01 lens & sensor technology 20130123

Lens and Image Sensor
Technology
Release department: ICB MKT | AVer Information Inc. | www.aver.com | 2013-01-23

Internal Only (including branch offices)

Agenda

• Lens Technology
– Lens & Mounting
– Lens Types
– Focal Length, Aperture, Depth of Field & View Angle
– Lens vs. IR Light

• Sensor Technology
– CMOS vs. CCD
– Interlaced vs. Progressive

• Lighting vs. Image Quality
– Shutter vs. Gain Control
– Denoise
– Backlight Compensation vs. Wide Dynamic Range
– Other factors affecting image quality
© AVer Information Inc.

Lens Technology


Image Processing

SoC CPU
DSP for WLAN or
Image (video/audio
Lens Image Ethernet/ LAN/
Sensor compression)
processing PoE Internet
Flash DRAM
128MB 128/256MB

Capturing Encoding Streaming
Light (optical image) The processed video is Images are transmitted
passes through the compressed by a Digital Signal in a single or multiple
lens and falls on the Processing (DSP) to achieve a streams in pre-set
sensor that converts smaller data size for optimal resolution, frame rate
it into electrical transmission. Signals can be and image quality via
signals (where compressed and encoded into an Ethernet cable to
cropping of ePTZ H.264 / MJPEG / MPEG-4 the remote site via
images take place; or formats. LAN or Internet.
some in SoC)

Camera Lens
Camera Lens is the fundamental component that determines
image quality
• Factors affecting image quality
• light source of the environment
• Lens
• Sensor
• compression engine
• bandwidth
• Most Box type IP cameras are designed to adapt interchangeable external
lenses to allow system installers to select and purchase lens that best fits
their specific needs


Lens Technology

Lens & Mounting


Lens Mount Type
Some lens mounts enables the interchange of external lens
• Board-mount – lens is not interchangeable and is mounted directly on
the circuit board. They are less versatile and can be very small (M12,
M14 or M19). For example, bullet, dome and fisheye cameras.
• C-mount – 17.526mm FFD (more expensive)
• CS-mount – 12.5mm FFD; mostly ≥ 2M (cheaper)
*FFD stands for flange focal distance (i.e. distance between lens mount and sensor)
*Speed domes use zoom lens modules

Board-mount lens C-mount lens CS-mount lens

C-mount vs. CS-mount Lenses
Box type cameras can support both C-mount and CS-mount
lenses with the use of C-ring (5mm spacer ring)

Lens Type C-mount CS-mount
Camera Type FFD 17.526mm FFD 12.5mm

C-mount yes no

Camera C/CS-mount yes yes

manufacturer’s
CS-mount C-ring yes tuning ring


CS-mount Camera vs. C-mount Lens

The use of adapter ring helps to get the image into focus

light rays
light rays

C-mount lens C-mount lens

C-ring
17.526mm 17.526mm
Image out
of focus
sensor sensor

CS-mount camera CS-mount camera

C/CS-mount Camera vs. C-mount Lens
Sometimes with the use of the adapter ring, because of the difference in the
distance between the lens and the sensor, the image quality may be affected.
C/CS-mount cameras come with built-in flange-back adjustment ring that can
adjust the distance between the lens and the sensor with a switch.

C-mount lens

Flange-back
sensor adjustment
sensor
ring
Adjustable C/CS-mount camera
*Some advanced IP cameras can remotely adjust the back focus.

Lens Form Factor vs. Sensor
sensor size 1/4” 1/3” 1/2.5” 1/2“
diagonal 4mm 6mm 7.18mm 8mm
width 3.2mm 4.8mm 5.76mm 6.4mm
height 2.4mm 3.6mm 4.29mm 4.8mm
Sensor sizes are specified by its diagonal length. Sensor size given in inches
employs sensor’s outer glass diagonal as a base, not a real diagonal.

1/4” lens & 1/3” sensor 1/3” lens & 1/3” sensor 1/2” lens & 1/3” sensor
The field of view (FOV) Lens size matches with The angle of view of the
is narrower with black the sensor = optimized lens is not fully utilized
corners image quality
*Example: If an IP camera adapts a 5M sensor with a 3M lens, the image quality may
be similar to that of a 2.5M IP camera.

