WebP编码 - 分段错误

Question

所以我正在尝试使用webp API来编码图像.现在我将使用openCV来打开和操作图像,然后我想将它们保存为webp.这是我正在使用的来源:

#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <cv.h>
#include <highgui.h>
#include <webp/encode.h>

int main(int argc, char *argv[])
{

    IplImage* img = 0;
    int height,width,step,channels;
    uchar *data;
    int i,j,k;
    if (argc<2) {
        printf("Usage:main <image-file-name>\n\7");
    exit(0);
    }
    // load an image
    img=cvLoadImage(argv[1]);

    if(!img){
        printf("could not load image file: %s\n",argv[1]);
        exit(0);
    }

    // get the image data
    height      = img->height;
    width       = img->width;
    step        = img->widthStep;
    channels    = img->nChannels;
    data        = (uchar *)img->imageData;
    printf("processing a %dx%d image with %d channels \n", width, height, channels);

    // create a window
    cvNamedWindow("mainWin", CV_WINDOW_AUTOSIZE);
    cvMoveWindow("mainWin",100,100);

    // invert the image
    for (i=0;i<height;i++) {
        for (j=0;j<width;j++) {
            for (k=0;k<channels;k++) {
                data[i*step+j*channels+k] = 255-data[i*step+j*channels+k];
            }
        }
    }

    // show the image
    cvShowImage("mainWin", img);

    // wait for a key
    cvWaitKey(0);
    // release the image
    cvReleaseImage(&img);

    float qualityFactor = .9;
    uint8_t** output;
    FILE *opFile;
    size_t datasize;
    printf("encoding image\n");
    datasize = WebPEncodeRGB((uint8_t*)data,width,height,step,qualityFactor,output);

    printf("writing file out\n");
    opFile=fopen("output.webp","w");
    fwrite(output,1,(int)datasize,opFile);
}

当我执行此操作时,我得到了这个:

nato@ubuntu:~/webp/webp_test$ ./helloWorld ~/Pictures/mars_sunrise.jpg 
processing a 2486x1914 image with 3 channels 
encoding image
Segmentation fault

它显示图像很好,但在编码上有段错误.我最初的猜测是因为我在尝试写出数据之前发布了img,但是在尝试编码之前或之后我是否发布它并不重要.还有其他我想念的东西可能导致这个问题吗？我是否必须复制图像数据或其他内容？

WebP api文档是......稀疏的.这是README关于WebPEncodeRGB的内容:

The main encoding functions are available in the header src/webp/encode.h
The ready-to-use ones are:

size_t WebPEncodeRGB(const uint8_t* rgb, int width, int height, 
    int stride, float quality_factor, uint8_t** output);

文档特别没有说'stride'是什么,但我假设它与opencv中的'step'相同.这合理吗？

提前致谢!

Answer 1

首先,如果以后使用它,请不要释放图像.其次,输出参数指向非初始化地址.这是如何使用初始化内存作为输出地址:

uint8_t* output;
datasize = WebPEncodeRGB((uint8_t*)data, width, height, step, qualityFactor, &output);