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Image stitching - why does the pipeline include 2 times resizing?

asked 2014-04-22 04:43:18 -0500

rbaleksandar gravatar image

updated 2014-04-22 04:57:38 -0500

Hi all!

I have been working on a project involving image stitching of aerial photography. The stitching pipeline that is given in the documentation of OpenCV I actually encountered many different books and papers and frankly it makes perfect sense (http://docs.opencv.org/modules/stitching/doc/introduction.html). Except for one thing. In the two stages presented there (image acquisition being the first out of three but no point including it there) - registration and composition - I encounter resizing first to a medium and then to low resolution. Can someone explain to me why that is? Does the resizing in the registration stage has to do anything with the feature extraction? The only thing that makes sense to me in all this is that we obviously need the same resolution for all images in an image stitching. Another reason for the additional resizing this time in the composition stage is the computation of masks, which are then applied on the high resolution images that we give as input at the very beginning.

Thanks a lot for your help!

PS: Also with resolution it is obviously meant the number of pixels (since resizing is used in the stitching example), which is somewhat controversial since resolution per definition also depends on the size of each pixel and not only on their numbers as it defines the amount of detail in an image.

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answered 2014-10-22 06:33:00 -0500

Duffycola gravatar image

As far as I know there are different scales used in different stages of the pipeline.

Initially there is something called work_scale, which resizes the images to a more convenient size (trade-off between quality/processing time).

Then there is something called seam_scale, which is used right after feature detection/description. During "seam finding" the stitching pipeline finds the best seams where to cut off two overlapping images. In other words, it looks better to cut off where neighbouring pixels are similar instead of assuming that the pixels along the image boundary will look like the other picture.

Finally there is something called compose_scale, which, I think, is used to control the final stitched image size.

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Asked: 2014-04-22 04:43:18 -0500

Seen: 623 times

Last updated: Oct 22 '14