pixel data from mex to matlab: mxArray definition..

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Enrico Boscolo 2015-6-29

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https://ww2.mathworks.cn/matlabcentral/answers/225725-pixel-data-from-mex-to-matlab-mxarray-definition

评论： Enrico Boscolo 2015-7-2

Hello I’m trying to use TCP/IP gEth. camera using mex file. The cpp code provides by camera vendor is very useful to open library/open/close camera and trigger, also I’m able to save image bmp in a selected folder from where I can read the image (1600X1200) from matlab (imread/imshow). Everything works fine but I’m not able to transfer the pixel data from mex to matlab. Below an example of the cpp code where a simple pixel calculation is performed (*pPixel = ~*pPixel): // get the pointer to the image data

    void* pData = NULL;
    int32_t iImageOffset = 0;
    pBuffer->GetPtr (LvBuffer_UniBase, &pData);
    pBuffer->GetInt32 (LvBuffer_UniImageOffset, &iImageOffset);
    pData = (uint8_t*)pData + iImageOffset;
  for (int32_t j=0; j<(1200); j++)
        {
            uint8_t* pPixel = ((uint8_t*)pData) +  j*1600;
            for (int32_t i=0; i<(1600); i++)
            {
                for (int32_t k=0; k<iBytesPerPixel; k++)
                {
        *pPixel = ~*pPixel;
                    pPixel++;
                }
            }
      }

My problem is how to transfer the pPixel (uint_8) to matlab… I’m tring to use mxArray B; B= mxCreateNumericData(1600, 1200, mxINT8_CLASS, mxREAL); But I don’t know how to populate the matrix B. Please, any advices??

M. Thanks

Enrico

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Answer 1

Titus Edelhofer 2015-6-29

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https://ww2.mathworks.cn/matlabcentral/answers/225725-pixel-data-from-mex-to-matlab-mxarray-definition#answer_184364

编辑：Titus Edelhofer 2015-6-30

在 MATLAB Online 中打开

Hi Enrico,

as a .bmp it probably has 24 bits, i.e., you iBytesPerPixel is 3. Therefore you should allocate a 1600x1200x3 matrix:

mwSize aSize[3] = {1600, 1200, 3};
plhs[0] = mxCreateNumericArray(3, aSize, mxUINT8_CLASS, mxREAL);
uint8_t *pData = (uint8_t*) mxGetData(plhs[0]);

You might use the code you have above to loop on the indices, and put each pixel from pPixel into pData. Note though, that the indices are running differently in MATLAB then in your code, it should be something like

pData[k*1200*1600 + j*1600 + i] = *pPixel;

but I'm not 100% sure I admit ;-).

Titus