Comments on: Timing code in MATLAB

By: Amin

Amin — Tue, 24 Aug 2010 20:09:16 +0000

Hi Steve,

I m a little bit late to ask this on your Blog.
So, im using an ActiveX Control of a DAQ Board.
I need to generate a code in a loop which have to be determined to work in 50 ms, the problem is that this loop have many Methods and Properties.

Can you tell me which timing I must use for it ?

Thanks

By: Steve

Steve — Thu, 29 Oct 2009 17:47:00 +0000

Muhammad—timeit doesn’t have anything to do with parallel processing. Many MATLAB functions are already multithreaded and so will automatically use multiple processor cores. If you are interested in explicit parallel programming, you might be interested in the Parallel Computing Toolbox.

By: Muhammad jahanzeb

Muhammad jahanzeb — Thu, 29 Oct 2009 05:57:44 +0000

i want to know that how i can use ‘timeit’ for parallel processing.In linux we do ‘fork’ which makes parent and child and processor fastly switch between parent and child to service them.How can we do this thing in matlab.i have to make two functions and processor should switch between these two functions so that it seem that we are doing parallel processing of two functions.

By: feelfree

feelfree — Wed, 05 Mar 2008 22:53:54 +0000

Thanks Steve, i see.

By: Steve

Steve — Wed, 05 Mar 2008 16:30:42 +0000

Feelfree—There’s no real problem here. You’re just seeing the affects of interpolation. Try this:

imshow(I - III, [])
impixelinfo

and then move the mouse over the image. You’ll see that the difference is zero just about everywhere except for along edges, which is what you should expect because of the interpolation approximation.

If whatever you are doing is sensitive to this, then you’ll need to rethink your approach.

By: feelfree

feelfree — Wed, 05 Mar 2008 16:12:46 +0000

Thanks Steve, and I do as you suggest, and in this case the output image is of the same size with the original one, but their gray value still have difference though not much. The average gray value difference is about 2 gray level for uint8 type image. sum(abs(III(:)-I(:)))/256/256*256. Then how can I deal with this problem? Thanks. Hope I did not throw a spanner in your current topic.

By: Steve

Steve — Wed, 05 Mar 2008 14:40:49 +0000

Feelfree—Use the ‘Size’ parameter in your second call to imtransform.

By: feelfree

feelfree — Tue, 04 Mar 2008 21:32:19 +0000

Hi Steve, I write to have a disscussion with you on MATLAB function imtransform.

My question is how to get back to the original image after some kind of transformation, for example affine transform. The following codes can illustrate my question:

I = imread(‘cameraman.tif’);
I = im2double(I);
delta = pi/6;
t = [ 2*cos(delta), sin(delta), 0
-sin(delta), 2*cos(delta), 0
3, 4, 1];
tform = maketform(‘projective’,t);

[II,xdata,ydata] = imtransform(I,tform);
figure;imshow(II,[]);

%%
revt = inv(t);
revtform = maketform(‘projective’,revt);
III = imtransform(II,revtform,’UData’,xdata,’VData’,ydata,’XData’,[1,256],’YData’,[1,256]);
figure;imshow(III,[]);

Hower, the orignal image I and III are different not only in theirwidth and height but also in their gray value.

Would you like to open a new topic on this problem?