使用libjpeg-turbo的turbojpeg的示例或教程[英] Examples or tutorials of using libjpeg-turbo's TurboJPEG

问题描述

libjpeg-turbo的说明

我找到了一些部分，例如 .com/erlyvideo/jpeg/blob/master/c_src/jpeg.c 似乎正在使用turbojpeg API，但是还有更多固体/变化的示例吗?

libjpeg-turbo的来源有充分的记录，因此确实有帮助.

推荐答案

最后，我使用了在Internet上找到的随机代码的组合(例如 https://github.com/erlyvideo/jpeg/blob/master/c_src/jpeg.c )和.c and header Files for Libjeg-turbo，for Libjeg-turbo，已有文献记载. 其他推荐答案

好吧，我知道您确实已经解决了您的问题，但是作为某些人，就像我一样，可以搜索一些简单的例子，我将分享我的创建. 这是一个示例，正在压缩和解压缩RGB图像.否则，我认为 turbojpeg 的API文档非常容易理解！

压缩:

#include <turbojpeg.h>

const int JPEG_QUALITY = 75;
const int COLOR_COMPONENTS = 3;
int _width = 1920;
int _height = 1080;
long unsigned int _jpegSize = 0;
unsigned char* _compressedImage = NULL; //!< Memory is allocated by tjCompress2 if _jpegSize == 0
unsigned char buffer[_width*_height*COLOR_COMPONENTS]; //!< Contains the uncompressed image

tjhandle _jpegCompressor = tjInitCompress();

tjCompress2(_jpegCompressor, buffer, _width, 0, _height, TJPF_RGB,
          &_compressedImage, &_jpegSize, TJSAMP_444, JPEG_QUALITY,
          TJFLAG_FASTDCT);

tjDestroy(_jpegCompressor);

//to free the memory allocated by TurboJPEG (either by tjAlloc(), 
//or by the Compress/Decompress) after you are done working on it:
tjFree(&_compressedImage);

之后，您在_compressedimage中具有压缩图像. 要解压缩您必须执行以下操作:

减压:

#include <turbojpeg.h>

long unsigned int _jpegSize; //!< _jpegSize from above
unsigned char* _compressedImage; //!< _compressedImage from above

int jpegSubsamp, width, height;
unsigned char buffer[width*height*COLOR_COMPONENTS]; //!< will contain the decompressed image

tjhandle _jpegDecompressor = tjInitDecompress();

tjDecompressHeader2(_jpegDecompressor, _compressedImage, _jpegSize, &width, &height, &jpegSubsamp);

tjDecompress2(_jpegDecompressor, _compressedImage, _jpegSize, buffer, width, 0/*pitch*/, height, TJPF_RGB, TJFLAG_FASTDCT);

tjDestroy(_jpegDecompressor);

一些随机的想法:

我刚刚撰写学士学位论文时，我又回来了，我注意到，如果您在循环中运行压缩，则最好是存储JPEG缓冲区最大的尺寸，而不必分配新的尺寸转动.基本上，而不是这样做:

long unsigned int _jpegSize = 0;

tjCompress2(_jpegCompressor, buffer, _width, 0, _height, TJPF_RGB,
          &_compressedImage, &_jpegSize, TJSAMP_444, JPEG_QUALITY,
          TJFLAG_FASTDCT);

我们将添加一个对象变量，保留分配的内存long unsigned int _jpegBufferSize = 0;的大小，在每次压缩回合之前，我们将jpegsize设置回该值:

long unsigned int jpegSize = _jpegBufferSize;

tjCompress2(_jpegCompressor, buffer, _width, 0, _height, TJPF_RGB,
          &_compressedImage, &jpegSize, TJSAMP_444, JPEG_QUALITY,
          TJFLAG_FASTDCT);

_jpegBufferSize = _jpegBufferSize >= jpegSize? _jpegBufferSize : jpegSize;

压缩后，如果将内存大小与实际的jpegsize进行比较，并将其设置为jpegsize，如果它高于先前的内存大小.

其他推荐答案

我最终使用以下代码作为JPEG编码和解码的工作示例.我能找到的最好的例子是，它是独立的，可以初始化虚拟图像并将编码的图像输出到本地文件.

下面的代码是不是我自己的，荣誉转到 https://sourceforge.net/p/libjpeg-turbo/discussion/1086868/thread/e402d36f/#8722 .再次在这里发布它，以帮助任何人发现很难让Libjpeg Turbo工作.

#include "turbojpeg.h"
#include <iostream>
#include <string.h>
#include <errno.h>

using namespace std;

int main(void)
{
    unsigned char *srcBuf; //passed in as a param containing pixel data in RGB pixel interleaved format
    tjhandle handle = tjInitCompress();

    if(handle == NULL)
    {
        const char *err = (const char *) tjGetErrorStr();
        cerr << "TJ Error: " << err << " UNABLE TO INIT TJ Compressor Object\n";
        return -1;
    }
    int jpegQual =92;
    int width = 128;
    int height = 128;
    int nbands = 3;
    int flags = 0;
    unsigned char* jpegBuf = NULL;
    int pitch = width * nbands;
    int pixelFormat = TJPF_GRAY;
    int jpegSubsamp = TJSAMP_GRAY;
    if(nbands == 3)
    {
        pixelFormat = TJPF_RGB;
        jpegSubsamp = TJSAMP_411;
    }
    unsigned long jpegSize = 0;

    srcBuf = new unsigned char[width * height * nbands];
    for(int j = 0; j < height; j++)
    {
        for(int i = 0; i < width; i++)
        {
            srcBuf[(j * width + i) * nbands + 0] = (i) % 256;
            srcBuf[(j * width + i) * nbands + 1] = (j) % 256;
            srcBuf[(j * width + i) * nbands + 2] = (j + i) % 256;
        }
    }

    int tj_stat = tjCompress2( handle, srcBuf, width, pitch, height,
        pixelFormat, &(jpegBuf), &jpegSize, jpegSubsamp, jpegQual, flags);
    if(tj_stat != 0)
    {
        const char *err = (const char *) tjGetErrorStr();
        cerr << "TurboJPEG Error: " << err << " UNABLE TO COMPRESS JPEG IMAGE\n";
        tjDestroy(handle);
        handle = NULL;
        return -1;
    }

    FILE *file = fopen("out.jpg", "wb");
    if (!file) {
        cerr << "Could not open JPEG file: " << strerror(errno);
        return -1;
    }
    if (fwrite(jpegBuf, jpegSize, 1, file) < 1) {
        cerr << "Could not write JPEG file: " << strerror(errno);
        return -1;
    }
    fclose(file);

    //write out the compress date to the image file
    //cleanup
    int tjstat = tjDestroy(handle); //should deallocate data buffer
    handle = 0;
}

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