Increasing luminosity does not produce desired effect

    cvCvtColor(img,dst,CV_RGB2YCrCb);
    for  (int col=0;col<dst->width;col++) 
    { 
        for (int row=0;row<dst->height;row++) 
        { 
            int idxF = row*dst->widthStep + dst->nChannels*col; // Read the image data 
            CvPoint pt = {row,col};
            temp_ptr2[0] += temp_ptr1[0]* 0.0722 + temp_ptr1[1] * 0.7152 +temp_ptr1[2] *0.2126  ;   // channel Y 
        }
    }

But the result is this:

enter image description here

Please assist where am i going wrong?

Solution

There is a lot to say about this code sample:

First, you are using the old C-style API (IplImage pointers, cvBlah functions, etc), which is obsolete and more difficult to maintain (in particular, memory leaks are introduced easily), so you should consider using the C++-style structures and functions (cv::Mat structure and cv::blah functions).
Your error is probably coming from the instruction cvCopy(dst,img); at the very beginning. This fills your input image with nothing just before you start your processing, so you should remove this line.
For maximum speed, you should invert the two loops, so that you first iterate over rows then over columns. This is because images in OpenCV are stored row-by-row in memory, hence accessing the images by increasing column is more efficient with respect to the cache usage.
The temporary variable idxF is never used, so you should probably remove the following line too:
```
int idxF = row*dst->widthStep + dst->nChannels*col;
```
When you access image data to store the pixels in temp_ptr1 and temp_ptr2, you swapped the positions of the x and y coordinates. You should access the image in the following way:
```
temp_ptr1  = &((uchar*)(img->imageData + (img->widthStep*pt.y)))[pt.x*3];
```
You never release the memory allocated for dst, hence introducing a memory leak in your application. Call cvReleaseImage(&dst); at the end of your function.