我发现了这个使用 libjpeg 写入文件的函数:
int write_jpeg_file( char *filename )
{
struct jpeg_compress_struct cinfo;
struct jpeg_error_mgr jerr;
/* this is a pointer to one row of image data */
JSAMPROW row_pointer[1];
FILE *outfile = fopen( filename, "wb" );
if ( !outfile )
{
printf("Error opening output jpeg file %s\n!", filename );
return -1;
}
cinfo.err = jpeg_std_error( &jerr );
jpeg_create_compress(&cinfo);
jpeg_stdio_dest(&cinfo, outfile);
/* Setting the parameters of the output file here */
cinfo.image_width = width;
cinfo.image_height = height;
cinfo.input_components = bytes_per_pixel;
cinfo.in_color_space = color_space;
/* default compression parameters, we shouldn't be worried about these */
jpeg_set_defaults( &cinfo );
/* Now do the compression .. */
jpeg_start_compress( &cinfo, TRUE );
/* like reading a file, this time write one row at a time */
while( cinfo.next_scanline < cinfo.image_height )
{
row_pointer[0] = &raw_image[ cinfo.next_scanline * cinfo.image_width * cinfo.input_components];
jpeg_write_scanlines( &cinfo, row_pointer, 1 );
}
/* similar to read file, clean up after we're done compressing */
jpeg_finish_compress( &cinfo );
jpeg_destroy_compress( &cinfo );
fclose( outfile );
/* success code is 1! */
return 1;
}
我实际上需要将 jpeg 压缩图像写入内存缓冲区,而不将其保存到文件中,以节省时间。有人可以举个例子吗?
我已经在网上搜索了一段时间,但是如果有的话,文档非常稀少,而且示例也很难找到。
最佳答案
您可以很容易地定义自己的目的地管理器。 jpeg_compress_struct
包含指向 jpeg_destination_mgr
的指针,其中包含指向缓冲区的指针、缓冲区中剩余空间的计数和 3 个函数指针:
init_destination (j_compress_ptr cinfo)
empty_output_buffer (j_compress_ptr cinfo)
term_destination (j_compress_ptr cinfo)
在第一次调用 jpeg 库之前,您需要填写函数指针,并让这些函数处理缓冲区。如果您创建的缓冲区大于您期望的最大可能输出,这将变得微不足道; init_destination
只是填写缓冲区指针和计数,empty_output_buffer
和 term_destination
什么都不做。
这里有一些示例代码:
std::vector<JOCTET> my_buffer;
#define BLOCK_SIZE 16384
void my_init_destination(j_compress_ptr cinfo)
{
my_buffer.resize(BLOCK_SIZE);
cinfo->dest->next_output_byte = &my_buffer[0];
cinfo->dest->free_in_buffer = my_buffer.size();
}
boolean my_empty_output_buffer(j_compress_ptr cinfo)
{
size_t oldsize = my_buffer.size();
my_buffer.resize(oldsize + BLOCK_SIZE);
cinfo->dest->next_output_byte = &my_buffer[oldsize];
cinfo->dest->free_in_buffer = my_buffer.size() - oldsize;
return true;
}
void my_term_destination(j_compress_ptr cinfo)
{
my_buffer.resize(my_buffer.size() - cinfo->dest->free_in_buffer);
}
cinfo->dest->init_destination = &my_init_destination;
cinfo->dest->empty_output_buffer = &my_empty_output_buffer;
cinfo->dest->term_destination = &my_term_destination;
关于c++ - 使用libjpeg写入内存缓冲区而不是文件?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/4559648/