基于Video4Linux的USB摄像头图像采集后显示为黑白？

我的摄像头，palette为yuv420.抓取一帧图像后在framebuffer里显示为黑白。估计需要把yuv420转rgb,请问谁能提供一下转换代码？网上找的这个代码不行，调用后图像就全黑了~



static long int crv_tab[256];
static long int cbu_tab[256];
static long int cgu_tab[256];
static long int cgv_tab[256];
static long int tab_76309[256];
static unsigned char clp[1024]; //for clip in CCIR601

注：我把一帧的首地址传给src,frambuffer的首地址传给dst_on,width=640 and height=480为一帧的大小。
void YUV2RGB420(unsigned char *src, unsigned char *dst_ori,
int width,int height)
{
unsigned char *src0;
unsigned char *src1;
unsigned char *src2;
int y1,y2,u,v;
unsigned char *py1,*py2;
int i,j, c1, c2, c3, c4;
unsigned char *d1, *d2, *d3;

//Initialization
src0=src;
src1=src+width*height;
src2=src+width*height+width*height/4;

py1=src0;
py2=py1+width;
d1=dst_ori;
d2=d1+3*width;
for (j = 0; j < height; j += 2) {
for (i = 0; i < width; i += 2) {

u = *src1++;
v = *src2++;

c1 = crv_tab[v];
c2 = cgu_tab;
c3 = cgv_tab[v];
c4 = cbu_tab;

//up-left
y1 = tab_76309[*py1++];
*d1++ = clp[384+((y1 + c1)>>16)];
*d1++ = clp[384+((y1 - c2 - c3)>>16)];
*d1++ = clp[384+((y1 + c4)>>16)];

//down-left
y2 = tab_76309[*py2++];
*d2++ = clp[384+((y2 + c1)>>16)];
*d2++ = clp[384+((y2 - c2 - c3)>>16)];
*d2++ = clp[384+((y2 + c4)>>16)];

//up-right
y1 = tab_76309[*py1++];
*d1++ = clp[384+((y1 + c1)>>16)];
*d1++ = clp[384+((y1 - c2 - c3)>>16)];
*d1++ = clp[384+((y1 + c4)>>16)];

//down-right
y2 = tab_76309[*py2++];
*d2++ = clp[384+((y2 + c1)>>16)];
*d2++ = clp[384+((y2 - c2 - c3)>>16)];
*d2++ = clp[384+((y2 + c4)>>16)];
}
d1 += 3*width;
d2 += 3*width;
py1+= width;
py2+= width;
}


}

/****************************************************/
/* Sum the input */
/* Input: input, len */
/* Output: input */
/* Algorithm: add */
/****************************************************/
void InitConvtTbl()
{
long int crv,cbu,cgu,cgv;
int i,ind;

crv = 104597; cbu = 132201; /* fra matrise i global.h */
cgu = 25675; cgv = 53279;

for (i = 0; i < 256; i++) {
crv_tab = (i-128) * crv;
cbu_tab = (i-128) * cbu;
cgu_tab = (i-128) * cgu;
cgv_tab = (i-128) * cgv;
tab_76309 = 76309*(i-16);
}

for (i=0; i<384; i++)
clp =0;
ind=384;
for (i=0;i<256; i++)
clp[ind++]=i;
ind=640;
for (i=0;i<384;i++)
clp[ind++]=255;
}　　　　　　

你用的什么方法才采集的？
read还是mmap？
交流一下？
我用mmap方法采集的，村到1.bmp文件，结果文件打开后什么都没有。