Sony Pregius Global Shutter CMOS Imaging Performance - What's inside: Sony Pregius technology What is the EMVA1288 standard? EMVA1288 ...
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Point Grey White Paper Series
Point Grey White Paper Series
Sony Pregius Global Shutter
CMOS Imaging Performance
What’s inside:
• Sony Pregius technology
• What is the EMVA1288 standard?
• EMVA1288 measurement explained
• Apparent sensitivity
Point Grey White Paper Series
In 2014 Sony introduced a new global shutter (GS) CMOS
imaging device, featuring a technology called PregiusTM, that
redefines the GS CMOS imaging category and provides the
best of both worlds with fast frame rate and CCD-like imaging
performance. Sony’s first Pregius sensor, the IMX174 raises the bar on CMOS imaging
quality and in some applications is a viable alternative to CCD sensors. This white paper
will explore IMX174’s imaging performance through the use of EMVA1288
measurement comparing the IMX174 against a popular CCD, the ICX274.
What is the EMVA1288 standard?
Before the IMX174’s imaging performance is discussed, it’s
important to understand what EMVA1288 is. The EMVA1288
standard1 was put together by the European Machine Vision
Association to develop a unified and meaningful method of
measuring a camera’s imaging performance. It is different
from consumer cameras which are often measured in lux.
Lux is a measurement of intensity as perceived by the human eye. It is modelled using
the response of the human eye and may not be representative of how a machine would
recognize an image. In addition, the lux value of a camera represents the minimum
illumination the camera requires to capture an acceptable image. Not only is the
definition of an “acceptable image” subjective, it doesn’t provide any information on
image noise.
Instead of lux, the EMVA1288 uses metrics such as read noise and full well depth to
describe a camera’s performance. Each measurement is characterized using a
standardized method defined by the EMVA1288 standard, providing an objective
performance comparison between different cameras from different vendors. For this
whitepaper, we will compare the 2.3 megapixel CMOS IMX174 with another 2
megapixel CCD, the ICX274.
Sensor Specification Sony ICX274 Sony IMX174
Sensor Technology CCD CMOS
Optical Format 1/1.8” 1/1.2”
Pixel Size 4.4 μm 5.86 μm
Resolution 1624x1224 (2.0 MP) 1920x1200 (2.3 MP)
1
http://www.emva.org/cms/upload/Standards/Stadard_1288/EMVA1288-3.0.pdf
© 2014 Point Grey Research Inc 9/29/2014
Point Grey White Paper Series
Quantum Efficiency
EMVA1288 Sony ICX274 Sony IMX174
Quantum Efficiency @ 525nm 59% 76 %
Quantum efficiency (QE) is a measurement of the sensor’s ability to convert photons to
electrons. A sensor with higher quantum efficiency is better for low light applications
due to better conversion efficiency. The quantum efficiency for a given sensor is
influenced by its photodiode design and will vary across the light spectrum.
When comparing the two QE curve in the above graph, the IMX174 has equal or better
quantum efficiency than the ICX274 across most of the spectrum. At a wavelength of
525nm, the IMX174 is 17% more efficient at converting photons to electrons. But what
does this mean in terms of real world performance?
If two sensors had the same pixel size and saturation capacity, and sensor A has 17%
higher QE at a particular wavelength than sensor B, then sensor A is more sensitive and
will require 17% less light to achieve the same image intensity. This means less
illumination is required to achieve the same result. However, since IMX174 and ICX274
have different pixel size and saturation capacity, the same conclusion cannot be drawn
based on the quantum efficiency alone.
© 2014 Point Grey Research Inc 9/29/2014Point Grey White Paper Series
Temporal Dark Noise
EMVA1288 Sony ICX274 Sony IMX174
- -
Temporal Dark Noise (Read Noise) 8.35 e 6.83 e
Temporal dark noise (read noise) is noise generated by the sensor and camera circuitry
and is influenced by the electrical design. Temporal dark noise can be amplified when
the camera gain is increased, degrading image quality as a result. A low temporal dark
noise allows for more signal gain without sacrificing image quality. Historically, CCD
sensors have much lower temporal dark noise when compared to CMOS sensors.
However, IMX174’s Pregius design features more accurate signal measurement
technology (see Sony Pregius Technology section below), enabling the sensor to achieve
a low temporal dark noise of 6.83 e-.
Saturation Capacity & Dynamic Range
EMVA1288 Sony ICX274 Sony IMX174
- -
Saturation Capacity 7969 e 32513 e
Dynamic Range 59.09 dB 72.94 dB
Sensors with a larger light sensitive area (larger pixel size) will be exposed to more
incoming photons and generate more charge, leading to a higher saturation capacity.
The IMX174 sensor has a pixel size that is 1.75 times larger than the ICX274; however, it
has a saturation capacity that is 4 times larger due to the improved pixel design. But
what does this mean in terms of imaging? It means an analog to digital converter will be
able to convert the electrons in to more grey levels, resulting in a higher dynamic range
in the captured image.
