使用libjpeg-turbo的TurboJPEG的示例或教程

Question

libjpeg-turbo的说明在此描述了TurboJPEG API:"此API包装了libjpeg-turbo,并提供了一个易于使用的界面,用于压缩和解压缩内存中的JPEG图像".很好,但有一些使用此API的可靠实例吗？只是想在内存中解压缩一个相当香草的jpeg.

我找到了一些比如https://github.com/erlyvideo/jpeg/blob/master/c_src/jpeg.c,它似乎使用的是TurboJPEG API,但还有更多可靠/多变的例子吗？

libjpeg-turbo的来源已有详细记录,因此确实有帮助.

Answer 1

好的,我知道你已经解决了你的问题,但有些人,就像我一样,可能会搜索一些简单的例子,我会分享我创建的内容.这是一个压缩和解压缩RGB图像的例子.否则我认为TurboJPEG的API文档很容易理解!

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,您将在_compressedImage中获得压缩图像.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);

一些随意的想法:

我刚回来在这个当我写我的学士论文,我注意到,如果你在一个循环中运行压缩最好是存储JPEG缓冲的最大尺寸不必分配一个新动不动.基本上,而不是做:

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,保持已分配内存的大小,long unsigned int _jpegBufferSize = 0;在每次压缩循环之前,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;

在压缩之后,可以将内存大小与实际的jpegSize进行比较,如果它高于先前的内存大小,则将其设置为jpegSize.

Answer 2

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，它是独立的，可以初始化一个虚拟图像并将编码的图像输出到本地文件。

下面的代码不是我自己的，归功于https://sourceforge.net/p/libjpeg-turbo/discussion/1086868/thread/e402d36f/#8722。再次将它张贴在这里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;
}

Answer 3

最后，我使用了在互联网上找到的随机代码（例如https://github.com/erlyvideo/jpeg/blob/master/c_src/jpeg.c）以及 libjeg-turbo 的 .c 和头文件的组合，这些都是有据可查的。 这个官方 API 也是一个很好的信息源。