Lens Technology

Lens Types


Types of Lens
Fixed lens
Lens with constant focal length
that cannot be adjusted fixed lens
adjust tele/wide

Vari-focal lens
Lens with adjustable focal
length and manual focus is vari-focal lens
required

Zoom lens
Subtype of vari-focal lens and
some zoom lenses come with
the auto focus feature, such as
speed domes. zoom lens


Lens with Fixed / Manual Iris
Iris is used to control the light level to the image sensor, ensuring the image is sharp,
clear and correctly exposed with good contrast and resolution.

Fixed iris
The size of the iris cannot be adjusted and is a look at the iris
suitable for indoor applications where the light
level is constant. The camera can compensate
for changes in the level of light by adjusting the
exposure time or using gain.
Source: ACTi

Manual iris Fixed iris lenses
can be manually adjusted the iris size and is
used in stable lighting conditions. (Unlike the
auto-iris lenses, its lens does not have a cable.)

Manual iris lens

Lens with Auto Iris
Auto-iris
There are 2 types of auto-iris lenses: DC-drive iris and
video-drive iris. Both are motor-driven with auto-
adjustable iris openings that responds to changes in light
levels. They are recommended for use in inconsistent
lighting conditions (e.g. outdoors). However, the control
cannot be made available to the camera or user.
DC-drive iris lens
DC-drive iris
The iris opening is controlled via DC current with drive
circuit inside the camera
Video-drive iris
The iris opening is controlled with drive circuit built in
the lens (mostly used in analog cameras) Video-drive iris lens


Lens with Auto Iris – P-iris
P-iris (Precise Iris)
P-iris lens is to be a replacement of DC-drive iris that it uses
a motor which allows the position of the iris opening to be
precisely controlled. Together with software that is
configured to optimize the performance of the lens and
image sensor, it automatically provides the best iris position
for optimal image quality in all lighting conditions. motor inside

It provides improvements in contrast, clarity, resolution and P-iris lens
depth of field, and is ideal for the monitoring of long
corridor or parking lot.
Prevailing scenario: In bright situations, P-Iris limits the closing of the iris to avoid
blurring (diffraction) caused when the iris opening becomes too small. This can
typically happen in cameras that use DC-iris lenses in combination with megapixel
sensors that have small pixels.

Lens Technology

Focal Length, Aperture,
DOF & View Angle


Focal Length (f) vs. F-number (F/no)
camera sensor lens
light
Focal Length (f)
distance between focal point (sensor)
and optical center (lens)
for example: f=3~9mm optical
focal point
center
focal length

F-number (F/no)
(a.k.a. F-stop or relative aperture) aperture
the amount of light getting through the iris
aperture, controlled by the sizing of an
iris
focal length (f) iris
F/no = retina
diameter of the aperture (mm) pupil (aperture – (sensor)
or iris size opening of the iris)

lens

Depth of Field (DOF)
DOF is a range of distance in which object is acceptably sharp
and can be adjusted by sizing the iris (aperture)

Depth of Field = Front Depth of Field + Rear Depth of Field

Front DOF is the distance in front the object that is acceptably sharp
Rear DOF is the distance behind the object that is acceptably sharp

front depth of field
rear depth of field
focal depth
Depth of Field

Focal depth is the distance over which the sensor can be displaced
while the object stays acceptably sharp.

Depth of Field – Applications
Depth of Field F/no Iris Size focal length (f)
short Small (F1.2) large F/no =
diameter of the aperture (mm)
long Large (F22) small or iris size

smaller F/no bigger F/no
Applications: Applications:
• Tollgate (license plate) • office space / passageways
• front door / courtyard (where the • outdoor parking lot
record of passersby is not allowed) • 24hrs outdoor surveillance

Depth of Field – Adjusting Focus
When a camera is installed at day time, the iris size is usually set to small
(longer DOF). A camera with auto iris will auto adjust at night to allow more
light to come through, thus decreasing the DOF. If the focus was not adjusted
to its best position, the blurring effect will be even more obvious at night time.

depth of field depth of field
DAY NIGHT

ideal focus position ideal focus position
adjusted focus position adjusted focus position


