OpenCV,Warp images by Homography matrix

Question

I followed Panorama – Image Stitching in OpenCV to do same task on Android,by using openCV4Android.My problem is in about warping image by founded homography matrix.I tested these images:

image1:

enter image description here

image2:

enter image description here

Result of warping image1 by founded homography is:

enter image description here

You can see that result is good warped but first part of that(left side) is cut! So stitching result was:

enter image description here

And result of above images in referenced link page,is:

enter image description here

Why warping by homography cut that?Or may be I did some things wrong?

Zaphod · Answer 1 · 2015-01-20T08:27:59.200

1

Image 1 does not have any information about the rest of the scene. Since you're only applying the homography on image 1, it gets warped with respect to image 2 but doesn't really add any further scene information.

To get the resultant image you need, check the furthest x and y shift of image 1 after warping, and add this missing region along with stitching image 2. This isn't as simple as an addition, because the resultant image is larger, but it isn't too complicated either.

edited Jan 20 '15 at 08:27

answered Jan 20 '15 at 05:09

Zaphod

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I tried to follow what I linked at first and tested it's images.But why it's result is OK? – hasanghaforian Jan 20 '15 at 14:50
Not sure why you edited out your code... Anyway, if you compare your code and what you've linked, the part where the result image is initialised, and where warped image 1 and image 2 are copied to it, are completely different. Comparing these portions line by line will answer your question. – Zaphod Jan 21 '15 at 04:51

score 0 · Accepted Answer · edited May 23 '17 at 12:05

OK! Finally I could solve the problem.I saw this answer and understand what causes this problem and how I can solve that:

The problem occurs because the homography maps part of the image to negative x,y values which are outside the image area so cannot be plotted. what we wish to do is to offset the warped output by some number of pixels to 'shunt' the entire warped image into positive coordinates(and hence inside the image area)...So just premultiply your homography by a matrix similar to the above, and your output image will be offset.

OpenCV,Warp images by Homography matrix

2 Answers2