Camera technology & fundamentals
Lars Fermum
Chief instructor
STEMMER IMAGING GmbH
www.stemmer-imaging.de
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Specifying the Camera
CAMERA
Purpose and requirements profile of cameras:
High sensitivity
High resolution & frame rate
Excellent image quality, high dynamic range
Low dark current & noise-less signals
Low smear and blooming effects
Reproduction of true colours
Integrated pre-processing functions or assessment functionality
Interfaces for data transfer, digital I/Os etc.
Mechanical details: ideally compact, easy to mount, shock resistant
USE OF THE CORRECT CAMERA
Sensor resolution
CCD/CMOS sensor
Monochrome/colour camera
Monochrome/colour camera
Special wavelengths (UV/IR)
Area scan or line scan camera
Monochrome - visible light
Colour - visible light
Monochrome - infrared light
EFFECT OF RESOLUTION
Zoom from image with 640 x 480 pixels
1:1 representation, 2448 x 2048 pixels
USE OF COLOUR CAMERAS
Colour cameras not only provide brightness information per pixel,
they also provide colour information
Object features with similar levels of brightness could perhaps be detected based on
colour information (=> brightness per colour channel).
MONOCHROME VS. COLOUR
Monochrome sensor
One-chip colour sensor
(interline transfer CCD)
with Bayer Mosaic
BAYER MOSAIC
COLOUR CALCULATION USING THE BAYER MOSAIC:
Although some individual pixels produce R or G or B, RGB information should be
available for each pixel
Typical problems:
Loss of resolution
Loss of brightness
More image data than
monochrome cameras
DISADVANTAGES OF ONE-CHIP COLOUR
CAMERAS
LOSS OF BRIGHTNESS
Both images: identical Sony-CCD without colour filter and with colour filter at 8 ms
exposure time
DISADVANTAGES OF ONE-CHIP COLOUR
CAMERAS
LOSS OF RESOLUTION
Image 1: Colour camera with Bayer mosaic shows colour errors and loss of resolution
Image 2: Monochrome sensor with higher spatial resolution
THREE-CHIP COLOUR CAMERAS
COLOUR SIGNAL ON THREE SENSORS
Full resolution, no colour interpolation
Best colour reproduction and colour
tone differentiation
Note:
Greater structural shape
Specially adapted lenses
Only for PC-based systems and at
the moment only available with up to
2 (genuine) megapixels
LINE SCAN CAMERAS
WHY WORK WITH LINE SCAN CAMERA TECHNOLOGY?
Image recording and configuration are complex, but it is especially good for…
distortion-free image acquisition of round objects such
as cylinders, bottles, bolts & cans
inspection purposes, especially for long components, so
no loss of resolution as is the case with rectangular
surface sensors
interruption-free checking of infinite reeled objects such
as glass, paper, steel, materials, film
image acquisition with high resolution at a lower price
than is the case with surface cameras
vibration/frequency measurement using scan line
camera detectors etc.
LINE SCAN CAMERA SENSORS
General functional principle of line scan cameras & scanning lines
Area scan camera
2D images
X columns * Y rows sensor pixel resolution
Line scan camera
1D "images“
X columns * 1 pixel row resolution
Object movement with line trigger produces an image;
alternatively, the camera unit can scan over the object
Path-based, not time-based image acquisition: Encoder!
LINE SCAN CAMERA APPLICATIONS
Inspecting rolled goods
Film scanning
Flat panel inspection
2D print image checking
Printed circuit boards/solar cells
Fruit/vegetable inspection
SENSOR SIZES OF INDUSTRIAL CAMERAS
Typical for cameras with C-mount adapter:
Special high-resolution area scan cameras, line scan cameras and high-speed cameras
have significantly larger sensors.
CCD SENSORS
CCD: Traditionally, CCD sensors
are preferred in industrial MV.
High light sensitivity
Low noise
Less faulty pixels
Use of micro lenses to increase the fill
factor when in use
Backside illuminated CCDs for
maximum sensitivity
A central A/D digitises all pixel loadings.
Compared with the CMOS, this process produces relatively noiseless images. However,
the camera electronics are more complicated and the image digitisation rate (image rate)
is comparatively low
CMOS SENSORS (1)
CMOS: Hard competition for CCD technology
Less blooming with overexposure
Read-out electronics can be integrated in the sensor
Multi-AOI read-out
Lower costs with high number of units
Lower power consumption
High read-out speed (images/s)
Random access (multi AOI read-out)
More recently, backside illuminated CMOS as well
and in some cases micro lens technology
CMOS technology allows the construction of reasonably priced, compact cameras or very
fast cameras. For welding and traffic applications, value is placed on exposure stability.
The (currently) still higher noise, the (currently) still lower sensitivity and the number of
defective pixels is improving with each new generation of chip.
CMOS SENSORS (2)
CMOS with global shutter
Motion
CMOS with rolling shutter
Motion
Cheaper "rolling shutter" sensors cause distortions with moving images. Global shutter
CMOS sensors require more transistors, are somewhat less sensitive and are more
expensive in terms of manufacturing.
EXAMPLES OF CAMERA ELECTRONICS (2)
Additional camera & pre-processing functions
Partial Scan/ Multi AOI readout
Bayer-to RGB and other colour modes
Blemish pixel correction
Flat field correction (shading removal)
Look-up tables (changing the image dynamics)
Auto shutter / auto gain / auto white balance/ auto iris
Image memory/ buffers
Special trigger modes
E.g. burst mode: 1 trigger => n images
Genuine MV functions: Intelligent camera systems
EMVA 1288 STANDARD
COMPARISON OF CAMERAS
The comparison of cameras from different
manufacturers (with identical sensors) is quite complex.
The EMVA 1288 standard has been developing
methods for standardized evaluation of cameras.
Sensitivity, linearity and noise
Dark current noise
Sensor non-uniformity and defect pixels
Spectral sensitivity
STEMMER IMAGING is testing cameras in detail.
Talk to us about your specific application.
THE KEY TO PERFECT INSPECTIONS
SELECTION OF CAMERA TECHNOLOGY
Using a suitable camera makes image processing
much easier. Images with low noise, high contrasts,
true colours, enough spatial resolution are the key
for robust software inspections.
Please also consider optical possibilities, sometimes
it is easier to change the sensor and lens mount
(and have smaller or bigger sensors/ pixels).
Camera technology is a fast developing market and
there are many different manufacturers, interface
technologies and hardware models. Ask your vision
experts at STEMMER IMAGING.
Thanks a lot for your attention!
STEMMER IMAGING GmbH
Gutenbergstraße 9 – 13
82178 Puchheim, Deutschland
Telefon:
Fax:
+49 89 80902-0
+49 89 80902-116
[email protected]
www.stemmer-imaging.de
Your contact: Lars Fermum