which image will be above the other image in stitching process??

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Relative images position is decided knowing homography. Of course Homography needs matching features to work

Thank you LBerger, if you know any useful link to explain the concept please provide me with them if possible.

You have got some reference in this post

Hello LBerger, thanks for the reference, but from what i understand the homography is a transformation matrix that helps in warp one image into other (is that true ??). what i want to know is how to decide which image is warp into another? for example, if i have two images to stitch and after extract and mach the features and compute the homography should i warp the second image into the first one or should i do the opposite??

I'm not sure to understand your problem. Homography doc is here. Of course dstpoint= H srcpoint or srcpoint =H^(-1) dst. But result image size result would be the same. You have to warp image corners to find this size and after warp each image in this new image. After problem is how to blend seam point and correct exposure.

What i mean is if i warp the second image into the first image the (overlap area) in the resulted image will be taking from the second image and vise versa. I am using Opencv stitching class and i want to know how it decide which image warping into other.

This work is not done in homography but in exposureCompensator and seamFinder and Blender. You should used this sample to understand each step

Thank you very much. I tried to run the example but there are some missing files, also i tried to understand how the seamFinder choose the seam line but i didn't find any explanation of this procedure !! if you know any useful resource please help me.

What do you mean by there are some missing files? If you 've got problem with this sample you can use this one (same without a bug )

they can't find this files:

#include <opencv2/core/utility.hpp>
#include "opencv2/imgcodecs.hpp"
#include "opencv2/stitching/detail/timelapsers.hpp"