Image Stabilization for Bicycle Video
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This article is one of a series on shooting video from a bicycle. Much of this article is applicable to other video shoots.
Roads and paths can be bumpy, and off-road riding is even bumpier (though some potholed streets and root-heaved paths compete rather well...). Your head nods with each bump, especially if you ride in a racing position that hangs your head low.
Bumps cause three common problems with video:
As you ride, your senses of balance and body position direct your eyes to steady your direction of view. But your eyes do not have this assistance when you are looking at an image on a screen. An unstabilized image is hard to watch.
Shake during exposure of the image blurs the picture. This can be avoided by steadying the camera, by using short exposure times, or by one kind of in-camera image stabilization.
Another common problem resulting from shake is geometric distortion due to two effects:
There are several ways to reduce these problems. Classic solutions are to mount the camera on a tripod, or to have the camera rig roll on smooth tracks. These are not available when riding a bicycle.
Rising off the saddle when riding over bumps can spare your body, and steady a video too, with a helmet-mounted camera.
The heavier the camera, the looser its attachment and the higher it sits off the helmet, the more it will tend to shake..
Surprisingly, mounting the camera directly to the bicycle can result in very little apparent shake, if the camera has a wide-angle lens and the riding surface is smooth. The length of the bicycle's wheelbase and the rigidity of its frame avoid the nodding motion of a head-mounted camera. The camera must be rigidly mounted, though. A loose or flexible mount will amplify vibration.
Any camera mounted to the bicycle will lean with it in corners, and other bicycle motions also affect the image. These depend on how and where the camera is mounted.
A forward-facing camera on the helmet turns with your head to look in the direction you are looking, but a rearward-facing camera mounted on the helmet turns to point in some odd direction that doesn't make any sense. To get good use out of a helmet-mounted rearward-facing camera, you must become skilled in the use of a rear-view mirror, and remember not to turn your head, so you don't spoil the shot.
A rearward-facing camera mounted on the rear rack or seatpost of the bicycle always looks directly rearward. This camera has a low-perspective view, but that is usually not a problem unless you are riding in tight formation with another cyclist. Even then, the cyclist behind you could ride slightly off to one side so that the camera can see past. You might also possibly construct a scaffold to raise the rearward-facing camera closer to eye level.
A forward-facing camera mounted on the handlebar can have less shake than a head-mounted one, but it turns with the handlebar, so the image has a slight weaving motion as you balance the bicycle. The handlebar never turns very sharply, and so the camera will not look in the direction you turn your head – a real disadvantage. A camera could also be mounted to the frame of the bicycle or to a front rack, and then it won't weave.
In either case, the camera will lean with the bicycle, which is realistic when cornering but annoying when stopped. You must remember then to keep the bicycle upright.
Most helmet cameras have an extreme wide-angle lens, which takes in most of what you see with your eyes, and reduces the apparent amount of shake. By making things look farther away, a wide-angle lens makes you appear to be going faster. For example, if a car is 50 feet away and a wide-angle lens makes it look 100 feet away, then it will appear to be approaching at twice its actual speed. This can be misleading and disturbing.
Generally, the increased apparent speed is more disturbing with a forward-facing camera, and so a somewhat narrower field of view is desirable – but this increases apparent shake. There are some tricks you can use to reduce the shake --
Soft tires and suspension may slow you a bit but again, on-bike video will usually make it look as though you are going faster than you really are. Suspension reduces discomfort and the likelihood of damage from hard hits, but soft tires actually do more to reduce vibration.
Videographers often use “steadicam” accessories. One common kind uses a pivot so a hand-held camera can swivel and keep pointing in the same direction, even as the videographers' walking motions disturb the handholds. I don't know of any such device for use with a helmet-mounted camera. That is unfortunate, because physically steadying the camera avoids blur as well as shake. I might try to make a steadicam device using the pivots from an old phonograph tonearm. The device would need springs and a damper to keep the camera steadily pointed in the right direction.
If you can't keep the camera steady, then there is image stabilization, either in the camera or in post-processing.
Optical image stabilization moves a part inside the lens, or moves the camera's sensor. Digital image stabilization uses a motion sensor in the camera to reposition the image rectangle, and can be done either in the camera or in post-production.
Many small digital still cameras and camcorders have optical image stabilization. More and more action cameras have digital image stabilization, so it is now (2020) universal in high-end models.. They have different advantages and disadvantages..
Optical image stabilization, like a steadicam accessory, can hold the image steady during exposure, and so can work extremely well for long exposures of still images with a handheld camera. In my experience, optical image stabilization is less successful for rapid vibration and when the camera is panning. Optical image stabilization cannot look ahead in time, and so it may interpret intentional panning as shake – then jerk the panned image when the stabilization reaches the limit of its travel.