Applications where it’s important to recognize details
in both dark and bright areas such as license plate
recognition will benefit greatly from the higher
dynamic range. Bright vehicle headlights will typically
drive the camera to reduce exposure time, resulting
in the license plate being too dark to be recognized.
A high dynamic range camera will be able to produce
enough detail in the darker areas for the license plate to be recognized.
© 2014 Point Grey Research Inc 9/29/2014Point Grey White Paper Series
Apparent Sensitivity
A common misconception is that a higher sensitivity camera should yield a brighter
image for the same exposure time when compared to a low sensitivity camera. This
method of comparison ignores the difference in saturation capacity and temporal dark
noise between two cameras. To understand how this works, we can use a bucket
analogy to explain what happens when a pixel is exposed to incoming light.
Sensor pixels can be viewed as buckets catching rainfall (photons). A larger bucket will
have a larger volume (saturation capacity). The volume of rain collected will be
proportional to the image intensity. An empty bucket represents a black image while a
full bucket represents a white image. If the rate of rainfall is constant (constant
exposure and illumination), a small bucket will fill up much quicker than a big bucket,
resulting in higher image intensity.
When evaluating camera sensitivity based on image brightness, the camera with smaller
saturation capacity will typically appear brighter when compared to a camera with
larger saturation capacity. This ignores the benefit that large saturation capacity brings,
which is higher dynamic range. For applications that are only detecting whether an
object is present and do not require a high dynamic range image, evaluating apparent
sensitivity alone is a relevant way to compare. To improve apparent sensitivity, cameras
with low temporal dark noise are excellent choices, enabling the use of camera gain to
increase image brightness without sacrificing image quality.
© 2014 Point Grey Research Inc 9/29/2014Point Grey White Paper Series
Sony Pregius Technology
A technique called Correlated Double Sampling (CDS) is a common method used by CCD
and CMOS cameras to reduce temporal dark noise. In CMOS sensors, this can be done
on both the analog and digital level to maximize noise reduction. Sony’s Exmor line of
rolling shutter CMOS sensors performs both analog and digital CDS. With global shutter
CMOS sensors, an additional storage element next to the pixel is required in order to
support analog CDS. However, this additional storage element may reduce the surface
area of the photodiode, reducing saturation capacity.
Sony has overcome this challenge by introducing a new global shutter CMOS pixel
technology called Pregius, first featured in the Sony IMX174 CMOS sensor. The
technology integrates an analog memory storage element as part of the pixel design.
After integration, charges are shifted from the photodiode to the analog memory and
CDS is applied, reducing temporal dark noise. Sony has leveraged their expertise in CCD
pixel design to ensure the additional analog memory does not reduce the pixel’s
saturation capacity.
© 2014 Point Grey Research Inc 9/29/2014Point Grey White Paper Series
As demonstrated by the Sony IMX174, the Pregius technology delivers impressive
imaging performance, exceeding other global shutter CMOS sensor in its category. A
comparison with other global shutter CMOS sensors can be seen below.
Sensor IMX1742 CMV40003 VITA13004 EV76C5605
Manufacturer Sony CMOSIS On Semi e2v
Resolution 1920 x 1200 2048 x 2048 1280 x 1024 1280 x 1024
Pixel Size 5.86 µm 5.5 µm 4.8 µm 5.3 µm
- - - -
Temporal Dark Noise 7e 16 e 26 e 25 e
- - - -
Saturation Capacity 32,691 e 7,620 e 10,226 e 7,507 e
Dynamic Range 73 dB 52 dB 51 dB 49 dB
Quantum Efficiency @ 525 nm 77 % 53 % 61 % 61 %
The EMVA1288 standard not only provides users an objective way for customers to
compare different sensors and cameras, it also helps them evaluate new sensor
technology such as Sony Pregius and understand how the technology can help them.
In summary:
Low temporal dark noise allows for more signal gain without compromising on
image quality.
Large saturation capacity and high dynamic range is great for dynamic scenes
with different lighting conditions.
Higher quantum efficiency means less illumination is required because of more
efficient photon to electron conversion.
Understanding what each measurement represents will help with camera selection and
proper evaluation of camera and sensor performance.
The Sony IMX174 is shipping with Point Grey’s high performance Grasshopper3 camera
platform, available in both GigE and USB 3.0. For more product information or
EMVA1288 imaging performance measurements, please visit www.ptgrey.com.
2
http://www.ptgrey.com/support/downloads/downloads_admin/Dlds/GS3-PGE_ImagingPerformance.pdf
3
http://www.ptgrey.com/support/downloads/downloads_admin/Dlds/GS3-U3_ImagingPerformance.pdf
4
http://www.ptgrey.com/support/downloads/downloads_admin/Dlds/FL3-U3_ImagingPerformance.pdf
5
http://www.ptgrey.com/support/downloads/downloads_admin/Dlds/BFLY-PGE_ImagingPerformance.pdf
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