jpeglib库从内存地址读取数据解码。
最近做项目用到了jpeglib这个库做图像jpg图像的解码操作,需要从内存地址解码数据。看了网上的一些博客有的说是不能从内存读取解码,需要改写接口,但后来我在头文件里找了下,发现了其实并不像一些博主所说的没有。我找到了比如这个接口:jpeg_mem_src就支持从内存地址解码。为了让大家不要被误导,少走弯路,特写这个博客供大家参考。经过我些代码做验证完全没有问题。下面贴上代码供大家参考,如有问题,欢迎留言指正。
//jpeg 解压缩出错处理
struct my_error_mgr
{
struct jpeg_error_mgr pub;
jmp_buf setjmp_buffer;
};
typedef struct my_error_mgr* my_error_ptr;
//jpeg 解压缩错误处理函数
METHODDEF(void) my_error_exit(j_common_ptr cinfo)
{
my_error_ptr myerr = (my_error_ptr)cinfo->err;
(*cinfo->err->output_message) (cinfo);
longjmp(myerr->setjmp_buffer, 1);
}
typedef struct my_error_mgr* my_error_ptr;
JPG jpg_depress(unsigned char* jpg_buffer, int file_len)
{
struct jpeg_decompress_struct cinfo;
//struct jpeg_error_mgr jerr;
struct my_error_mgr jerr;
JSAMPARRAY buffer;
int row_width;
JPG jpg;
unsigned char* output_buffer;
unsigned char* tmp = NULL;
//cinfo.err = jpeg_std_error(&jerr);
cinfo.err = jpeg_std_error(&jerr.pub);
//错误处理
jerr.pub.error_exit = my_error_exit;
if (setjmp(jerr.setjmp_buffer))
{
//在正常情况下,setjmp将返回0,而如果程序出现错误,即调用my_error_exit
//然后程序将再次跳转于此,同时setjmp将返回在my_error_exit中由longjmp第二个参数设定的值1
//并执行以下代码
std::string error = std::string((char*)cinfo.err->output_message);
jpeg_destroy_decompress(&cinfo);
throw error;
}
// Initialization of JPEG compression objects
jpeg_create_decompress(&cinfo);
/* Specify data source for decompression */
jpeg_mem_src(&cinfo, jpg_buffer, file_len);
/* 1.设置读取jpg文件头部,Read file header, set default decompression parameters */
(void)jpeg_read_header(&cinfo, TRUE);
/* 2.开始数据 Start decompressor */
//解压缩
(void)jpeg_start_decompress(&cinfo);
row_width = cinfo.output_width * cinfo.output_components;
//不是彩色图 先不处理
if (cinfo.num_components != 3) {
//throw std::string("cinfo imput image is not 3 channels.");
throw invalid_argument("jpeglib cinfo input image is not 3 channels.");
}
jpg.w = cinfo.output_width;
jpg.h = cinfo.output_height;
/* *_width = cinfo.output_width;
*_hight = cinfo.output_height;
*_line_width = row_width;*/
/* 3.跳过读取的头文件字节Make a one-row-high sample array that will go away when done with image */
buffer = (*cinfo.mem->alloc_sarray)
((j_common_ptr)&cinfo, JPOOL_IMAGE, row_width, 1);
//write_bmp_header(&cinfo, output_file);
int size = row_width * cinfo.output_height;
output_buffer = (unsigned char*)malloc(size);
//output_buffer = gImageBuffer;
jpg.data = output_buffer;
//memset(output_buffer, 0, size);
tmp = output_buffer;
//*_output_buffer = output_buffer;
//UINT8* data = output_buffer;
/* 4.Process data由左上角从上到下行行扫描 */
while (cinfo.output_scanline < cinfo.output_height) {
(void)jpeg_read_scanlines(&cinfo, buffer, 1);
memcpy(tmp, *buffer, row_width);
tmp += row_width;
}
(void)jpeg_finish_decompress(&cinfo);
jpeg_destroy_decompress(&cinfo);
/* Close files, if we opened them */
return jpg;
}