Android 实时滤镜 高斯模糊（带源码）

最近在做一个这样一个需求，一个控件可以实时预览摄像头的内容，并且对此图像进行高斯模糊处理，现在来记录一下。 

1. 1. 1. 1. 1. 1. 1. 

基本的实现思路

1，摄像头实时预览的数据会回调给onPreviewFrame(byte[] data, Camera camera) ，通过这个获取YUV格式的数据。 
2，将YUV转换成RGB数组。 
3，cpu计算rgb数组或者gpu来处理图像。（这里用的cpu计算） 
github上有一个GPU实现高斯滤镜的开源项目，但是我觉得它的高斯模糊实现的不够好。 
android-gpuimage

开始onPreviewFrame（data）YUV420SP转RGBdoBlur()CPU计算结束

一，YUV420SP

在onPreviewFrame文档中有这么一段话。

 /**
     * Callback interface used to deliver copies of preview frames as
     * they are displayed.
     *
     * @see #setPreviewCallback(Camera.PreviewCallback)
     * @see #setOneShotPreviewCallback(Camera.PreviewCallback)
     * @see #setPreviewCallbackWithBuffer(Camera.PreviewCallback)
     * @see #startPreview()
     */
    public interface PreviewCallback
    {
        /**
         * Called as preview frames are displayed.  This callback is invoked
         * on the event thread {@link #open(int)} was called from.
         *
         * 
If using the {@link android.graphics.ImageFormat#YV12} format,
         * refer to the equations in {@link Camera.Parameters#setPreviewFormat}
         * for the arrangement of the pixel data in the preview callback
         * buffers.
         *
         * @param data the contents of the preview frame in the format defined
         *  by {@link android.graphics.ImageFormat}, which can be queried
         *  with {@link android.hardware.Camera.Parameters#getPreviewFormat()}.
         *  If {@link android.hardware.Camera.Parameters#setPreviewFormat(int)}
         *             is never called, the default will be the YCbCr_420_SP
         *             (NV21) format.
         * @param camera the Camera service object.
         */
        void onPreviewFrame(byte[] data, Camera camera);
    };
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默认输出的格式YUV420SP,注释中的YCbCr就是YUV。 
YUV，分为三个分量，“Y”表示明亮度（Luminance或Luma），也就是灰度值； 
而“U”和“V” 表示的则是色度（Chrominance或Chroma），作用是描述影像色彩及饱和度，用于指定像素的颜色。

下面是拥有8个像素的YUV数组[4*2]，YUV420SP即4个Y对应一个UV，如图，Y1，Y2，Y9，Y10对应U1，V1。 

二，YUV420SP转RGB

最主要是下面的转换公式：

//ITU-R BT.601 conversion

R = 1.164*(Y-16)+1.596*(Cr-128)
G = 1.164*(Y-16)-0.392*(Cb-128)-0.813*(Cr-128)
B = 1.164*(Y-16)+2.017*(Cb-128)
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或者

R'' = Y + 1.140*V
G'' = Y - 0.394*U - 0.581*V
B'' = Y + 2.032*U
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只是工业标准不同而已。下面截取android-gpu-image上面的代码并添加一些注释，网上有很多转换的方法，但是这个方法性能非常ok，耗时在10-20ms。为了最大可能获取性能，代码中乘法等都变成了位操作和加法的方式。

void YUVtoARBG(JNIEnv * env, jobject obj, jbyteArray yuv420sp, jint width, jint height, jintArray rgbOut)
{
    int             sz;
    int             i;
    int             j;
    int             Y;
    int             Cr = 0;
    int             Cb = 0;
    int             pixPtr = 0;  //Y所占的空间
    int             jDiv2 = 0;  //uv前面行所占的空间
    int             R = 0;
    int             G = 0;
    int             B = 0;
    int             cOff;
    int w = width;
    int h = height;
    sz = w * h;

    jint *rgbData = (jint*) ((*env)->GetPrimitiveArrayCritical(env, rgbOut, 0));
    jbyte* yuv = (jbyte*) (*env)->GetPrimitiveArrayCritical(env, yuv420sp, 0);

    for(j = 0; j < h; j++) {
             pixPtr = j * w;     //Y所占的空间
             jDiv2 = j >> 1;    //除以2向下取整
             for(i = 0; i < w; i++) {
                     Y = yuv[pixPtr];
                     if(Y < 0) Y += 255;
                      //用位运算判断是奇数还是偶数
                     if((i & 0x1) != 1) {
                             cOff = sz + jDiv2 * w + (i >> 1) * 2;  //计算 UV的位置  (i>>1)*2就是为了变成偶数  向下取整  因为U的游标都是偶数位
                             Cb = yuv[cOff];
                             if(Cb < 0) Cb += 127; else Cb -= 128;
                             Cr = yuv[cOff + 1];
                             if(Cr < 0) Cr += 127; else Cr -= 128;
                     }

                     //ITU-R BT.601 conversion
                     //
                     //     R = 1.164*(Y-16)+1.596*(Cr-128)
                     //     G = 1.164*(Y-16)-0.392*(Cb-128)-0.813*(Cr-128)
                     //     B = 1.164*(Y-16)+2.017*(Cb-128)
                     //

                     Y = Y + (Y >> 3) + (Y >> 5) + (Y >> 7);    //Y=Y+Y*0.125+0.03125+0.00078
                     R = Y + Cb + (Cb >> 1) + (Cb >> 4) + (Cb >> 5);
                     if(R < 0) R = 0; else if(R > 255) R = 255;
                     G = Y - Cb + (Cb >> 3) + (Cb >> 4) - (Cr >> 1) + (Cr >> 3);
                     if(G < 0) G = 0; else if(G > 255) G = 255;
                     B = Y + (Cr << 1) + (Cr >> 6);
                     if(B < 0) B = 0; else if(B > 255) B = 255;
                     rgbData[pixPtr++] = 0xff000000 + (R << 16) + (G << 8) + B;
             }
    }

    (*env)->ReleasePrimitiveArrayCritical(env, rgbOut, rgbData, 0);
    (*env)->ReleasePrimitiveArrayCritical(env, yuv420sp, yuv, 0);
}
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三，高斯模糊

至于原理请看：高斯模糊 
这里用的FastBlur，之前考虑了RenderScript ,后来发现在实际使用中，最下方会出现闪烁的现象，故放弃。

public static Bitmap doBlur(Bitmap sentBitmap, int radius, boolean canReuseInBitmap) {

        // 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;
        if (canReuseInBitmap) {
            bitmap = sentBitmap;
        } else {
            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);
    }
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为了获取进一步的性能，我们可以做以下操作： 
1，设置一个vector，当vector中存在对象时，丢弃当前帧，绘制完后，清空vector，保证vector最多只有一个对象。 
2，先对图片进行缩小处理，高斯模糊后再放大。

        //每次只处理一个图像，若前面的图像未处理完成，舍弃当前图像，提升性能
        if(mVector.isEmpty()){
            Log.i(TAG, "byte data ADD");
            mVector.add(data);
            new DrawTask().execute();
        }
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因为onPreviewFrame()在主线程中，所以绘图一定要异步进行。

这里一个例子，提供大家参考：下载地址