How does macthTemplate() deal with scaling?

matchTemplate

asked 2017-07-27 03:08:46 -0600

CVLearner17
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 matchTemplate(Image, Template, ResImage, CV_TM_SQDIFF);

If size of "Image" changes, matchTemplate() can't find location of "Template" in the "Image".

Should "Template" be exact part of "Image" in order for matchTemplate() to find its location?

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answered 2017-07-27 06:50:54 -0600

Raki

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Take a look at this, it explains how one could make Template Matching scale invariant.

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Thank you very much!

CVLearner17 ( 2017-07-27 11:09:16 -0600 )edit

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answered 2017-07-27 03:29:54 -0600

StevenPuttemans

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updated 2017-07-27 03:30:58 -0600

In principle matchTemplate does not incorporate scale invariance. But you can introduce it yourself.

Start from your original image
Apply a couple of pyrUp and a couple of pyrDown, creating a scale pyramid
Now run matchTemplate with a fixed template on all images, be sure to use TM_SQDIFF_NORM <-- the normalized is important here
Now for each scale take best match, store it in vector.
Then over all best matches in vector take strongest one (so with the smallest difference).

Also about being an exact part of original image: NO it does not. The sample is made that way and confuses people, but in general, in an application the template is NOT related to the image where you apply it.

Good luck!