Autostitch

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

📃 These are primarily notes, intended to be a collection of useful fragments, that will probably never be complete in any sense.

Autostitch is a free-for-personal-use photograph stitcher (see e.g. examples on flickr) that can basically work with any pictures, and without assistance. In practice, you may want to tweak the options if your pictures aren't the best stich material.

Download here.

To think of while taking photos

• It seems that the more overlap, the more likely autostitch is to fit together things. Go crazy with half-overlapping images if you have a digital camera, it will only cost you a little space...

• Difference in focus won't necessarily confuse autostitch, but will often look weird. If sensible, e.g. if it's (near-)infinity focus anyway, focus once and change to manual focus. You may also want to avoid shallow depth of field by setting a tighter aperture.

• Similarly, indoor pans past windows may be exposed differently. (D)SLRs will often allow you to lock the exposure settings (e.g. on Canon: * with the shutter half-pressed)

• Extreme (and also cheaper) zoom lenses may show (barrel) distortion at the widest zoom part, which may confuse autostitch. Zoom in a little. Again, if you have a digital camera, experiment, e.g. taking two pans at different zooms. You can also use a program to lessen this distortion, but you probably lose some border that way, so that's probably only worth it indoors and when shooting with largee overlap.

• A tripod is not necessary at all, but will help sharpness, and also help the images line up better. I've made several wide panoramas that bend off on one end - although using some vertical reference will also work.

• I have heard it said that you should rotate the camera around the focal point, usually a little in front of the lens. While this may be some semi-intuitive nonsense or nor, it probably isn't a bad idea to pivot roughly around the camera and not your shoulders if there are close objects in the shot.

Pre-editing

While autostitch does detect rotation, it doesn't do so very well; it seems to work better with horizontal stitches, and possibly works better with the images pre-rotated (you can use the windows viewer to do this).

Getting a strangely bent stitch with quite curved black bits result is a good sign of this causing problems, so rotate the images so that they line up to stitch horizontally.

I suppose the rotation option does the same thing. I haven't tried this.

You can lessen barrel distortions and such with things like PTLens or DxO.

Settings to tweak

You can quickly test options at 10% size. Once you're happy, do it at 100% (or less if 100% is an insanely high resolution and takes forever).

However, the difference in resolution does matter to the further steps, so don't set it ridiculously low. Also, changing no options except the size seems to mean no recalculation of some things, which is generally fine but mayy not be with such large size differences, I'm not sure.

Gain Compensation: Enable (usually). This blends pictures into each other brightness-wise. Since digital cameras and (D)SLRs have automatic lighting you will likely make pictures with different brightness. You may well want to enable this compensation, unless you intentionally used a manual lighting on your camera (to e.g. get the sun and moon on one panorama and therefore want one side to be really dark and the other really light).

The Matching Options basically control how strict matches have to be:

• When nonsense overlaps happen, make alpha and/or beta higher. (but know that this can also be caused by impossible-to-stitch images, particularly with very close objects)
• When no match is found, lessen the strictness: make alpha and/or beta lower
• Setting the max iterations a lot higher can make almost-matches work a little better. You can easily make this 10000 since the RANSAC step is usually quite short relative to the blending step anyway (only long when images are many-megapixel), though setting it that high may be somewhat futile.

When it is hard to find good stitches, you'll have to use trial and error here.

After you change settings, you should re-run with 'Stitch' → 'Start'. It only does that automatically the first time.