Image stabilization is a family of techniques used to reduce blurring
associated with the motion of a camera or other imaging device during exposure.
Generally, it compensates for pan and tilt of the imaging device, although
electronic image stabilization can also be used to compensate for rotation. It
is used in image-stabilized binoculars, still and video cameras, astronomical
telescopes, and also smartphones, mainly the high-end. With still cameras, camera
shake is particularly problematic at slow shutter speeds or with long focal
length lenses. With video cameras, camera shake causes visible
frame-to-frame jitter in the recorded video. In astronomy, the problem of
lens-shake is added to by variations in the atmosphere over time, which will
cause the apparent positions of objects to change.
Application in still photography In photography, image stabilization can
often permit the use of shutter speeds 2–4.5 stops slower, although even slower
effective speeds have been reported. The rule of thumb to determine the
slowest shutter speed possible for hand-holding without noticeable blur due
to camera shake is to take the reciprocal of the 35 mm equivalent focal
length of the lens, also known as the "1/mm rule". For example, at a focal
length of 125 mm on a 35 mm camera, vibration or camera shake could affect
sharpness if the shutter speed was slower than 1/125 second. As a result of
the 2–4.5 stops slower shutter speeds allowed by IS, an image taken at 1/125
second speed with an ordinary lens could be taken at 1/15 or 1/8 second with an
IS-equipped lens and produce almost the same quality. The sharpness obtainable
at a given speed can increase dramatically. When calculating the
effective focal length, it is important to take into account the image format a
camera uses. For example, many digital SLR cameras use an image sensor that is
2/3, 5/8, or 1/2 the size of a 35 mm film frame. This means that the 35 mm
frame is 1.5, 1.6, or 2 times the size of the digital sensor. The latter values
are referred to as the crop factor, field-of-view crop factor, focal-length
multiplier, or format factor. On a 2x crop factor camera, for instance, a 50
mm lens produces the same field of view as a 100 mm lens used on a 35 mm film
camera, and can typically be handheld at 1/100 of a second.
However, image stabilization does not prevent motion blur caused by the
movement of the subject or by extreme movements of the camera. Image
stabilization is only designed for and capable of reducing blur that results
from normal, minute shaking of a lens due to hand-held shooting. Some lenses
and camera bodies include a secondary panning mode or a more aggressive
'active mode', both described in greater detail below under optical image
stabilization. Image-stabilization features can also be
a benefit in astrophotography, when the camera is technically—but not
effectively—fixed in place. The Pentax K-5 and K-r can use their sensor-shift
capability to reduce star trails in reasonable exposure times, when equipped
with the O-GPS1 GPS accessory for position data. In effect, the
stabilization compensates for the Earth's motion, not the camera's.
There are two types of implementation - lens-based, or body-based stabilization.
These refer to where the stabilizing system is located. Both have their
advantages and disadvantages. Techniques
= Optical image stabilization= An optical image stabilizer, often
abbreviated OIS, IS, or OS, is a mechanism used in a still camera or
video camera that stabilizes the recorded image by varying the optical
path to the sensor. This technology is implemented in the lens itself, or by
moving the sensor as the final element in the optical path. The key element of
all optical stabilization systems is that they stabilize the image projected
on the sensor before the sensor converts the image into digital information.
Different companies have different names for the OIS technology, for example:
Vibration Reduction - Nikon camera in 1994)
Image Stabilizer - Canon in 1995. In 2009, they introduced their first lens
utilizing their 4-axis Hybrid IS.) AntiShake - Konica Minolta
IBIS - In Body Image Stabilisation - Olympus
Optical SteadyShot - Sony MegaOIS, PowerOIS - Panasonic and Leica
SteadyShot, Super SteadyShot, SteadyShot INSIDE - Sony
Optical Stabilization - Sigma Vibration Compensation - Tamron
Shake Reduction - Pentax PureView - Nokia
UltraPixel - HTC or HTC Butterfly S which also have UltraPixel)
Most of high-end smartphones as of late 2014 use Optical Image Stabilization for
photos and videos. Lens-based
In Nikon and Canon's implementation, it works by using a floating lens element
that is moved orthogonally to the optical axis of the lens using
electromagnets. Vibration is detected using two piezoelectric angular velocity
sensors, one to detect horizontal movement and the other to detect
vertical movement. As a result, this kind of image stabilizer corrects only
for pitch and yaw axis rotations, and cannot correct for rotation around the
optical axis. Some lenses have a secondary mode that counteracts vertical
only camera shake. This mode is useful when using a panning technique, and
switching into this mode depends on the lens; sometimes it is done by using a
switch on the lens, or it can be automatic.
