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Process spatial operations without ‘for’ loops in MATLAB

While working on some image enhancement applications which the intensity of a given pixel is also a function of its location (spatial coordinates), I used to use ‘for’ loops to iterate each pixel at once and calculate its intensity based on (x,y) value obtained from those two ‘for’ loops. This is very annoying since it takes quite some time to process two ‘for’ loops as well as it is a belief that the MATLAB ‘for’ loops are used to slow. In this article I share my experience how I avoided the requirement of two ‘for’ loops by using the properties of complex numbers for a photo effect which I described in a previous article of mine.

Normally in an image there is an mxnx3 matrix which represents red, green and blue intensities respectively. In my case I append another 4th matrix of coordinates which makes the image matrix as mxnx4. (Even-though there is a memory drawback in this design, it is very easy to handle rather than two nested ‘for’ loops).

This 4th matrix contains complex numbers which their real value is equal to row index and its imaginary value is equal to its column index. And now we do have another advantage. Using the properties of complex numbers we can easily calculate the distance and angle between two pixels in interest which is very useful in image effects such as ‘focal BW’.

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2013 October 18 Posted by | Image Processing, MATLAB | , , , , | 1 Comment


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