将位图数组转换为YUV(YCbCr NV21)

如何将BitmapFactory.decodeFile()返回的Bitmap转换为YUV格式(simillar到相机的onPreviewFrame()返回字节数组)?

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这是一些实际工作的代码:

  // untested function byte [] getNV21(int inputWidth, int inputHeight, Bitmap scaled) { int [] argb = new int[inputWidth * inputHeight]; scaled.getPixels(argb, 0, inputWidth, 0, 0, inputWidth, inputHeight); byte [] yuv = new byte[inputWidth*inputHeight*3/2]; encodeYUV420SP(yuv, argb, inputWidth, inputHeight); scaled.recycle(); return yuv; } void encodeYUV420SP(byte[] yuv420sp, int[] argb, int width, int height) { final int frameSize = width * height; int yIndex = 0; int uvIndex = frameSize; int a, R, G, B, Y, U, V; int index = 0; for (int j = 0; j < height; j++) { for (int i = 0; i < width; i++) { a = (argb[index] & 0xff000000) >> 24; // a is not used obviously R = (argb[index] & 0xff0000) >> 16; G = (argb[index] & 0xff00) >> 8; B = (argb[index] & 0xff) >> 0; // well known RGB to YUV algorithm Y = ( ( 66 * R + 129 * G + 25 * B + 128) >> 8) + 16; U = ( ( -38 * R - 74 * G + 112 * B + 128) >> 8) + 128; V = ( ( 112 * R - 94 * G - 18 * B + 128) >> 8) + 128; // NV21 has a plane of Y and interleaved planes of VU each sampled by a factor of 2 // meaning for every 4 Y pixels there are 1 V and 1 U. Note the sampling is every other // pixel AND every other scanline. yuv420sp[yIndex++] = (byte) ((Y < 0) ? 0 : ((Y > 255) ? 255 : Y)); if (j % 2 == 0 && index % 2 == 0) { yuv420sp[uvIndex++] = (byte)((V<0) ? 0 : ((V > 255) ? 255 : V)); yuv420sp[uvIndex++] = (byte)((U<0) ? 0 : ((U > 255) ? 255 : U)); } index ++; } } } 

以下是将Bitmap转换为Yuv(NV21)格式的代码。

 void yourFunction(){ // mBitmap is your bitmap int mWidth = mBitmap.getWidth(); int mHeight = mBitmap.getHeight(); int[] mIntArray = new int[mWidth * mHeight]; // Copy pixel data from the Bitmap into the 'intArray' array mBitmap.getPixels(mIntArray, 0, mWidth, 0, 0, mWidth, mHeight); // Call to encoding function : convert intArray to Yuv Binary data encodeYUV420SP(data, intArray, mWidth, mHeight); } static public void encodeYUV420SP(byte[] yuv420sp, int[] rgba, int width, int height) { final int frameSize = width * height; int[] U, V; U = new int[frameSize]; V = new int[frameSize]; final int uvwidth = width / 2; int r, g, b, y, u, v; for (int j = 0; j < height; j++) { int index = width * j; for (int i = 0; i < width; i++) { r = Color.red(rgba[index]); g = Color.green(rgba[index]); b = Color.blue(rgba[index]); // rgb to yuv y = (66 * r + 129 * g + 25 * b + 128) >> 8 + 16; u = (-38 * r - 74 * g + 112 * b + 128) >> 8 + 128; v = (112 * r - 94 * g - 18 * b + 128) >> 8 + 128; // clip y yuv420sp[index] = (byte) ((y < 0) ? 0 : ((y > 255) ? 255 : y)); U[index] = u; V[index++] = v; } } 

如果使用java将Bitmap转换为YUV byte []对你来说太慢了,你可以试试谷歌的libyuv

通过OpenCV库,您可以用一个原生OpenCV线替换encodeYUV420SP java函数,它的速度提高了约4倍

 Mat mFrame = Mat(height,width,CV_8UC4,pFrameData).clone(); 

完整的例子:

Java方面:

  Bitmap bitmap = mTextureView.getBitmap(mWidth, mHeight); int[] argb = new int[mWidth * mHeight]; // get ARGB pixels and then proccess it with 8UC4 opencv convertion bitmap.getPixels(argb, 0, mWidth, 0, 0, mWidth, mHeight); // native method (NDK or CMake) processFrame8UC4(argb, mWidth, mHeight); 

原生方(NDK):

 JNIEXPORT jint JNICALL com_native_detector_Utils_processFrame8UC4 (JNIEnv *env, jobject object, jint width, jint height, jintArray frame) { jint *pFrameData = env->GetIntArrayElements(frame, 0); // it is the line: Mat mFrame = Mat(height,width,CV_8UC4,pFrameData).clone(); // the next only is a extra example to gray convertion: Mat mout; cvtColor(mFrame, mout,CV_RGB2GRAY); int objects = face_detection(env, mout); env->ReleaseIntArrayElements(frame, pFrameData, 0); return objects; } 

bmp文件将采用RGB888格式,因此您需要将其转换为YUV。 我没有在Android中遇到任何api会为你做这件事。

但你可以自己做,看看这个链接如何…

首先计算rgb数据:

 r=(p>>16) & 0xff; g=(p>>8) & 0xff; b= p & 0xff; y=0.2f*r+0.7*g+0.07*b; u=-0.09991*r-0.33609*g+0.436*b; v=0.615*r-0.55861*g-0.05639*b; 

y,u和v是yuv矩阵的合成物。