转：利用V4L2获取一张jpeg格式的图片
关于图片压缩和解压缩的内容：http://www.vckbase.com/index.php/wv/1488
1 YUV转RGB
static void YUV422toRGB888(int width, int height, unsigned char *src, unsigned char *dst)
{
int line, column;
unsigned char *py, *pu, *pv;
unsigned char *tmp = dst;
py = src;
pu = src + 1;
pv = src + 3;
#define CLIP(x) ( (x)>=0xFF ?
0xFF : ( (x) <= 0x00 ? 0x00 : (x) ) )
for (line = 0; line < height;
++line) {
for (column
= 0; column < width; ++column) {
*tmp++ = CLIP((double)*py + 1.402*((double)*pv-128.0));
*tmp++ = CLIP((double)*py - 0.344*((double)*pu-128.0) -
0.714*((double)*pv-128.0));
*tmp++ = CLIP((double)*py + 1.772*((double)*pu-128.0));
py += 2;
if ((column & 1)==1) {
pu += 4;
pv += 4;
}
}
}
}
2 压缩图片
static void process_image(const void * p, int len) {
// static char[115200] Outbuff ;
if (len > 0) {
unsigned char* src = (unsigned char*)p;
unsigned char* dst = malloc(width*height*3*sizeof(char));
YUV422toRGB888(width,height,src,dst);
write_jpeg("./pic001.jpg",dst,100,width, height, 0);
}
fflush(stdout);
}
int write_jpeg(char *filename,unsigned char *buf,int quality,int width, int height, int gray)
{
struct jpeg_compress_struct cinfo;
struct jpeg_error_mgr jerr;
FILE *fp;
int i;
unsigned char *line;
int line_length;
if (NULL == (fp = fopen(filename,"w")))
{
fprintf(stderr,"grab: can't open %s: %s\n",filename,strerror(errno));
return -1;
}
cinfo.err = jpeg_std_error(&jerr);
jpeg_create_compress(&cinfo);
jpeg_stdio_dest(&cinfo, fp);
cinfo.image_width = width;
cinfo.image_height = height;
cinfo.input_components = gray ? 1: 3;
cinfo.in_color_space = gray ? JCS_GRAYSCALE: JCS_RGB;
jpeg_set_defaults(&cinfo);
jpeg_set_quality(&cinfo, quality, TRUE);
jpeg_start_compress(&cinfo, TRUE);
line_length = gray ? width : width * 3;
for (i = 0, line = buf; i < height; i++, line += line_length)
jpeg_write_scanlines(&cinfo, &line, 1);
jpeg_finish_compress(&(cinfo));
jpeg_destroy_compress(&(cinfo));
fclose(fp);
return 0;
}
3 //摄像头采集帧图像的YUYV格式转换为JPEG格式
int compress_yuyv_to_jpeg(unsigned char *buf, unsigned char *buffer, int size, int quality) {
struct jpeg_compress_struct cinfo;
struct jpeg_error_mgr jerr;
JSAMPROW row_pointer[1];
unsigned char *line_buffer, *yuyv;
int z;
static int written;
//int count = 0;
//printf("%s\n", buf);
line_buffer = calloc (WIDTH * 3, 1);
yuyv = buf;//将YUYV格式的图片数据赋给YUYV指针
printf("compress start...\n");
cinfo.err = jpeg_std_error (&jerr);
jpeg_create_compress (&cinfo);
/* jpeg_stdio_dest (&cinfo, file); */
dest_buffer(&cinfo, buffer, size, &written);
cinfo.image_width = WIDTH;
cinfo.image_height = HEIGHT;
cinfo.input_components = 3;
cinfo.in_color_space = JCS_RGB;
jpeg_set_defaults (&cinfo);
jpeg_set_quality (&cinfo, quality, TRUE);
jpeg_start_compress (&cinfo, TRUE);
z = 0;
while (cinfo.next_scanline < HEIGHT) {
int x;
unsigned char *ptr = line_buffer;
for (x = 0; x < WIDTH; x++) {
int r, g, b;
int y, u, v;
if (!z)
y = yuyv[0] << 8;
else
y = yuyv[2] << 8;
u = yuyv[1] - 128;
v = yuyv[3] - 128;
r = (y + (359 * v)) >> 8;
g = (y - (88 * u) - (183 * v)) >> 8;
b = (y + (454 * u)) >> 8;
*(ptr++) = (r > 255) ? 255 : ((r < 0) ? 0 : r);
*(ptr++) = (g > 255) ? 255 : ((g < 0) ? 0 : g);
*(ptr++) = (b > 255) ? 255 : ((b < 0) ? 0 : b);
if (z++) {
z = 0;
yuyv += 4;
}
}
row_pointer[0] = line_buffer;
jpeg_write_scanlines (&cinfo, row_pointer, 1);
}
jpeg_finish_compress (&cinfo);
jpeg_destroy_compress (&cinfo);
free (line_buffer);
return (written);
}
