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Local Contrast by dragging rectangle on an image

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Muhammad Abir
Muhammad Abir on 22 Dec 2020
Answered: Hrishikesh Borate on 31 Dec 2020
Hello,
I am trying to develop a code that can allow user to draw a rectangle or arbitrary size. Then when the user drags the rectangle, it will enhance the contrast of the region inside the rectangular area only. I tried to use drawrectangle and addlistener but it looks like it not working as I want. In my code, when I display the image, the contrast enhanced aera is cropped and displayed in the upper corner of the image, but my plan is that the the contrast enhanced image will be displayed on top of the origianal image at the location the rectangle is selected. Here is my code so far:
imshow('cameraman.tif');
roi = drawrectangle('LineWidth',2,'Color','red');
addlistener(roi,'MovingROI',@(r1,evt) allevents(Img, r1,evt));
function allevents(Img, src,evt)
evname = evt.EventName;
roi= round(evt.CurrentPosition);
switch(evname)
case{'MovingROI'}
CroppedImage= imcrop(Img,roi);
end

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Answers (1)

Hrishikesh Borate
Hrishikesh Borate on 31 Dec 2020
Hi,
I understand that you want to define a dynamic rectangular region of interest and enhance the contrast of the region inside the rectangular area only.
For contrast enhancement, several techniques can be used, as shown here. In the following code, imadjust is used.
I = imread('cameraman.tif');
himg = imshow(I);
roi = drawrectangle('LineWidth',2,'Color','red');
addlistener(roi,'MovingROI',@(src,evt)allevents(I, himg, src, evt));
function allevents(Img, himg, src,evt)
evname = evt.EventName;
switch(evname)
case{'MovingROI'}
rectPos = evt.CurrentPosition();
croppedImage = imcrop(Img, rectPos);
enhancedImage = imadjust(croppedImage);
newImg = Img;
newImg(rectPos(2)+(0:rectPos(4)), rectPos(1)+(0:rectPos(3))) = enhancedImage;
himg.CData = newImg;
end
end
For more information, refer to drawrectangle.

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