Mainly for using video while walking to compensate jitter, Panasonic introduced
Power Hybrid O.I.S + with 5-axis correction: axis rotation, horizontal
rotation, vertical rotation, horizontal and vertical.
Some of Nikon's more recent VR-enabled lenses offer an 'Active Mode' that is
intended to be used when shooting from a moving vehicle, such as a car or boat,
and should correct for larger shakes than the 'Normal Mode'. However, Active
Mode, when used under normal shooting conditions, can result in poorer results
than the 'Normal Mode'. This is because active mode is optimized for reducing
higher angular velocity movements, where normal mode tries to reduce lower
angular velocity movements over a larger amplitude and timeframe.
Most manufacturers suggest that the IS feature of a lens be turned off when the
lens is mounted on a tripod as it can cause erratic results and is generally
unnecessary. Many modern image stabilization lenses are able to
auto-detect that they are tripod-mounted and disable IS automatically to prevent
this and any consequent image quality reduction. The system also draws power
from the battery, so deactivating it when it is not needed will extend the
time before a recharge is required. One of the main disadvantages about
lens-based image stabilization is the higher price tag that comes with it;
image stabilization has to be paid for each lens anew. Also, not every lens is
available as an image-stabilized variant. This is often the case for fast
primes and wide-angle lenses. While the most obvious advantage for image
stabilization lies with longer focal lengths, even normal and wide-angle
lenses benefit from it in low-light applications.
Lens based stabilization also has advantages over in-body stabilization.
In low-light or low-contrast situations, the autofocus system is able to work
more accurately when the image coming from the lens is already stabilized. In
cameras with optical viewfinders, the image seen by the photographer through
the stabilized lens reveals more detail because of its stability, and it also
makes correct framing easier. This is especially the case with longer
telephoto lenses. This advantage does not occur on compact system cameras,
because the sensor output to the screen or electronic viewfinder would be
stabilized. Sensor-shift
The sensor capturing the image can be moved in such a way as to counteract the
motion of the camera, a technology often referred to as mechanical image
stabilization. When the camera rotates, causing angular error, gyroscopes encode
information to the actuator that moves the sensor. The sensor is moved to
maintain the projection of the image onto the image plane, which is a
function of the focal length of the lens being used. Modern cameras can
automatically acquire focal length information from modern lenses made for
that camera; in a few cases, a chip can be retrofitted to a lens allowing the
focal length to be communicated. Konica Minolta used a technique called
AntiShake now marketed as SteadyShot in the Sony α line and Shake Reduction in
the Pentax K-series and Q series cameras, which relies on a very precise
angular rate sensor to detect camera motion. Olympus introduced image
stabilization with their E-510 D-SLR body, employing a system built around
their Supersonic Wave Drive. Other manufacturers use DSPs to analyze the
image on the fly and then move the sensor appropriately. Sensor shifting is
also used in some cameras by Fujifilm, Samsung, Casio Exilim and Ricoh Caplio.
The advantage with moving the image sensor, instead of the lens, is that the
image can be stabilized even on lenses made without stabilization. This may
allow the stabilization to work with many otherwise-unstabilized lenses, and
reduces the weight and complexity of the lenses. Further, when sensor-based image
stabilization technology improves, it requires replacing only the camera to
take advantage of the improvements, which is typically far less expensive
than replacing all existing lenses if relying on lens-based image
stabilization. Some sensor-based image stabilization implementations are
capable of correcting camera roll rotation, a motion that is easily
excited by pressing the shutter button. No lens-based system can address this
potential source of image blur. A by-product of available "roll"
compensation is that the camera can automatically correct for tilted
horizons in the optical domain, provided it is equipped with an electronic spirit
level, such as the Pentax K-7/K-5 cameras.
One of the primary disadvantages of moving the image sensor itself is that
the image projected to the viewfinder is not stabilized. However, this is not an
issue on cameras that use an electronic viewfinder, since the image projected on
that viewfinder is taken from the image sensor itself. Similarly, the image
projected to a phase-detection autofocus system, if used, is not stabilized.
