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我是新来的这个东西,但我需要从jpeg使用jpeg库得到dc系数? 我被告知提示相应的函数在jdhuff.c中,但我找不到它。我试图找到一个关于jpg库的体面的文章,我可以得到它,但迄今为止没有成功。如何使用jpg库从jpg获取DC系数?
所以我希望你们能够帮助我一点,并指出我有些文件或有提示。 所以,这里是我所知道的:
jpg图片由8x8块组成。那是64像素。其中63个被命名为AC,1个被命名为DC。这就是系数。位置在数组[0] [0]处。
但我该如何阅读与JPG图书馆?我正在使用C++。
编辑: 这是我到目前为止有:
read_jpeg::read_jpeg(const std::string& filename)
{
FILE* fp = NULL; // File-Pointer
jpeg_decompress_struct cinfo; // jpeg decompression parameters
JSAMPARRAY buffer; // Output row-buffer
int row_stride = 0; // physical row width
my_error_mgr jerr; // Custom Error Manager
// Set Error Manager
cinfo.err = jpeg_std_error(&jerr.pub);
jerr.pub.error_exit = my_error_exit;
// Handle longjump
if (setjmp(jerr.setjmp_buffer)) {
// JPEG has signaled an error. Clean up and throw an exception.
jpeg_destroy_decompress(&cinfo);
fclose(fp);
throw std::runtime_error("Error: jpeg has reported an error.");
}
// Open the file
if ((fp = fopen(filename.c_str(), "rb")) == NULL)
{
std::stringstream ss;
ss << "Error: Cannot read '" << filename.c_str() << "' from the specified location!";
throw std::runtime_error(ss.str());
}
// Initialize jpeg decompression
jpeg_create_decompress(&cinfo);
// Show jpeg where to read the data
jpeg_stdio_src(&cinfo, fp);
// Read the header
jpeg_read_header(&cinfo, TRUE);
// Decompress the file
jpeg_start_decompress(&cinfo);
// JSAMPLEs per row in output buffer
row_stride = cinfo.output_width * cinfo.output_components;
// Make a one-row-high sample array
buffer = (*cinfo.mem->alloc_sarray)((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);
// Read image using jpgs counter
while (cinfo.output_scanline < cinfo.output_height)
{
// Read the image
jpeg_read_scanlines(&cinfo, buffer, 1);
}
// Finish the decompress
jpeg_finish_decompress(&cinfo);
// Release memory
jpeg_destroy_decompress(&cinfo);
// Close the file
fclose(fp);
}