Android视频编码——RGBARGBBGRABGR转YUV420PYUV420SP

Posted 2022-08-01 湖广午王

做视频处理一般都会涉及到RGBA与YUV颜色格式的相互转换，理论知识就不多说了，直接贴出转换公式来：

Y’= 0.299*R’ + 0.587*G’ + 0.114*B’
U’= -0.147*R’ - 0.289*G’ + 0.436*B’ = 0.492*(B’- Y’)
V’= 0.615*R’ - 0.515*G’ - 0.100*B’ = 0.877*(R’- Y’)
R’ = Y’ + 1.140*V’
G’ = Y’ - 0.394*U’ - 0.581*V’
B’ = Y’ + 2.032*U’

根据公式，写出相应的代码就OK了。当然编码需要考虑效率问题，在转换运算中应该尽量避免浮点运算。以下代码实现相对简介，效率也还可以，如果需要更高的转换效率，可以用空间换时间，采用查表法来做。如果有更好的方法，希望可以指点我一下，感激不尽。
JNI实现代码如下：

#include "jni.h"

#define max(x,y)  (x>y?x:y)
#define min(x,y)  (x<y?x:y)
#define y(r,g,b)  (((66 * r + 129 * g + 25 * b + 128) >> 8) + 16)
#define u(r,g,b)  (((-38 * r - 74 * g + 112 * b + 128) >> 8) + 128)
#define v(r,g,b)  (((112 * r - 94 * g - 18 * b + 128) >> 8) + 128)
#define color(x)  ((unsigned char)((x < 0) ? 0 : ((x > 255) ? 255 : x)))

#define RGBA_YUV420SP   0x00004012
#define BGRA_YUV420SP   0x00004210
#define RGBA_YUV420P    0x00014012
#define BGRA_YUV420P    0x00014210
#define RGB_YUV420SP    0x00003012
#define RGB_YUV420P     0x00013012
#define BGR_YUV420SP    0x00003210
#define BGR_YUV420P     0x00013210

/**
*   type 0-3位表示b的偏移量
*        4-7位表示g的偏移量
*        8-11位表示r的偏移量
*        12-15位表示rgba一个像素所占的byte
*        16-19位表示yuv的类型，0为420sp，1为420p
*/

void rgbaToYuv(int width,int height,unsigned char * rgb,unsigned char * yuv,int type)
    const int frameSize = width * height;
    const int yuvType=(type&0x10000)>>16;
    const int byteRgba=(type&0x0F000)>>12;
    const int rShift=(type&0x00F00)>>8;
    const int gShift=(type&0x000F0)>>4;
    const int bShift= (type&0x0000F);
    const int uIndex=0;
    const int vIndex=yuvType; //yuvType为1表示YUV420p,为0表示420sp

    int yIndex = 0;
    int uvIndex[2]=frameSize,frameSize+frameSize/4;

    unsigned char R, G, B, Y, U, V;
    unsigned int index = 0;
    for (int j = 0; j < height; j++) 
       for (int i = 0; i < width; i++) 
           index = j * width + i;

           R = rgb[index*byteRgba+rShift]&0xFF;
           G = rgb[index*byteRgba+gShift]&0xFF;
           B = rgb[index*byteRgba+bShift]&0xFF;

           Y = y(R,G,B);
           U = u(R,G,B);
           V = v(R,G,B);

           yuv[yIndex++] = color(Y);
           if (j % 2 == 0 && index % 2 == 0) 
               yuv[uvIndex[uIndex]++] =color(U);
               yuv[uvIndex[vIndex]++] =color(V);
           
       
    



extern "C" 

    void Java_com_aiya_jni_DataConvert_rgbaToYuv
      (JNIEnv * env, jobject obj, jbyteArray rgba, jint width, jint height,
      jbyteArray yuv,jint type)
        jbyte * rgbaBuffer = env->GetByteArrayElements(rgba,0);
        unsigned char * cRgba=(unsigned char *)rgbaBuffer;
        jbyte* yuvBuffer = env->GetByteArrayElements(yuv,0);
        unsigned char * cYuv=(unsigned char *)yuvBuffer;
        rgbaToYuv(width,height,cRgba,cYuv,type);
        env->ReleaseByteArrayElements(rgba, rgbaBuffer, 0);
        env->ReleaseByteArrayElements(yuv, yuvBuffer, 0);