Hugin tutorial — Stitching two photos together
The entire process described here, of taking two handheld
photographs and sticking them together into a single image, can be performed
completely automatically by just clicking Align in the hugin Assistant tab. This tutorial looks 'under the hood' of Hugin and
introduces some of the concepts and functions that are needed for more advanced
use.
Note: This tutorial is based on the 0.7.0 version of Hugin. Although
your version may differ, the underlying principle will remain the
same.
You can download the two photos used in this example (974-1.jpg, 975-1.jpg) and try it
yourself.
Start by launching Hugin, and using the Images tab select Add individual images... button to
select the two images you want to stitch.
Tip: you can select multiple
images in the file dialog box or drag and drop files from a suitable file
browser.
Select image #0 then click on Anchor this
image for position and Anchor this
image for exposure. You might want to try this tutorial again later
selecting image #1 to see what difference these choices make.
If you select or drag in image files which don't have complete EXIF data,
the Camera and Lens data dialog box will open asking for camera
and lens data. For a normal pocket camera it is usually safe to enter 50 deg for the HFOV (Horizontal Field of View).
Switch to the Control points tab, this is where
you are going to input all the information the software needs to align the two
images.
Click on the title bar above each image to select image 0 on the left hand side and image 1 on the right hand side.
Make sure that Zoom is set to fit
to window and that both Auto fine
tune and Auto add are set.
Now you can use the mouse to select control points; pick well defined
features that you can see in both the left and right-hand window.
Hugin aligns images using these control points, each is actually a
pair of locations, one for each of the two images being connected.
When you first select a point a high magnification window will open to help
you with selection. If you hold down your left mouse button you can roam around
until you have the cross hairs just where you want them.
For the first control point you will then need to go to the other
image and click the corresponding location, Hugin will then automatically
fine-tune this position. For subsequent points, when you have finalised your
selection on the first image Hugin will automatically find the point in the
second image.
Repeat until you have about 5 or 6 pairs of control points.
Now select the Optimizer tab. Hugin uses an
optimisation scheme where it adjusts image orientation and lens settings of
source photos until the control-points line-up.
The plan here is to keep the first image fixed and adjust the position of
the second image to fit. You can do this by selecting Optimize
Positions (incremental, starting from anchor).
However the lens parameters can be optimised at the same time; for now
optimise HFOV (horizontal field of view) and correct barrel distortion
by selecting Optimize Positions, View and Barrel
(y,p,r,v,b).
Tip: Although you can optimise
all hfov, a, b, c, d & e parameters, most of the time the hfov and b
parameters are the only significant lens numbers you need to consider.
Click on the Optimize now! button and wait while
the optimiser tries to find a good fit. When it is done you will need to Apply the changes.
Select the Exposure tab. Choose Low dynamic range and click Optimize now! You might want to try this
again with a different optimisation setting to see the effect.
Before we generate the stiched panorama, select Preview panorama icon (or find it in the View menu).
In this window we need to set the projection to Rectilinear, this is equivalent to a normal wide angle
camera.
The Straighten icon can be used to
automatically centre, level and fit the field of view to the images. You can
alternatively do this manually by adjusting the sliders at the edges and by
clicking in the preview itself to re-centre the view.
Finally we are going to generate the output image. Select the Stitcher tab.
The projection should be Rectilinear, and having adjusted the field of view
in the preview window these settings should not need to be altered. Select Blended panorama under Normal output, and under File formats - Normal output choose whatever
suits you. Here we have chosen JPEG.
Select Save project and stitch.
Firstly, project files will be saved to your selected location (these can be
opened again later in Hugin to revisit the process) and finally you will be
asked for a filename prefix for the final panorama. |
