Graftek Imaging, Inc.
A National Instruments Alliance Member
Providing Complete Solutions For Image
Acquisition and Analysis
INTRODUCTION TO
LINE SCAN CAMERAS
Graftek Imaging, Inc.
What is a Line Scan
Camera?
• A line scan camera is similar to a fax
machine, photocopier or scanner.
• Unlike a photocopier or a scanner, a line
scan camera is able to image very large
and 3D objects.
• Line scan cameras use a one
dimensional array to create a two
dimensional image.
Area Camera Sensor
Line Scan Camera Sensor
• A two dimensional image results from
the movement of the camera or object.
Sensor
• The image is acquired line by line as the
object moves perpendicularly relative to
the sensor.
• Single lines or complete two
dimensional images can be transferred
to the host PC for display, processing or
archiving.
PCB Example Image
Actual Resolution
Original Image = 2545 pixels x 1329 pixels
Benefits of Line Scan
Cameras
• Very high spatial resolution at low cost
• Continuous Image/100% Inspection of
moving objects
• Reduced Distortion
• Even illumination of large areas/objects
Area Cameras
• Area cameras become dramatically more
expensive as their resolution increases.
640 x 480
$700.00
2048 x 2048
$9450.00+
1280 x 1024
$3000.00+
1920 x 1024
$4950.00+
4000 x 2624
$38000.00+
3072 x 2048
$7995.00+
Line Scan Cameras
• By comparison, the price tag to achieve high
resolution with a line scan camera is small.
1024 x 1 $1895.00+
2048 x 1 $1975.00+
4096 x 1 $3725.00+
6144 x 1 $4325.00+
8192 x 1 $4600.00+
Area Cameras
640 x 480 (NTSC)
1000 x 1000
Line Scan Verse Area Scan
640 x 480 (NTSC) = $700.00
1000 x 1000 = $3000.00
4096 x 1 = $3725.00
Line Scan Camera
Applications
• Most line scan camera applications involve
either moving the object or moving the
camera.
• When the object is moving, the line scan
camera behaves like a fax machine. The
object is fed past the sensor.
• When the camera is moving, the line scan
camera is like a photocopier or scanner. The
sensor of the line scan camera sweeps
across the object.
Types of Motion
• Linear Motion
• Rotating Objects
Linear Movement
Original Image 2200 x 11000
Rotating Objects
Original Image 2048 x 19459
System Components
•
•
•
•
•
•
1) Line Scan Camera
2) Lens
3) Frame Grabber
4) Encoder
5) Trigger Source
6) Lighting
Host PC
3
1
2
6
4
5
Motion and Vision
• A line scan camera can
be used to create an
image of a normally
stationary object by
mounting either the
camera or the object on
a linear or rotary stage.
Image Courtesy of
Design and Assembly Concepts, Inc.
Choosing a Line Scan
Camera
• 1) Line Scan Camera
1
Choosing a Line Scan
Camera
• Select Camera Resolution
• Select Camera Line Rate
• Select Camera Output
Camera resolution
• Select the camera’s resolution based on the
application’s requirements.
• Resolution is determined by dividing the
available number of pixels into the field of
view (FOV).
• Line scan cameras are available with the
following resolutions:
512, 1024, 2048, 4096, 6144 and 8192
• A 1024 pixel linear camera viewing a 1m FOV
would have a resolution of approximately
1mm per pixel (0.9765625mm).
Line Rate
• Divide the rate of motion by the per pixel
resolution to determine the minimum line rate,
for example
10 meters per second / 1mm resolution = 10 KHz line rate
• A line rate that is too slow or too fast will
result in geometric distortion of the
object
Elongated
20 KHz
10 KHz
5 KHz
Line Rate
5 KHz
Tech Tip:
10 KHz
Over scanning an
object can accentuate
defects.
20 KHz
Available Line Rates
• As the number of pixels increases, the
maximum line rate of a linear cameras
decreases:
1024 x 1 pixel = 79 kHz
2048 x 1 pixel = 36 kHz
4096 x 1 pixel = 18 kHz
6144 x 1 pixel = 12 kHz
8196 x 1 pixel = 9 kHz
• Note: Maximum exposure time decreases as
the line rate increases.
Choosing a Lens
• 1) Line Scan Camera
• 2) Lens
1
2
Choosing a Lens
• Line scan camera sensors are typically larger
than area camera sensors, resulting in the
need for large format lenses.
• Typical area camera sensors range from
3.6mm x 2.4mm in size to 12.8 mm x 8.8 mm.
