Ois report

Optical Image Stabilization Technology

Dept. of Electronics and Communication, HIT Nidasoshi 1

CHAPTER 1

INTRODUCTION

Image Stabilization (IS) technology has been considered essential to delivering improved image

quality in professional cameras. More recently, as a result of advancing technology, IS has become

increasingly popular to handheld device makers who want to propose high-end features for their

products. So, manufacturers like ST have worked hard on its technologies and methods for image

stabilization to significantly improve camera shutter speed and to offer precise suppression of camera

vibration. Today, from the technologic point of view, Digital Image Stabilization (DIS), Electronics

Image Stabilization (EIS) and Optical Image Stabilization (OIS) are the best understood and the

easiest to integrate in digital still cameras and smartphones, though they can produce different

image- quality results: in fact, DIS and EIS require large memory and computational resources on the

hosting devices, while OIS acts directly on the lens position itself and minimizes memory and

computation demands on from the host. As an electro-mechanical method, lens stabilization (optical

unit) is the most effective method for removing blurring effects from involuntary hand motion or

shaking of the camera.

Whether capturing still images or recording moving video, image stabilization will always be a

major factor in reproducing a near perfect digital replica. A lack thereof will result in image

distortion through pixel blurring and the creation of unwanted artifacts. While media capturing

devices such as digital cameras, digital camcorders, mobile phones, and tablets have decreased in

physical size, their requirements for pixel count density and resolution quality have increased

drastically over the last decade and will continue to rise. The market shift to compact mobile devices

with high megapixel capturing ability has created a demand for advanced stabilization techniques.

Two methods, electronic image stabilization (EIS) and optical image stabilization (OIS), are the most

common implementations.



CHAPTER 2

IMAGE STABILIZATION TECHNIQUES

There are two types of techniques

1. Optical image stabilization

2. Electronic image stabilization

2.1 OPTICAL IMAGE STABILIZATION:

An optical image stabilization system usually relies on gyroscopes or accelerometers to detect and

measure camera vibrations. The readings, typically limited to pan and tilt, are then relayed to

actuators that move a lens in the optical chain to compensate for the camera motion. In some designs,

the favored solution is instead to move the image sensor, for example using small linear motors.

Either method is able to compensate the shaking of camera and lens, so that light can strike the

image sensor in the same fashion as if the camera was not vibrating. Optical image stabilization is

particularly useful when using long focal lengths and works well also in low light conditions.

Optical image stabilization is used to reduce blurring associated with motion and/or shaking of the

camera during the time the image sensor is exposed to the capturing environment. However, it does

not prevent motion blur caused by movement of the target subject or extreme movements of the

camera itself, only the relatively small shaking of the camera lens by the user – within a few optical

degrees. This camera-user movement can be characterized by its pan and tilt components, where the

angular movements are known as yaw and pitch, respectively. Camera roll cannot be compensated

since 'rolling' the lens doesn't actually change/compensate for the roll motion, and therefore does not

have any effect on the image itself, relative to the image sensor.



2.2 ELECTRONIC IMAGE STABILIZATION:

EIS is a digital image compensation technique which uses complex algorithms to compare frame

contrast and pixel location for each changing frame. Pixels on the image border provide the buffer

needed for motion compensation. An EIS algorithm calculates the subtle differences between each

frame and then the results are used to interpolate new frames to reduce the sense of motion. Though

the advantage with this method is the ability to create inexpensive and compact solutions, the

resulting image quality will always be reduced due to image scaling and image signal post-

processing artifacts and more power will be required for taking additional image captures and for the

resulting image processing.

EIS systems also suffer when at full electronic zoom (long field-of-view) and under low-light

conditions. Electronic image stabilization, also known as digital image stabilization, has primarily

been developed for video cameras. Electronic image stabilization relies on different algorithms for

modeling camera motion, which then are used to correct the images. Pixels outside the border of the

visible image are used as a buffer for motion and the information on these pixels can then be used to

shift the electronic image from frame to frame, enough to counterbalance the motion and create a

stream of stable video.

Although the technique is cost efficient, mainly because there is no need for moving parts, it has one

shortcoming which is its dependence on the input from the image sensor. For instance, the system

can have difficulties in distinguishing perceived motion caused by an object passing quickly in front

of the camera from physical motion induced by vibrations.



CHAPTER 3

COMPARISON OF OIS & EIS TECHNIQUES

Fig.3.1 OIS and EIS Image Quality Comparison

Comparison to EIS, OIS systems reduce image blurring without significantly sacrificing image

quality, especially for low-light and long-range image capture. However, due to the addition of

actuators and the need for power driving sources compared to no additional hardware with EIS, OIS

modules tend to be larger and as a result are more expensive to implement.

EIS suffers when at full electronic zoom (Long field of view) and under low light conditions.

EIS requires large memory & computational resources on the hosting device compared to

OIS



CHAPTER 4

OIS BEHAVIOR

OIS is a mechanical technique used in imaging devices to stabilize the recording image by

controlling the optical path to the image sensor. The two main methods of OIS in compact camera

modules are implemented by either moving the position of the lens (lens shift) or the module itself

(module tilt).Camera movements by the user can cause misalignment of the optical path between the

focusing lens and center of the image sensor. In an OIS system using the lens shift method, only the

lens within the camera module is controlled and used to realign the optical path to the center of the

image sensor. In contrast, the module tilt method controls the movement of the entire module,

including the fixed lens and image sensor.

