通过libjpeg-turbo实现对jpeg图像的解码

╰半夏微凉° 2023-06-12 04:20 7阅读 0赞

之前在[https://blog.csdn.net/fengbingchun/article/details/89715416][https_blog.csdn.net_fengbingchun_article_details_89715416]中介绍过通过libjpeg-turbo接口实现将数据编码或压缩成jpeg数据并通过FILE的fwrite接口将其直接保存成\*.jpg图像，当时用的是libjpeg的接口，其实还可以使用turbojpeg api的接口即tjCompress2实现对数据的编码，见下面的code：

int get_jpeg_compress_data2(const unsigned char* data, int width, int height, int pixelFormat, unsigned char** jpegBuf, unsigned long* jpegSize, int jpegSubsamp, int jpegQual, int flags)
    {
    	tjhandle handle = tjInitCompress();
    	int ret = tjCompress2(handle, data, width, 0, height, pixelFormat, jpegBuf, jpegSize, jpegSubsamp, jpegQual, flags);
    	tjDestroy(handle);
    
    	return 0;
    }

相对应的实现图像的解码或解压缩也有两套接口，一套是libjpeg的，即头文件为jpeglib.h，一套是turbojpeg的，即头文件为turbojpeg.h。测试代码如下：

#include <string>
    #include <memory>
    
    #include "funset.hpp"
    #include <opencv2/opencv.hpp>
    
    int test_libjpeg_turbo_decompress()
    {
    #ifdef _MSC_VER
    	std::string image_path{ "E:/GitCode/OCR_Test/test_data/" };
    #else
    	std::string image_path{ "test_data/" };
    #endif
    
    	std::string image_name = image_path + "tirg.jpg";
    
    	int width, height, channels;
    	long long t1 = Timer::getNowTime();
    	std::unique_ptr<unsigned char[]> data = get_jpeg_decompress_data(image_name.c_str(), width, height, channels);
    	long long t2 = Timer::getNowTime();
    	if (data == nullptr) {
    		fprintf(stderr, "fail to decompress: %s\n", image_name.c_str());
    		return -1;
    	}
    
    	fprintf(stdout, "decompress time 1: %lldms, width: %d, height: %d, channels: %d\n", t2 - t1, width, height, channels);
    	std::string result_image = image_path + "result_tirg.png";
    	cv::Mat mat(height, width, CV_8UC3, data.get());
    	cv::cvtColor(mat, mat, CV_RGB2BGR);
    	cv::imwrite(result_image, mat); // save *.jpg will crash in linux
    
    	int width2, height2, channels2;
    	t1 = Timer::getNowTime();
    	std::unique_ptr<unsigned char[]> data2 = get_jpeg_decompress_data2(image_name.c_str(), width2, height2, channels2);
    	t2 = Timer::getNowTime();
    	if (data2 == nullptr) {
    		fprintf(stderr, "fail to decompress: %s\n", image_name.c_str());
    		return -1;
    	}
    
    	fprintf(stdout, "decompress time 2: %lldms, width2: %d, height2: %d, channels2: %d\n", t2 - t1, width2, height2, channels2);
    	std::string result_image2 = image_path + "result_tirg2.png";
    	cv::Mat mat2(height2, width2, CV_8UC3, data2.get());
    	cv::cvtColor(mat2, mat2, CV_RGB2BGR);
    	cv::imwrite(result_image2, mat2);
    
    	return 0;
    }
    
    std::unique_ptr<unsigned char[]> get_jpeg_decompress_data2(const char* image_name, int& width, int& height, int& channels)
    {
    	FILE* infile = fopen(image_name, "rb");
    	if (infile == nullptr) {
    		fprintf(stderr, "can't open %s\n", image_name);
    		return nullptr;
    	}
    
    	fseek(infile, 0, SEEK_END);
    	unsigned long srcSize = ftell(infile);
    	std::unique_ptr<unsigned char[]> srcBuf(new unsigned char[srcSize]);
    	fseek(infile, 0, SEEK_SET);
    	fread(srcBuf.get(), srcSize, 1, infile);
    	fclose(infile);
    