Some, but not all, camera-bodies capable of in-body stabilization can be pre-set
manually to a given focal length, and their anti-shake will correct as if that
focal length lens is attached, allowing older lenses and lenses from other
makers to be stabilized. This isn't viable with zoom lenses, whose focal
length is variable. Some adapters will communicate focal length information
from the maker of one lens to the body of another maker. Some lenses that do
not report their focal length can have a chip added to the lens, which will
report a pre-programmed focal-length to the camera body. Sometimes, none of
these techniques is viable, and image-stabilization simply cannot be
used with such lenses. In-body image stabilization requires the
lens to have a larger output image circle because the sensor is moved
during exposure and thus uses a larger part of the image. Compared to lens
movements in optical image stabilization systems the sensor movements are quite
large, so the effectiveness is limited by the maximum range of sensor movement,
where a typical modern optically stabilized lens has greater freedom. The
required sensor movement increase with the focal length of the lens being used,
making sensor-shift technology less suited for very long telephoto lenses,
especially when using slower shutter speeds because the available motion
range of the sensor quickly becomes insufficient to cope with the increasing
image displacement. = Digital image stabilization=
Real-time digital image stabilization—also called electronic
image stabilization -- is used in some video cameras. This technique shifts the
electronic image from frame to frame of video, enough to counteract the motion.
It uses pixels outside the border of the visible frame to provide a buffer for
the motion. This technique reduces distracting vibrations from videos by
smoothing the transition from one frame to another. This technique does not
affect the noise level of the image, except in the extreme borders when the
image is extrapolated. It cannot do anything about existing motion blur,
which may result in an image seemingly losing focus as motion is compensated.
Some still camera manufacturers marketed their cameras as having "digital image
stabilization", when they really only had a high-sensitivity mode giving a
short exposure time, resulting in pictures with less motion blur, but more
noise. It will reduce blur when photographing something that is moving,
as well as from camera shake. Others are now also using digital signal
processing to reduce blur in stills, for example by sub-dividing the exposure
into several shorter exposures in rapid succession, discarding blurred ones,
re-aligning the sharpest sub-exposures and adding them back together again.
= Stabilization filters= Many video non-linear editing systems
use stabilization filters that can correct a non-stabilized image by
tracking the movement of pixels in the image and correcting the image by moving
the frame. The process is similar to digital image stabilization but since
there is no larger image to work with the filter either crops the image down
to hide the motion of the frame or attempts to recreate the lost image at
the edge through spatial or temporal extrapolation.
Online services, including Google's YouTube, are also beginning to provide
video stabilization as a post-processing step after content is uploaded. This has
the disadvantage of not having access to the realtime gyroscopic data, but the
advantage of more computing power and the ability to analyze images both
before and after a particular frame. = Orthogonal transfer CCD=
Used in astronomy, an orthogonal transfer CCD actually shifts the image
within the CCD itself while the image is being captured, based on analysis of the
apparent motion of bright stars. This is a rare example of digital stabilization
for still pictures. An example of this is in the upcoming gigapixel telescope
Pan-STARRS being constructed in Hawaii. = Stabilizing the camera body=
A technique that requires no additional capabilities of any camera body–lens
combination consists of stabilizing the entire camera body externally rather
than using an internal method. This is achieved by attaching a gyroscope to the
camera body, usually utilizing the camera's built-in tripod mount. This
allows the external gyro to stabilize the camera, and is typically employed in
photography from a moving vehicle, when a lens or camera offering another type
of image stabilization is not available. This has been integrated into camcorders
by allowing the sensor and lens assembly to move together within the camera
housing. Another technique for stabilizing a
video or motion picture camera body is the Steadicam system, which isolates the
camera from the operator's body using a harness and a camera boom with a
counterweight. = Camera stabilizer=
A camera stabilizer is any device or object that is used to externally
stabilize the camera. This could be a Steadicam, a tripod, the camera
operator's hand, or anything in-between. In close-up photography, using rotation
sensors to compensate for changes in camera-pointing-direction becomes
insufficient. Moving, rather than tilting, the camera up/down or
left/right by a fraction of a millimeter becomes noticeable if you are trying to
resolve millimeter-size details on the object. Linear accelerometers in the
camera, coupled with information such as the lens focal length and focused
distance, can feed a secondary correction into the drive that moves the
sensor or optics, to compensate for linear as well as rotational shake.
In biological eyes In many animals, including human beings,
the inner ear functions as the biological analogue of an accelerometer
in camera image stabilization systems, to stabilize the image by moving the
eyes. When a rotation of the head is detected, an inhibitory signal is sent
to the extraocular muscles on one side and an excitatory signal to the muscles
on the other side. The result is a compensatory movement of the eyes.
Typically eye movements lag the head movements by less than 10 ms.
See also Adaptive optics
Heligimbal Shaky camera
Hyperlapse Deblurring
Motion compensation References