Angle of View
The shorter the focal length or
the larger the sensor, the bigger FOV
the angle of view.
• It can be measured horizontally (image shorter focal length
width) and vertically (image height) or
diagonally (a.k.a. Field of View, FOV)

Tele vs. Wide angle of view lens sensor
97.9°(W)~23.6°(T) (vertical)
Tele (T) – minimum angle of view
Wide (W) – maximum angle of view

longer focal length

Lens Technology

Lens vs. IR Light


IR-Cut Filter Removable (ICR)
Infrared (IR) Light
Though it is not visible to the human eye,
may downgrade image quality during
day-time by distorting colors; however, it
can be used to improve visibility under
low lightening conditions.

ICR adjusts infrared light access to the camera
• Digital ICR
a digital filter and the performance is not very impressive

• Mechanical ICR
a mechanical shutter placed between the camera sensor and the lens, that is
controlled by a motor or an electromagnet


ICR (Day / Night)

Day-time
ICR removed ICR on

It blocks infrared light and allows only visible light to pass through

Night-time
or
low lighting ICR on ICR removed

ICR is disabled/removed and the live the image will become
black & white, which is more sensitive to infrared light
* However, the image may be blurred and can be adjusted with an IR corrected lens.

IR Corrected Lens
Since visible light is composed of lights of various wavelengths, with a single
lens, light is bent in the same way as with a prism and the focal lengths of
lights with different wavelengths vary. As a result, not all light rays reach the
same point (focal point), which causes chromatic aberration.

IR Corrected Lens (type of Chromatic Lens)
The purpose is to compensate for the focus shift by
matching the focal lengths of two different
wavelengths (e.g. visible & IR lights) to reduce the
chromatic aberration to a certain extent. However,
lights of other wavelengths have different focal
lengths and result in residual chromatic aberration,
which is known as the secondary spectrum.
image source:
Microscopy Resource Center

Extra-low Dispersion (ED) Lens (色散)
Extra-low Dispersion Glass (ED Lens)
It a more a expensive and higher-quality glass that reduces chromatic
aberrations, or optical color defects (fringing) to a remarkable degree thus
helps the lens to always stay in focus. It is most suitable for day & night and
those with telephoto lens IP cameras.

image source: Nikon

Sensor Technology


What is a Sensor?
Sensor is a camera component converting optical image into electrical signal.
It is made up of many photo-sites and each photo-site corresponds to a picture
element (pixel). Each pixel registers the amount of light it is exposed to and
converts it into a corresponding number of electrons. The brighter the light,
the more electrons are generated.
Sensor Type
CCD CMOS
– higher power consumption + low power consumption
– more expensive (Japanese + cheaper
patents) + more integration possibilities & functions

It should be noted that sensor technology is evolving
dynamically and the differences between both sensor
types are becoming smaller. This is why both types
should be considered a potential choice in the future.

Scanning
Scanning is a process of building image by camera sensor as
well as displaying it by monitors and TVs.

Interlaced Scanning

+

odd lines even lines

Progressive scanning


Interlaced Scanning
Interlaced scanning
 two fields of lines are been processed at the same time: a field displaying
the odd lines, and a second field displaying the even lines
 only half the number of lines (alternating between odd and even lines) of
an image is sent at a time, which reduces the use of bandwidth by half
 may creates artifacts or distortions as a result of ‘missing’ data (though
not noticeable on interlace monitors)

+ =
odd lines even lines distorted image or blurred actual image
*1080i represents 1080 lines interlaced; 720i does NOT exist.

Progressive Scanning
Progressive scanning (*all IP cameras adopt progressive CMOS cameras)
 values are obtained for each pixel on the sensor and image data is scanned
sequentially line by line, producing a full frame image
 entire image frame can be sent over a network but requires higher bandwidth
 best for presenting moving objects

*720p represents 720 lines progressive; 1080p represents 1080 lines progressive

Lighting vs. Image Quality



Shutter vs. Gain Control


Exposure
Exposure of an image refers to the amount of light that falls
on an image sensor
• exposure is dependant upon the shutter speed and aperture
• longer exposure time produces better image in low lighting conditions,
however it is susceptible to motion blur
• shorter exposure time is recommended for capturing fast movement