Digital image stabilization responds to a motion sensor in the camera, or compares stored images. Digital image stabilization can't hold the image steady during exposure, and so only high shutter speed can prevent blur. For this reason, digital image stabilization works better in bright light. Digital image stabilization can look ahead in time, and so, can discriminate between shake and panning. This can in theory be done in the camera, but it is processor- memory-intensive, so it is typically done in post-production, taking advantage of the far greater capabilities of a high-end desktop or laptop computer. Digital image stabilization can compensate for changes in image geometry as it moves around the sensor.
An analog video image is generated by a single dot that scans across the camera's sensor and the display screen, in the same way you are reading this page: from left to right, on one line after the other from top to bottom. The analog signal takes lots of bandwidth, because the dot must be able to change from light to dark and back hundreds of times on each line, and there are hundreds of lines in the image, which is typically scanned 25 or 30 times per second.
An image must flicker 50 or more times per second so you don't notice the flicker. In order to hold down signal bandwidth, analog TV uses interlaced scanning – odd-numbered lines in one scan,which lasts 1/50 or 1/60 second; even-numbered lines in the next scan. The same is the case with many digital cameras, and broadcast television, at 1080-line resolution. At a normal viewing distance, you don't notice the individual lines flickering, but the bandwidth is halved. Interlacing also makes motion look smoother, because the scan rate is twice the frame rate. On the other hand, objects which move upward or downward in the image can look jagged when their speed is a close match for the progression of interlaced scan lines.
Interlaced scanning poses a problem for image stabilization. Because the even-numbered and odd-numbered lines are scanned at different times, image stabilization will produce a double image when the camera shakes. Or, if the image stabilization works independently on each scan, the images will look jagged because they are composed only of every alternate line.
Image stabilization works much better following de-interlacing. Se our article about it for details.
Digital video is commonly scanned progressively -- all in one sweep. Progressive scanning is much preferable when image stabilization will be used. Flicker is no problem with digital storage because an image can be read out multiple times to a display that runs at a higher scanning rate. Modern displays don't flicker anyway: each dot of the picture stays lit up until it is refreshed with new data.
Interlaced scans can be converted to progressive scans in software. The best deinterlacers sense which parts of the image are moving, preserving full resolution whenever possible. A good deinterlacer is available in the free Windows application VirtualDub. It even allows doubling the scan rate, which can be useful as preparation for software image stabilization. See our article about deinterlacing for more detail..
As already mentioned, image geometry changes with camera aim. As an example, if the camera aims upward, a building appears smaller at the top.
A wide-angle lens reduces the apparent size of objects in the image and with it, the apparent shake, but on the other hand, objects appear larger near the edges of the image. Digital image stabilization moves the displayed image around in the recorded image, causing noticeable changes in shape of objects in a stabilized image shot with a wide-angle lens.
Extreme wide-angle fisheye lenses, used in most action cameras, create an additional distortion. A fisheye lens compresses the image nearer the edges – but then, straight lines at the edges curve like parentheses. You see that with trees, lampposts and buildings.
A fisheye-lens image would look normal when projected with another fisheye lens onto on a concave, hemispherical viewscreen. That is how IMAX movies work – but most of us still only have a flat screen at home.
Because of the compression of the fisheye image near the edges, objects maintain nearly the same width as they pan toward the edge. A fisheye image is actually less distracting than a rectilinear lens in a wide-angle panned shot, or a shot from a bicycle in motion. But the fisheye lens leads to a problem with image stabilization, most obvious with lines that extend from side to side in the image. A straight line – for example, the horizon -- which passes through the center of a fisheye-lens image will appear straight. If camera shake makes the line pass above the center, it will appear to bend downward at the edges, and if below the center, upward. If stabilization corrections are large, objects noticeably change size and shape as they move.
The following two video examples illustrate this. The differences are easiest to see in a full-screen view. A full-screen icon will appear at the lower right when you mouse over the moving video. Click again at the lower right or strike the ESC key to return to this page.
The first video is unstabilized.
Unstabilized video
The second example has been stabilized using the Windows application Deshaker (about which more later...). I've restricted the area of the image which Deshaker senses, for the best stabilization at the center but with noticeable errors at the edges. You may also notice discontinuities in the image at the edges: I configured Deshaker to use previous and following frames to fill in areas not included in the current frame. Zooming in slightly moves those areas off the screen, as described in the next section of this article.
Stabilized video
Because image stabilization software must shift the image, either it must be enlarged, or blank areas will appear at the edges. Better image stabilization software lets you choose how you manage this. There are several options.
Leaving blank borders in the picture provides a great demonstration of how image stabilization works, and is good for video that has to be used as evidence in a courtroom – you can't be accused of leaving anything out. It's rather distracting, though.
You may simply choose a zoom level. This works fine as long as the shake isn't too extreme. If your video editing software supports keyframing (to adjust zoom during a clip), you can enlarge the image only as needed during the shakier parts of a clip.
