How i can use the below code to find the exact overlap.

[kuldeep203]

For reference i am sending you the 2 images with 20 pixel overlap. So i can find exact displacement for exact overlap.

#!/usr/bin/python
  
import sys
import pyvips

# you can set the size of the window as well, but 10x10 pixels (the default) is
# probably fine

left = pyvips.Image.new_from_file(sys.argv[1])
right = pyvips.Image.new_from_file(sys.argv[2])

# the expected overlap, or the number of pixels the two images have in common
overlap = int(sys.argv[3])

# harea is the maximum displacement we detect, in pixels ... this is half
# the size of the area searched

# bandno is the band we search in ... green (band 1) is best for JPG images,
# since it has double the resolution

# dx0/dy0 are optional output args ... we set them True and pyvips will return
# their rvalues in result

join, optional = left.mosaic(right, 'horizontal',
                             left.width - overlap, 0, 0, 0,
                             harea=15, bandno=0,
                             dx0=True, dy0=True)

print 'horizontal offset =', optional['dx0']
print 'vertical offset =', optional['dy0']

print 'writing join to x.png ...'
join.write_to_file('x.png')

This is doing a 0th order (ie. just translation) join of two images left-right. It has a relatively robust thing for finding the overlap:

1. Split the overlap area into three sections, top middle and bottom.

2. Search the reference (left) edge for tie-points (high contrast areas) and collect the top 20 in each zone.

3. For each tie-point, search the corresponding area on the right, assuming the start overlap.

4. Put all the best match displacements into a model, find the best translation, and discard the worst pair of tie-points.

5. Repeat 4. until either we have a translation which fits all tie-points well, or we don't have enough tie-points left.

6. Do a feathered join, return the found best displacement.

With this pair of test images:

I see:

john@yingna ~/try $ ./find_overlap.py cd1.1.jpg cd1.2.jpg 100
horizontal offset = -426
vertical offset = 0
writing join to x.png ...

You don't need the joined images, so remove the write_to_file and it won't be generated.

In your LMS optimisation, you'll need to have something to handle missing displacements where the edges just didn't have enough information.

Originally posted by @jcupitt in https://github.com/libvips/pyvips/issues/40#issuecomment-386576906