• Line scan camera sensors range from 5.12
mm to 57.37 mm wide.
Image of a Line Scan Camera Sensor
Types of Lenses
• Line Scan cameras
with 1024 or fewer
use C-mount or Fmount lenses.
Computar V1213
• Line Scan cameras
with 2048 or more
pixels use F-mount
(photography) or
specialty lenses.
Nikon 60mm f/2.8D AF Micro-Nikkor
Determining Focal Length
• Sensor Size (SS): Multiply Cell Size by the
number of cells (Example: 10mm x 1024 =
10.24mm)
• Field of View (FOV: What is the viewable
area?)
• Focal Length = SS*(Distance/FOV)
Lens
Camera Sensor
Size (SS)
Focal Length (FL)
Field of View
(FOV)
Minimum Focal
Distance (D)
System Components
• 1) Line Scan Camera
• 2) Lens
• 3) Frame Grabber
Host PC
1
2
3
Interfacing Line Scan
Cameras With NI Products
• PCI/PXI-1422 + specific camera cable +
D2504 I/O cable
• PCI-1424 + specific camera cable + D2504
I/O cable + memory upgrade (32 or 64MB)
• PCI-1428 + camera link cable + D6804 I/O
cable
• NI-IMAQ for IEEE-1394 + PCI, PCMCIA, PXI
or CVS-1454 + firewire cable and trigger
cable
Image Acquisition Forms
• Individual lines can be acquired and
sent to the host for processing.
• Individual lines can be built into 2D
images in host PC memory.
• Individual lines can be buffered in frame
grabber memory and sent as complete
images to the host PC for processing.
Encoder
•
•
•
•
1) Line Scan Camera
2) Lens
3) Frame Grabber
4) Encoder
Host PC
1
2
4
3
Acquisition Modes
• Free running- the camera acquires lines
at a predetermined rate, if the rate of
movement changes the image will
elongate or contract proportionally.
• Encoded- the line rate of the camera is
determined by an encoder. A single line
is generated each time the camera
receives a pulse from an encoder.
Free Running
• Objects contract and elongate as the
rate of motion changes.
Encoded
• The image’s geometry remains constant
as the rate of motion changes.
Trigger
•
•
•
•
•
1) Line Scan Camera
2) Lens
3) Frame Grabber
4) Encoder
5) Trigger Source
4
Host PC
1
2
5
3
Triggered Acquisition
• Like area scan cameras, the start of each
image can be triggered via an external TTL
signal.
• Line scan cameras can also take advantage
of Variable Height Acquisition. Here, the
beginning and end of the image is determined
by a TTL signal, varying the size of the image
to match changes in the length of the object.
Continuous Image
Acquisition
• When the inspection is of a continuous object
(for example a moving web or cable), it is not
necessary to provide a trigger signal.
• The image is transferred to the host for
processing based on frame grabber and
application requirements.
Triggered Image Acquisition
• When the inspection is of discreet
objects, it is necessary to synchronize
the start of image acquisition with the
arrival of the component/object.
Images Acquired at Regular Intervals
5
Triggered Acquisition
Lighting
•
•
•
•
•
•
1) Line Scan Camera
2) Lens
3) Frame Grabber
4) Encoder
5) Trigger Source
6) Lighting
Host PC
3
1
2
6
4
5
Light Guides
• The most common form of illumination
for line scan cameras is the line light.
Line lights are available off the shelf in
widths ranging from 1 inch to 40 inches.
6” Line Light
40” Line Light
Light Guides
• A line lights can be used as a bright
field, diffuse on axis, dark field or
backlight.
• Pairs of line lights can be used to
achieve different lighting geometries or
to increase the amount of available
light.
• Custom line lights are available with
multiple light inputs for increased light
output.
Line Lights
• A typical line light system consists of
two to four parts.
Cylindrical or
Apertured Lens
Light Source
Line Light
And/Or
Polarizer
Bright Field
• General (Single or Dual Line Lights) Non-Critical Applications
Non Polarized
Polarized
Direct On Axis
• Direct on Axis - Flat, Specular
Surfaces
Dark Field
• Dark-Field - Flat, Diffuse Surfaces
Bright Field
Dark Field
Back Light
• Back-Light - Contour Analysis, Clear
Substances
Lighting
• For even illumination of the object, the
light guide should be wider than the
object.
Contacting Graftek Imaging,
Inc.
• Phone: (512) 416-1099
• Email: eastlund@graftek.com
• URL: www.graftek.com