Finding coordinates of a rectangle in a picture

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Alice
Alice on 3 Oct 2016
Answered: Mihaela Duta on 11 Oct 2016
I'm running an eyetracking experiment. I display an image using the Screen function from psychtoolbox and I want to know the coordinates of some of the items displayed in the picture. Is there a way of drawing a rectangle on the positions you want to find the location of? Or is there another way of doing it? Thanks.

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Answers (3)

KSSV
KSSV on 3 Oct 2016
You can draw rectangle using imrect.
doc imrect.
You can interactively pick the coordinates from the plot/ figure using ginput().
doc ginput.
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Alice
Alice on 4 Oct 2016
What do the x and y coordinates that you get from ginput relate to? Are they pixels, or are they just coordinates on an arbitrary scale?
KSSV
KSSV on 4 Oct 2016
They are the coordinates/ locations where you have clicked.

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Ann G
Ann G on 3 Oct 2016
You can use the ginput and save the coordinates x,y by choosing the items.
[x,y]=ginput;
save x
save y
Mihaela Duta
Mihaela Duta on 11 Oct 2016
Edited: Mihaela Duta on 11 Oct 2016
I would suggest to use an image processing package to identify the areas of interest in your picture. You can use Adobe Photoshop if you have it, but gimp is an excellent free alternative (https://www.gimp.org/).
I am not sure whether you want to use these regions of interest when displaying the picture during the experiment, or for data processing. If you want to highlight regions of interest during the stimuli presentation, you can do that using the FrameRect function from Psychtoolbox.

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