The exposure settings of an IP
camera includes
• gain control
• shutter speed
• usually the iris size / aperture is not
configurable

Auto Gain Control
Gain control is basically a form of amplification where the
camera will boost the image received so the object can be
seen more clearly and is critical in low lighting conditions

Automatic Gain Control (AGC)
• auto amplifies video signal when its strength falls below minimal value
• as the image gets brighter, more noise is produced
• as gain increases, the bandwidth consumption increases, and CBR or VBR
with a bandwidth cap can be applied to minimize the negative side effects
 video loss or missing pixels

Denoise features can help to reduce the noise as well as reduce
the bandwidth consumption
*a.k.a. ISO value in optical

Auto Electronic Shutter (AES)
A camera’s shutter determines when the camera sensor will
be open or closed to the incoming light (exposure time)

Shutter Speed
The duration that light is permitted to enter the camera
and is usually described using fractions of seconds (e.g.
1/30s, 1/300s). Quick shutter results
in short exposure time
Auto Electronic Shutter (AES)
It is used in IP cameras where the iris remains fixed,
allowing the shutter speed to automatically adjust
exposure according to lighting conditions to keep the
signal output at the best possible level. Slow shutter results in
long exposure time

Rolling Shutter
Rolling shutter is a method of image rolling shutter exposure control
acquisition in which each frame is recorded
reset
by scanning across the frame either
vertically or horizontally and not all parts of
the image are recorded at exactly the same
time, even though the whole frame is
displayed at the same time during playback.
readout Inte-
gration
Pros: It allows the image to have a more time
reset
organic (filmic) effect look.

Cons: This produces predictable distortions
of fast-moving objects or when the sensor readout Inte-
captures rapid flashes of light. gration
reset time
Source: Wiki & Aptina

Global Shutter
Global shutters is an alternative method global shutter exposure control
of image acquisition where pixels in the
imaging array are exposed all at once. reset all
pixels
Pros: The image is not likely to appear
distorted.

Cons: The use of global shutter pixel
all pixels
requires the addition of a pixel-level integrating
memory.

all pixels stop
integration and
commence
readout
Source: Aptina

Global vs. Rolling Shutter

Source: Aptina

click to watch the video at
http://www.youtube.com/watch?v
=R-h46Zz9YZQ


Auto Iris vs. AES

Auto Iris AES

technology optical electronic

controls the amount controls the duration
function
of light exposed to sensor sensor is exposed to light

reaction to
slower quicker
lighting change

eliminate smearing effect
advantage faster to adjust exposure level
(拉光)

cost high moderate


Illumination (lux)
Illumination (measures in lux) is the intensity of light hitting
a surface as seen by a human eye (i.e. the brightness of a place)
1 lumen (light emission unit)
1 lux =
1 m2 (surface unit)

Recording Conditions Illumination Level
sunset 500 lux
twilight 1 lux
night w/ full moon 0.1 lux
night w/ quarter of the lunar disk 0.01 lux
night w/ a clear starry sky 0.001 lux



Denoise


Noise Reduction
3D & 2D noise reduction (denoise)
Technology to provide clearer video with less noise under poor lighting
conditions and dramatically reduces the storage capacity for backend
encoding through an improved, cleaner signal.

Method
3D denoise 2D denoise
Difference
analyzes successive pictures to
technology detect and adjust for noise analyzes only a single picture
over a span of time
can dramatically reduce noise can maintain smooth edges on
pros
on the image moving objects
moving objects will show with
cons the effect is limited
motion blur


Dynamic Noise Reduction
Dynamic 3D / 2D noise reduction (denoise)
Features advanced automated 3D and 2D denoise adjustment to deliver
cleaner, sharper images even in low lighting conditions and greater storage
efficiency

3D denoise
motion

2D vs. 3D
denoise

*3D noise reduction is achieved by
comparing noise level of continuous frames


Backlight Compensation
vs. Wide Dynamic Range


Backlight Compensation (BLC)
When bright lighting that originates behind a subject of interest, it will lead to
the underexposing (silhouetting) of the main subject. BLC is a mechanism
designed to adjust the exposure of the entire image to properly expose the
subject in the foreground.

