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filter2D and sepFilter2D, specifying the value for a constant border

asked 2012-07-12 17:25:06 -0500

LoopUniverse gravatar image

updated 2012-07-13 20:42:46 -0500

When calling filter2D and sepFilter2D, I want to use a constant border, which I do by providing BORDER_CONSTANT for the "borderType" parameter as specified in the documentation (http://docs.opencv.org/modules/imgproc/doc/filtering.html?highlight=gaussianblur#filter2d).

However, I do not see how I can specify WHAT I want that constant value to be. How do I achieve this?

(edit: I did find that the default constant border value seems to be 0.)

(edit in reply to Alexander, I do not see how to reply directly to answers: If I am not mistaken, copyMakeBorder will allocate a new image and copy the input image to a subregion of that new image. That seems a little excessive just to get access to the the ability to have non-zero constant border interpolation methods. Is there any other way to change the constant border value that does not require such memory allocations and copies?)

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Please use links to docs.opencv.org, because opencv.itseez.com may be shut down at some point...

Kirill Kornyakov gravatar imageKirill Kornyakov ( 2012-07-13 01:59:28 -0500 )edit

The source for filter2D does a copyMakeBorder anyway, perhaps this is cheaper than doing a range check on every iteration as that would introduce branches? (i.e. If inside use the pixel value else use a constant value) https://github.com/Itseez/opencv/blob/5f590ebed084a5002c9013e11c519dcb139d47e9/modules/ts/src/ts_func.cpp#L787

_Robert gravatar image_Robert ( 2014-09-18 15:40:39 -0500 )edit

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answered 2012-07-12 17:37:47 -0500

AlexanderShishkov gravatar image

updated 2012-10-02 06:09:09 -0500

V.G. gravatar image

If you want to use BORDER_CONSTANT, you should manually add border to your image with copyMakeBorder) function (see tutorial)

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Asked: 2012-07-12 17:25:06 -0500

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Last updated: Oct 02 '12