title: Stitch multiple images using OpenCV (Python)
body: <p>Hi have seen a lot of tutorials how to do simple image stitching using two photos and that is no problem.<br />
  But what to do when I want to make a panorama from 4-6 images or more?</p>
  <p>I have code that takes in list of image files(the images are in order from the first image in the sequence to the last). Then for each image I compute the SIFT feature descriptors
  . But then I am stuck, for two images I would set up a matcher using FLANN kd-tree and find matches between the images and calculate the Homography. Similar to this tutorial <a href="http://docs.opencv.org/trunk/doc/py_tutorials/py_feature2d/py_feature_homography/py_feature_homography.html#py-feature-homography" rel="nofollow noreferrer">http://docs.opencv.org/trunk/doc/py_tutorials/py_feature2d/py_feature_homography/py_feature_homography.html#py-feature-homography</a></p>
  <p>But in stead of showing the lines between feature points at the end I have used this <a href="https://stackoverflow.com/a/20355545/622194">https://stackoverflow.com/a/20355545/622194</a> function to make a panorama from 2 images. But I am not sure what to do when I want to add the third and the fourth image to the panorama.</p>
  <p>EDIT:</p>
  <p>From the answers I have tried to implement my image stitching script to calculate a homography matrix between images that are next to each other in the image sequence. So if I have I1 I2 I3 and I4 I now have H_12, H_23 and H_34. Then I start by stitching I1 and I2 using H_12. Then I want to find cumulative homography to stitch I3 to the current panorama. I fing H_13 = H_12*H_23 and stitch the image 3 to the current panorama but here I get very apparent gap in my panorama image and when next image is stitched it is even bigger gap and the images is very stretched.</p>
  <p>Can anyone tell me if I am using right approach for this or can someone spot the error or see what I am doing wrong.</p>