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POWebP encoding - Segmentation Fault
 

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  1. POWebP encoding - Segmentation Fault
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    <p>So I'm trying to use the webp API to encode images. Right now I'm going to be using openCV to open and manipulate the images, then I want to save them off as webp. Here's the source I'm using:</p> <pre><code>#include &lt;stdlib.h&gt; #include &lt;stdio.h&gt; #include &lt;math.h&gt; #include &lt;cv.h&gt; #include &lt;highgui.h&gt; #include &lt;webp/encode.h&gt; int main(int argc, char *argv[]) { IplImage* img = 0; int height,width,step,channels; uchar *data; int i,j,k; if (argc&lt;2) { printf("Usage:main &lt;image-file-name&gt;\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-&gt;height; width = img-&gt;width; step = img-&gt;widthStep; channels = img-&gt;nChannels; data = (uchar *)img-&gt;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&lt;height;i++) { for (j=0;j&lt;width;j++) { for (k=0;k&lt;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(&amp;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); } </code></pre> <p>When I execute this, I get this:</p> <pre><code>nato@ubuntu:~/webp/webp_test$ ./helloWorld ~/Pictures/mars_sunrise.jpg processing a 2486x1914 image with 3 channels encoding image Segmentation fault </code></pre> <p>It displays the image just fine, but segfaults on the encoding. My initial guess was that it's because I'm releasing the img before I try to write out the data, but it doesn't seem to matter whether I release it before or after I try the encoding. Is there something else I'm missing that might cause this problem? Do I have to make a copy of the image data or something?</p> <p>The WebP api docs are... sparse. Here's what the README says about WebPEncodeRGB:</p> <pre><code>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); </code></pre> <p>The docs specifically do not say what the 'stride' is, but I'm assuming that it's the same as the 'step' from opencv. Is that reasonable? </p> <p>Thanks in advance!</p>
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