imagesc after fft2

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Michal Karwacki
Michal Karwacki 2017-12-15
评论： Image Analyst 2017-12-16
Hello - im new in here :)
I've got some kind of radar's signal that I want to show with the imagesc() function.
After an fft2 I wanted to show my signal with:
figure; imagesc(abs(tabsygn-mean(y,2)));
It all worked, however when I went to reduce my axis size, something strange happened. It changed the values, however the image itself didn't change. I've used the command below:
imagesc(0:200,250:400,(abs(tabsygn-mean(y,2))));
The image on the left is original, and on the right is after the command above.
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Michal Karwacki
Michal Karwacki 2017-12-15
No, black dot appearded when I exported the figure into jpg. I wonder how to cut out the yellow line and create image with y(150:450) and x(0:900) from the original image
Adam
Adam 2017-12-15
The arguments you pass as x and y to imagesc to not change the image at all, they just give the values for the x and y data to put on the axes.
If you want to clip an image you do this in the normal way, after plotting it, using
doc xlim
doc ylim
or
doc axis

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Image Analyst
Image Analyst 2017-12-15
Try
yourImage = abs(tabsygn-mean(y,2));
% Extract only rows 150-450 and columns 1-900.
yourImage = yourImage(150:450, 1:900);
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Michal Karwacki
Michal Karwacki 2017-12-15
well i feel stupid now. It all worked - thanks a lot
Image Analyst
Image Analyst 2017-12-16
Well, it's a common beginner mistake so you just joined thousands of other who do the same thing all the time.
Beginners think matrices are indexed m(x,y), but they are NOT.
They are indexed m(y, x) because rows are y and columns are x, and it's the rows that come first in the index list.

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