Android virtual image method

Android blur images, blurred images, and frosted glass effects.

Effect

In Android, you can use RenderScript to conveniently implement this method:

private void blur(Bitmap bkg, View view, float radius) {        Bitmap overlay = Bitmap.createBitmap(view.getMeasuredWidth(), view.getMeasuredHeight(), Bitmap.Config.ARGB_8888);        Canvas canvas = new Canvas(overlay);        canvas.drawBitmap(bkg, -view.getLeft(), -view.getTop(), null);        RenderScript rs = RenderScript.create(this);        Allocation overlayAlloc = Allocation.createFromBitmap(rs, overlay);        ScriptIntrinsicBlur blur = ScriptIntrinsicBlur.create(rs, overlayAlloc.getElement());        blur.setInput(overlayAlloc);        blur.setRadius(radius);        blur.forEach(overlayAlloc);        overlayAlloc.copyTo(overlay);        view.setBackground(new BitmapDrawable(getResources(), overlay));        rs.destroy();    }

However, this method of RenderScript requires Android API17, that is, it must be implemented on Android 4.2.

Java native code can be used for implementation lower than Android4.2. But the efficiency will be much lower: This is completely a compromise and is not recommended.

/*     * This method was copied from http://stackoverflow.com/a/10028267/694378.     * The only modifications I've made are to remove a couple of Log     * statements which could slow things down slightly.     */    public Bitmap fastblur(Bitmap sentBitmap, int radius) {        // Stack Blur v1.0 from        // http://www.quasimondo.com/StackBlurForCanvas/StackBlurDemo.html        //        // Java Author: Mario Klingemann 
 
          // http://incubator.quasimondo.com        // created Feburary 29, 2004        // Android port : Yahel Bouaziz 
  
           // http://www.kayenko.com        // ported april 5th, 2012        // This is a compromise between Gaussian Blur and Box blur        // It creates much better looking blurs than Box Blur, but is        // 7x faster than my Gaussian Blur implementation.        //        // I called it Stack Blur because this describes best how this        // filter works internally: it creates a kind of moving stack        // of colors whilst scanning through the image. Thereby it        // just has to add one new block of color to the right side        // of the stack and remove the leftmost color. The remaining        // colors on the topmost layer of the stack are either added on        // or reduced by one, depending on if they are on the right or        // on the left side of the stack.        //        // If you are using this algorithm in your code please add        // the following line:        //        // Stack Blur Algorithm by Mario Klingemann 
   
            Bitmap bitmap = sentBitmap.copy(sentBitmap.getConfig(), true);        if (radius < 1) {            return (null);        }        int w = bitmap.getWidth();        int h = bitmap.getHeight();        int[] pix = new int[w * h];        bitmap.getPixels(pix, 0, w, 0, 0, w, h);        int wm = w - 1;        int hm = h - 1;        int wh = w * h;        int div = radius + radius + 1;        int r[] = new int[wh];        int g[] = new int[wh];        int b[] = new int[wh];        int rsum, gsum, bsum, x, y, i, p, yp, yi, yw;        int vmin[] = new int[Math.max(w, h)];        int divsum = (div + 1) >> 1;        divsum *= divsum;        int dv[] = new int[256 * divsum];        for (i = 0; i < 256 * divsum; i++) {            dv[i] = (i / divsum);        }        yw = yi = 0;        int[][] stack = new int[div][3];        int stackpointer;        int stackstart;        int[] sir;        int rbs;        int r1 = radius + 1;        int routsum, goutsum, boutsum;        int rinsum, ginsum, binsum;        for (y = 0; y < h; y++) {            rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;            for (i = -radius; i <= radius; i++) {                p = pix[yi + Math.min(wm, Math.max(i, 0))];                sir = stack[i + radius];                sir[0] = (p & 0xff0000) >> 16;                sir[1] = (p & 0x00ff00) >> 8;                sir[2] = (p & 0x0000ff);                rbs = r1 - Math.abs(i);                rsum += sir[0] * rbs;                gsum += sir[1] * rbs;                bsum += sir[2] * rbs;                if (i > 0) {                    rinsum += sir[0];                    ginsum += sir[1];                    binsum += sir[2];                } else {                    routsum += sir[0];                    goutsum += sir[1];                    boutsum += sir[2];                }            }            stackpointer = radius;            for (x = 0; x < w; x++) {                r[yi] = dv[rsum];                g[yi] = dv[gsum];                b[yi] = dv[bsum];                rsum -= routsum;                gsum -= goutsum;                bsum -= boutsum;                stackstart = stackpointer - radius + div;                sir = stack[stackstart % div];                routsum -= sir[0];                goutsum -= sir[1];                boutsum -= sir[2];                if (y == 0) {                    vmin[x] = Math.min(x + radius + 1, wm);                }                p = pix[yw + vmin[x]];                sir[0] = (p & 0xff0000) >> 16;                sir[1] = (p & 0x00ff00) >> 8;                sir[2] = (p & 0x0000ff);                rinsum += sir[0];                ginsum += sir[1];                binsum += sir[2];                rsum += rinsum;                gsum += ginsum;                bsum += binsum;                stackpointer = (stackpointer + 1) % div;                sir = stack[(stackpointer) % div];                routsum += sir[0];                goutsum += sir[1];                boutsum += sir[2];                rinsum -= sir[0];                ginsum -= sir[1];                binsum -= sir[2];                yi++;            }            yw += w;        }        for (x = 0; x < w; x++) {            rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;            yp = -radius * w;            for (i = -radius; i <= radius; i++) {                yi = Math.max(0, yp) + x;                sir = stack[i + radius];                sir[0] = r[yi];                sir[1] = g[yi];                sir[2] = b[yi];                rbs = r1 - Math.abs(i);                rsum += r[yi] * rbs;                gsum += g[yi] * rbs;                bsum += b[yi] * rbs;                if (i > 0) {                    rinsum += sir[0];                    ginsum += sir[1];                    binsum += sir[2];                } else {                    routsum += sir[0];                    goutsum += sir[1];                    boutsum += sir[2];                }                if (i < hm) {                    yp += w;                }            }            yi = x;            stackpointer = radius;            for (y = 0; y < h; y++) {                // Preserve alpha channel: ( 0xff000000 & pix[yi] )                pix[yi] = ( 0xff000000 & pix[yi] ) | ( dv[rsum] << 16 ) | ( dv[gsum] << 8 ) | dv[bsum];                rsum -= routsum;                gsum -= goutsum;                bsum -= boutsum;                stackstart = stackpointer - radius + div;                sir = stack[stackstart % div];                routsum -= sir[0];                goutsum -= sir[1];                boutsum -= sir[2];                if (x == 0) {                    vmin[y] = Math.min(y + r1, hm) * w;                }                p = x + vmin[y];                sir[0] = r[p];                sir[1] = g[p];                sir[2] = b[p];                rinsum += sir[0];                ginsum += sir[1];                binsum += sir[2];                rsum += rinsum;                gsum += ginsum;                bsum += binsum;                stackpointer = (stackpointer + 1) % div;                sir = stack[stackpointer];                routsum += sir[0];                goutsum += sir[1];                boutsum += sir[2];                rinsum -= sir[0];                ginsum -= sir[1];                binsum -= sir[2];                yi += w;            }        }        bitmap.setPixels(pix, 0, w, 0, 0, w, h);        return (bitmap);    }