    	tjhandle handle = tjInitDecompress();
    	int subsamp, cs;
    	int ret = tjDecompressHeader3(handle, srcBuf.get(), srcSize, &width, &height, &subsamp, &cs);
    	if (cs == TJCS_GRAY) channels = 1;
    	else channels = 3;
    
    	int pf = TJCS_RGB;
    	int ps = tjPixelSize[pf];
    	std::unique_ptr<unsigned char[]> data(new unsigned char[width * height * channels]);
    	ret = tjDecompress2(handle, srcBuf.get(), srcSize, data.get(), width, width * channels, height, TJPF_RGB, TJFLAG_NOREALLOC);
    
    	tjDestroy(handle);
    
    	return data;
    }
    
    std::unique_ptr<unsigned char[]> get_jpeg_decompress_data(const char* image_name, int& width, int& height, int& channels)
    {
    	FILE* infile = fopen(image_name, "rb");
    	if (infile == nullptr) {
    		fprintf(stderr, "can't open %s\n", image_name);
    		return nullptr;
    	}
    
    	struct jpeg_decompress_struct cinfo;
    	struct jpeg_error_mgr jerr;
    
    	/* Step 1: allocate and initialize JPEG decompression object */
    	cinfo.err = jpeg_std_error(&jerr);
    	jpeg_create_decompress(&cinfo);
    	/* Step 2: specify data source (eg, a file) */
    	jpeg_stdio_src(&cinfo, infile);
    	/* Step 3: read file parameters with jpeg_read_header() */
    	jpeg_read_header(&cinfo, TRUE);
    	/* Step 4: set parameters for decompression */
    	/* Step 5: Start decompressor */
    	jpeg_start_decompress(&cinfo);
    
    	cinfo.out_color_space = JCS_RGB; //JCS_EXT_BGR;
    
    	int row_stride = cinfo.output_width * cinfo.output_components;
    	/* Output row buffer */
    	JSAMPARRAY buffer = (*cinfo.mem->alloc_sarray)((j_common_ptr)&cinfo, JPOOL_IMAGE, row_stride, 1);
    
    	width = cinfo.output_width;
    	height = cinfo.output_height;
    	channels = cinfo.output_components;
    	std::unique_ptr<unsigned char[]> data(new unsigned char[width * height * channels]);
    
    	/* Step 6: while (scan lines remain to be read) */
    	for (int j = 0; j < cinfo.output_height; ++j) {
    		jpeg_read_scanlines(&cinfo, buffer, 1);
    		unsigned char* p = data.get() + j * row_stride;
    		memcpy(p, buffer[0], row_stride);
    	}
    
    	/* Step 7: Finish decompression */
    	jpeg_finish_decompress(&cinfo);
    	/* Step 8: Release JPEG decompression object */
    	jpeg_destroy_decompress(&cinfo);
    	fclose(infile);
    
    	return data;
    }

执行结果如下：对于小图来说，两套接口执行时间上差不多，对于400\*330\*3的图像，两种方式都大约在3ms至5ms之间；对于大图来说，反复测试多次，大多数turbojpeg.h的接口要比jpeglib.h的接口耗时更少一些。而且turbojpeg.h的实现要不jpeglib.h代码量更少一些。因此推荐直接使用turbojpeg.h中的接口。

![20191031142720177.png][]

**GitHub**：[https://github.com//fengbingchun/OCR\_Test][https_github.com_fengbingchun_OCR_Test]

[https_blog.csdn.net_fengbingchun_article_details_89715416]: https://blog.csdn.net/fengbingchun/article/details/89715416
[20191031142720177.png]: /images/20230531/f79fb9051563437ab5b5e81117d5b052.png
[https_github.com_fengbingchun_OCR_Test]: https://github.com//fengbingchun/OCR_Test