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Pixels in the region of interest (ROI)

asked 2013-08-19 13:58:27 -0500

deiaalencar gravatar image

Hello, could someone help me, I'm new to OpenCV and would like to know how to change a pixel of an roi to another. My program opens an image, divides the image into rectangles with the rectangle function, and would like to know how to change a few pixels from the edges of rectangle. From already, thank you.

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so, you've drawn a grid onto your image. and now ? it's a bit unclear, what you want to do from here on.

could you edit , and be a bit more specific ?

berak gravatar imageberak ( 2013-08-19 15:56:43 -0500 )edit

Then I drew a grid on my image and now I want to change a few pixels that are on the edge of the rectangles, rectangle to another, for example, that the pixel at position (0.159) belongs to ROI1 and I want to put it in ROI2 ...

deiaalencar gravatar imagedeiaalencar ( 2013-08-28 17:02:04 -0500 )edit

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answered 2013-08-19 22:06:02 -0500

To change/access pixel of ROI, it's the same as access/change pixel in the Mat. Indeed, the ROI is just an header for the underling data, therefore:

Mat img = imread( "myimage.jpg" );
Rect my_roi( x, y, w, h );
Mat ROI = img( my_roi );
Vec3b pixel = ROI.at< Vec3b >( pixel_x, pixel_y );
// Swap color for the first pixel (BGR => RGB).
char tmp = pixel[0];
pixel[0] = pixel[2]; // set blue to red value
pixel[1] = pixel[1]; // do nothing on green
pixel[2] = tmp; // set red to blue

I use vector (Vec3b) in that sample, but you could use char or Ptr aceess on anything you want. Look at this page for the performance evaluation of accessors.

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But in this case I'll be changing the value of the pixel and not the position, in fact I need to get the pixel is on the edge of ROI1 and put it in ROI2, so that by the time I go to print the image on the screen no longer appears she divided into rectangles, but a little deformed.

deiaalencar gravatar imagedeiaalencar ( 2013-09-02 08:15:23 -0500 )edit
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Asked: 2013-08-19 13:58:27 -0500

Seen: 3,087 times

Last updated: Aug 28 '13