Scenario
inside bank lobby
Since BLC tries to ignore small areas of high BLC on
illumination to ensure the larger portion of the scene
remains bright, the area of interest would have the
same exposure regardless of the background (people
passing by on the street outside of the bank).

BLC off


Wide Dynamic Range (WDR)
WDR is a more effective alternative to BLC because it can
handle multiple exposure zones to give both the highlight
and low light areas a proper exposure.

Digital WDR (D-WDR) short exposure

It is a software-based technique that optimizes the image +
quality by maintaining the original exposure value while
adjusting the gamma y value to enhance the dark areas.

True WDR long exposure
It is accomplished by using 2 shutters (or more – multi-
frame imaging) to capture the same image with both short
and long exposures may cut the frames by half.

© AVer Information Inc. result

WDR Applications

an indoor premise where light having the IP camera pointing
enters from various angles (intense towards a window or an entrance
sunlight or artificial light), such as a door and the background is washed
multi-window room, e.g. airport, out during daytime, e.g. restaurant,
train station, shopping mall, et al. stores with big glass windows, et al.

BLC vs. WDR
technology
True WDR Digital WDR BLC
item

shutter needed 2 or more 1 1

combine frames of adjust the gamma y adjust the exposure
technology long and short value to enhance of the entire image
exposures the dark area
good image quality comparatively good object of interest is
pros image quality and clear
lower in cost
may have minor minor image washed overexposure in
color restoration out problem brightly lighted
cons problem or color areas, resulting in
dispersion the loss of pertinent
information



Other factors affecting
image quality


Color Temperature
Color temperature

intensity
relative
describes the spectrum
of light which is radiated
from a "blackbody“ – an
400 450 500 550 600 650 700
object that absorbs all wavelength
incident light.
color temperature light source
(Kelvin)
The color temperature of
1000~2000K candlelight
a light source refers to 2500~3500K tungsten bulb (household variety)
the relative warmth or 3000~4000K sunrise/sunset (clear sky)
coolness of the white 4000~5000K fluorescent lamps
light. 5000~5500K electronic flash
5000~6500K daylight with clear sky (sun overhead)
6500~8000K moderately overcast sky
9000~10000K shade or heavily overcast sky
© AVer Information Inc. Source: Cambridge in Colour

White Balance
The white balance function is designed to remove unrealistic color cast from
the image and compensate for hue shifts by adjusting color balance in relation
to white color.

Automatic White Balance (AWB)
The white balance is adjusted automatically. However, white or bright
colorless element is needed for proper calibration, otherwise color abundance
may be mistaken for color cast. This function is best suited for environments
with no light source changes (e.g. between incandescent and fluorescent
lights).

Manual White Balance (MWB)
The white balance is adjusted manually and can be more precise when
capturing image rich in colors.


Color Rolling (色飄)
Cause:
When the frequencies of the camera shutter and light source do not match,
camera may have problems with adjusting the white balance. As a result,
consecutive color shifts occur. Typically seen with fluorescent lightings
(flicker, 50/60Hz).

Solution:
It can be solved by matching shutter speed with light source frequency 
50Hz vs. 1/50s or 60Hz vs. 1/60s

* Only analog cameras has this problem

Blooming (暈光)
Cause:
It is when strong light or backlight that causes the sensor to be overcharged
and some pixels will overflow to pixels nearby, resulting in blurred halos
surrounding the objects.

Solution:
Sometimes it can be solved by adjusting the exposure settings.

Scenario:
- when light source is shone directly at the IP cameras
- car or traffic lights


Smear (拉光)
Cause:
It is a type of blooming where very strong light source (e.g. sun, car’s
headlights) causes part of the image to be overexposed and the whole
column of pixels becomes overloaded to form vertical white lines.

Solution:
It can be solved by adjusting exposure settings

Scenario:
- when there is glaring sun light


Spot Light Effect
Cause:
When the field of view of the IR LED illuminator is smaller than that of the IP
camera, areas where not covered by the IR LED illuminator appears to be
darker.

Solution:
Use an IR LED illuminator with a wider field of view. However, with a wider
field of view, the IR distance may decrease; or zoom in on the object but the
viewable area becomes smaller.


Q&A


01 lens & sensor technology 20130123

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