Another common option is for the software to adjust the zoom level so the image fills the screen. This may be for an entire clip, or it may adjust itself during a clip. But then you may get the Alfred Hitchcock zoom effect…
In the mid-1950s, legendary film director Alfred Hitchcock made creative use an early zoom lens in his film Vertigo. He zoomed the lens in while moving the camera away (and vice versa) to create a weirdly shifting perspective. I won't spoil the experience for you by describing the scene. See the movie. It's a classic.
Image-stabilization software with auto-zoom can give you the same effect, and it can even look as though you are riding your bicycle backwards for a moment, then forward again. This is distracting!
You avoid this by setting the stabilization software to a constant zoom level, or setting the auto-zoom to work slowly.
Enlarging the image to remove the black borders will unavoidably result in a loss of sharpness. This is hardly noticeable though with the typical small amount of enlargement needed. You could shoot at high resolution, then afterwards reduce resolution as needed.
At least one image stabilization application, Deshaker, offers a very neat feature, filling in the borders with data from earlier or later images. This is often undetectable with the minor amount of enlargement necessary for a good result in a bicycle video..
Manual zooming with auto fill-in removes blank borders with the least obvious side-effects.
Now we get down to specifics. I have two cameras with image stabilization .I've used two image-stabilization applications which run under Windows which benefit, as you might expect, from a very fast processor. YouTube also now is offering image stabilization -- and does the processing on its own server. A 360-degree camera can stabilize the image without creating borders, and we review one.
My two cameras with image stabilization are a Git2 Pro and a Sony HDR AS100V. There is a review of the Sony on this site, giving a lot of attention to its image-stabilization feature. The Git2 Pro's image stabilization works similarly.
Deshaker is available as a free download. You run it as a filter in VirtualDub, which also is free. Please donate to the developers: I did. Plugins are available so VirtualDub can read a number of video formats. It writes to .AVI files, and you must select a video compression when writing -- or else VirtualDub produces uncompressed files, which are huge. There is information online on extensions to make VirtualDub save to MP4 files, but installation is tricky.
Deshaker corrects for horizontal and vertical shake, rotation and zoom, each adjustable separately. Deshaker's automatic border-fill option is very neat when it works. and has a "soften edges" option that makes the fill-in less noticeable. Deshaker can account for rolling shutter if the correct rolling shutter value is input, making a linear correction within each frame. Deshaker has an option to ignore pixels outside (or inside) a given area, useful to prevent undercorrection of a fisheye image. (The edges will then be overcorrected, as seen in the video above, but that is less annoying.) Deshaker also lets you change the image resolution during the stabilization process, possibly avoiding the need to process the video in another application.
Deshaker is a complex application with many settings, and I have a separate article on this site about it. Very specific custom settings are need for the best results with bicycling video.
Gooder Video SteadyHand is a free-standing commercial application, available either alone or in a package with two other apps, MotionPerfect – which you use to change the frame rate -- and SlowMotion, whose name describes it.
One thing I like about SteadyHand is that you can independently choose whether to stabilize against horizontal and vertical shake.
In my experience, the fixed-zoom mode of SteadyHand does not work correctly-- it produces a venetian blind effect in the picture. You can, however, turn zoom off and zoom the picture later in your editing app. This is preferable anyway, so you can also adjust panning to eliminate blank border areas.
You might as well buy the whole package. The MotionPerfect app converts between 25 and 30 frame per second video, or sets video to any other speed, by actually creating new images intermediate between the original ones (image interpolation). In this way, MotionPerfect avoids the jerkiness that is common with this conversion. The SlowMotion application works similarly, producing smooth slow motion. SteadyHand requires .AVI files as input, and so I use Handbrake (free) or the AVS4YOU software suite to run conversions. I use the DivX/Xvid MPEG-4 codec, which holds the file size down.
YouTube editing
YouTube is now offering online video editing tools including image stabilization. I've only tried this once, and it appears to work OK, but it isn't as feature-rich as SteadyHand or Deshaker.
There are some things which the software I know doesn't do but which would be nice.
Deshaker lets you preselect a zoom level so the software can reposition the image without reaching the borders of what was originally shot. I'd like to be able to adjust panning and zooming with keyframes, moving around in the image. Doing this without actually cropping the image would let the software use the entire original image to fill in borders. The software would stabilize based on the area selected. If the selection area and pan/zoom area were adjustable separately, then it would also be possible to avoid problems due to moving objects in the image. It would be nice also to pre-adjust rotation. A tilt of the head which is undetected while riding can be distracting in a video.
As a wide-angle image moves around, its perspective changes, as already described. Image-stabilization software could account for this, keeping the perspective constant.
Going further, software also could avoid the undercorrection/overcorrection problem with fisheye images.
The software would need the parameters of the lens as an input. To some extent, the software could figure this out for itself based on the input video.
This feature, to be sure, would slow processing significantly because it would require a sophisticated re-mapping of the image.
The Sony camera appears to have this capability.
This would apply different amounts of rolling-shutter compensation to different parts of the image, in either of two ways:
Last Updated: by John Allen