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 >>

roifill design critique 6

Posted by Steve Eddins,

roifill design critique  "Is there anything else you would like to tell us?"This was the question whose answer led me to revisit an old friend of mine, the roifill function. This is a function that smoothly fills a specified region of interest in a gray-scale image. I implemented it in the early 1990s... read more >>

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