Steve on Image Processing

Looking around the File Exchange 1

Posted by Steve Eddins,

Looking around the File Exchange Today I looked around the File Exchange for recent image processing submissions or updates. (You can do this yourself by searching using the tag image processing.) Here are a few things that caught my eye.getTimeStamp, by Christopher MacMinn, is an example of someone using the recently introduced linking between the... read more >>

Starting a Radon transform visualizer 3

Posted by Steve Eddins,

Starting a Radon transform visualizer  Today I set out to write a post called "Radon transform - under the hood."Things didn't turn out the way I expected.When I considered how to write the post I originally intended, I started thinking about how it would be nice to have a good way to visualize (and therefore... read more >>

Under the hood of imread 14

Posted by Steve Eddins,

Under the hood of imread  I'm going to play a small trick on you today. Try reading in this JPEG file using imread:url = 'http://blogs.mathworks.com/images/steve/2014/peppers.jpg'; rgb = imread(url); imshow(rgb) So what's the trick? Well, look more closely at this file using imfinfo:info = imfinfo(url) info = ... read more >>

Parameterized software tests and DIPUM examples 5

Posted by Steve Eddins,

Parameterized software tests and DIPUM examples  The book Digital Image Processing Using MATLAB (DIPUM) contains 144 examples. I know this because I watch them all run in MATLAB at least a couple of times a year. I find watching all the images come and go during this process to be oddly entrancing. I have used the MATLAB... read more >>

MATLAB code in an unexpected place 5

Posted by Steve Eddins,

MATLAB code in an unexpected place  The TV show "The Americans" is a show about Soviet Union secret agents pretending to be a normal American couple in 1981-82 or so. In the 2nd season's final episode, which I watched last night, a military officer shows an FBI agent a computer screen that's supposed to be showing... read more >>

Quantization issues when testing image processing code

Posted by Steve Eddins,

Quantization issues when testing image processing code Today I have for you an insider's view of a subtle aspect of testing image processing software (such as the Image Processing Toolbox!).I've written several times in this blog about testing software. Years ago I wrote about the testing framework I put on the File Exchange, and more recently (12-Mar-2013)... read more >>

Color Thresholder App in R2014a 7

Posted by Steve Eddins,

Color Thresholder App in R2014a  I had way too much fun this morning playing with the new Color Thresholder app (new in R2014a) in the Image Processing Toolbox, so I wanted to show it to you. I've shown that picture of M&Ms in this blog before. A few years ago I used that image in a... read more >>

Timing the FFT 3

Posted by Steve Eddins,

Timing the FFT I've seen two questions recently about the speed of the fft function in MATLAB. First, a tech support question was forwarded to development. The user wanted to know how to predict the computation time for an FFT of a given length, N. This user was interested in values of N... read more >>

Comparing the geometries of bwboundaries and poly2mask 5

Posted by Steve Eddins,

Comparing the geometries of bwboundaries and poly2mask  MATLAB user Meshooo asked a question on MATLAB Answers about a problem with the createMask function associated with impoly. Meshooo observed a discrepancy between the output of bwboundaries and the mask created by createMask.I want to describe the issue in more general terms here as a conflict between the geometry... read more >>

These postings are the author's and don't necessarily represent the opinions of MathWorks.