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How to choose a specific area of an image?

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Ann G
Ann G 2015-10-5
评论： Image Analyst 2017-12-9
I would like to ask you how to choose a specific area of an image and then use the elements of this content?
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Yap Sam
Yap Sam 2017-12-9
Hi, I have a question here. Lets say, I have defined an area of polygon using its x and y coordinates. But,how do I able to find out the mean pixels intensity of this area of polygon? Secondly,how should I apply the"if" condition to thershold a certain value of mean intensity of this polygon area.
Kindly advice
Image Analyst
Image Analyst 2017-12-9
Make a mask and then use mean on the masked image:
mask = poly2mask(x, y, rows, columns);
theMeanIntensity = mean(grayImage(mask));

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Stephen23
Stephen23 2015-10-5
You need to use some kind of array indexing. Often the easiest is to use logical indexing, which would allow you to select the area that you want.
http://www.mathworks.com/help/matlab/examples/manipulating-multidimensional-arrays.html

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Image Analyst
Image Analyst 2015-10-5
If you want masking demos, ask me.

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