trouble passing image from c to matlab..

...
mxArray *mat1;
UINT8_T *dynamicData;    
mwSize index;
unsigned long int elements;

elements = (ImgTempTp->width)*(ImgTempTp->height);    
dynamicData = mxCalloc(elements, sizeof(UINT8_T));
for ( index = 0; index < elements; index++ ) {
        dynamicData[index] = ImgTempTp->imageData[index];
    }
mat1 = mxCreateNumericMatrix(0, 0, mxUINT8_CLASS, mxREAL);
mxSetData(mat1, dynamicData);
mxSetM(mat1, ImgTempTp->height);
mxSetN(mat1, ImgTempTp->width);
mlfShowimage(mat1);
.
.

ImgTempTp is an image created by opencv. the data type is unsigned char.

function [] = showimage(img)
figure,imshow(img);
input('Press Enter to continue...');
end

Some times the image appears properly but many times it gets mixed up in 2-3 manners i.e. it has 2-3 sections which contains parts of original image in tilted fashion

I have tried memcpy also. But i get the same error.. PLs help...

[Vikash Anand]

If i try loading an image using cvLoadImage in opencv and then pass it to matlab, i get different images at each run.

Also, the distorted image has max. no. of sections as 4.

[Vikash Anand]

result :

https://sites.google.com/site/scrapfromvks/matlab

these images have been captured by opencv haar detect and passed on to matlab.. Opencv displays all of these correctly.

Answer 1

[Kaustubha Govind]

Is there a reason your are using a rather roundabout way to achieve this? Why not use something like:

...
mxArray *mat1;
UINT8_T *dynamicData;    
mwSize index;
unsigned long int elements;

elements = (ImgTempTp->width)*(ImgTempTp->height); 

mat1 = mxCreateNumericMatrix(ImgTempTp->height, ImgTempTp->width, mxUINT8_CLASS, mxREAL);
dynamicData = (UINT8_T *)mxGetData(mat1);
for ( index = 0; index < elements; index++ ) {
        dynamicData[index] = ImgTempTp->imageData[index];
}

mlfShowimage(mat1);
.
.

Do you know if ImgTempTp->imageData contains the image in the right indexing order? It seems like the image is being read along the diagonal. Have you tried examining the contents of ImgTempTp->imageData and comparing them with the value 'img' that's passed into showimage?

[Vikash Anand]

Thanx for your reply, but this too didn't work... :( ..

the images i have uploaded seem to have a pattern in error : proper image/3 sections for images with "even" dimensions and 2/4 sections for "odd" dimensions.

Amazingly, if i create an opencv structure and copy the data from "mat1" to it, opencv displays it properly ..

unsigned char *dest,*src;

IplImage*ImgTest = cvCreateImage(cvSize(ImgTemp->height,ImgTemp->width),IPL_DEPTH_8U,1); /*dimensions of temp interchanged for transposing*/

bytescount = (ImgTempTp->width)*(ImgTempTp->height)*sizeof(char)

src = (unsigned char *)mxGetPr(mat1);

dest = (uchar *)(ImgTest->imageData);

for(j=0;j< bytescount;j++)

{

dest[j] = src[j];

}

cvShowImage("EBGM Debug",ImgTempTp);

cvWaitKey(2000);

ignore the transpose...

[Vikash Anand]

The first round about manner i found in "arrayFillSetData.c" in matlab examples.. so just followed it.

Before that, i also tried:

mxArray *mat1;

mwSize dims[2];

dims[0] = (mwSize)(ImgTempTp->width);

dims[1] = (mwSize)(ImgTempTp->height);

mat1 = mxCreateNumericArray(2,dims,mxUINT8_CLASS,mxREAL);

memcpy(mxGetPr(mat1), (uchar *)(ImgTempTp->imageData), (ImgTempTp->width)*(ImgTempTp->height)*sizeof(char));

mlfShowimage(mat1);

but none of these worked !! :(

[Kaustubha Govind]

Could it be than opencv is somehow not storing the pixel values in the expected linear order?

Answer 2

[Vikash Anand]

Hey govinda.. i found the solution .. It is something related to 4 bytes alignment. I resized the image in opencv before transferring to matlab such that the dimensions were multiple of 4 and it worked perfectly !!! :)