends on the distance to the origin.

You can adjust some "magic numbers" to your needs. I just wanted to share that "solution" for everybody who has issues with the v8 support version of RenderScript.