Module tilt allows for a greater range of movement compensation by the OIS system, with the largest

tradeoff being increased module height. Minimal image distortion is also achieved with module tilt

due to the fixed focal length between the lens and image sensor. Overall, in comparison to EIS, OIS

systems reduce image blurring without significantly sacrificing image quality, especially for low-

light and long-range image capture. However, due to the addition of actuators and the need for power

driving sources compared to no additional hardware with EIS, OIS modules tend to be larger and as a

result are more expensive to implement.

Fig.4.1 Main Methods of OIS Compensation



CHAPTER 5

OIS PRINCIPLE

Fig. 5.1 OIS compensation

The basic principle underlying OIS is simplified in Figure 5.1 where the movement effects are

amplified and represented on a single axis, for the sake of clarity. Let’s suppose we take a picture of

a non-moving object in which the shutter remains open for a time interval equal to ∆t; if no

compensation occurs (Figure a), the involuntary rotation of the camera generates a distribution of the

light cone, over a single pixel, splattered on a segment indicated in Figure a by A-B. Clearly, this

phenomenon occurs across the whole image sensor, causing a blurred image.

Otherwise, when optical stabilization occurs (Figure b), the lens moves opposite to the direction of

the camera shake and the image results to be stabilized (i.e. the subject acquired in t1 coincides with

image acquired in t 0).



CHAPTER 6

BLOCK DIAGRAM OF OIS

Fig. 6.1 OIS High level block diagram.

Blur due to hand jitter is reduced by mechanically stabilizing the camera. A two axis gyroscope is

used to measure the movement of the camera, and a microcontroller directs that signal to small linear

motors that move the image sensor, compensating for the camera motion. Other designs move a lens

somewhere in the optical chain within the camera. A typical high-level block diagram. With either

method, the result is that the body of the camera may shake, but light strikes the pixels of the image

sensor as though the camera were not shaking.



1) Sensor Requirements:

For an OIS system to function properly, the sensors, actuators, and electronics must be carefully

chosen. A newcomer to this field may immediately wonders why gyroscopes are used in image

stabilization, rather than other sensors, such as accelerometers. A gyroscope Measures the rotation

about an axis, where rotations about X, Y, and Z axes for a given Object are referred to as roll, pitch,

and yaw.

2) Gyroscopes:

Gyroscopes are employed in IS systems to sense pitch and yaw with low noise and high sensitivity in

order to resolve the small movements associated with hand jitter. Typically, these systems require a

full-scale range of +/-30 degrees per second, with at least 10-bit resolution.

3) Actuator Requirements:

Actuators for OIS systems must be small, low-power, and accurate for tiny movements. The range of

movement required by an OIS actuator depends on the optics of the system, but the desired outcome

is an ability to compensate for ±1º of rotation. The most common actuator is the voice coil, an

electromagnetic linear motor, used to drive the lens.



CHAPTER 7

ADVANTAGES & DISADVANTAGES

7.1 ADVANTAGES

OIS systems reduce image blurring without significantly sacrificing image quality, especially

for low-light and long-range image capture.

Optical Image Stabilization technology is an effective solution for minimizing the effects of

involuntary camera shake or vibration.

Optical image stabilization directly acts on the lens position itself it reduces memory

requirement.

Optical image stabilization minimizes computational resources on the hosting device.

7.2 DISADVATAGES

Two main challenges in the development of OIS in smartphones and digital cameras are size

and cost. The additional hardware required to implement OIS it increases the total cost of

camera, and increases the camera’s size.



CHAPTER 8

APPLICATIONS

Smartphones: The introduction of optical Image Stabilization in several mobile platforms

has been a significant added value for photography lovers and especially for younger users,

who replaced their traditional and bulky cameras with brand-new smartphones—or had

cameras available to record memories simply because those cameras were embedded in the

mobile platform they were already carrying.

Digital cameras: Optical Image Stabilization technology is an effective solution for

minimizing the effects of involuntary camera shake or vibration in digital cameras. It senses

the vibration on the hosting system and compensates for these camera movements to reduce

hand-jitter effects.



CONCLUSION

Gyroscope-based optical and electronic image stabilization systems are mature and proven

technologies that address the quality of images. OIS has been penetrating the DSC market rapidly,

and as camera resolutions continue to increase, optical image stabilization is expected to become as

standard a function as autofocus on every DSC. As engineers struggle to pack advanced technologies

into the scarce and premium real estates of handsets, small size and low cost are at the top of their

lists. With the fast pace of increased CMOS sensors pixel densities and feature offerings, such as

auto focus and optical zoom, OIS entered into the camera phone market as a prominent feature.



REFERENCES

1. Seung-Kwon Lee, Jin-Hyeung Kong, ―An Implementation of Closed-loop Optical Image

Stabilization System for Mobile Camera‖, Dongwoon Anatech. Co. Ltd., Kwangwoon

University, 2014.

2. L. K. Lai, T. S. Liu, ― DESIGN OF AUTO-FOCUSING MODULES IN CELL PHONE

CAMERAS ―, Department of Mechanical Engineering, National Chiao Tung University,

Hsinchu 30010, Taiwan, INTERNATIONAL JOURNAL ON SMART SENSING AND

INTELLIGENT SYSTEMS VOL. 4, NO. 4, DECEMBER 2011.

3. Paresh Rawat, Jyoti Singhai, ― Review of Motion Estimation and Video Stabilization

techniques for hand held mobile video ‖, Signal & Image Processing : An International

Journal (SIPIJ) Vol.2, No.2, June 2011.

4. Kazuki NISHI, Tsubasa ONDA, ― EVALUATION SYSTEM FOR CAMERA SHAKE AND

IMAGE STABILIZERS ‖, The University of Electro-Communications, Tokyo 182-8585,

Japan, IEEE, ICME 2010.

Date post:	17-Aug-2015
Category:	Engineering
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