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Color Line Scan Cameras

Triple Line and Dual Line RGB Sensor Technology

Color line scan cameras are able to scan the surfaces of moving objects in color. Typical applications are:

  • Surface inspection of wood, ores and minerals
  • Scanning of books and documents
  • Quality control of printing
  • Sorting colored objects, in bulk

The sensors use red, green and blue (RGB) color-sensitive pixels. With up to 7,600 pixels per color, very high optical resolutions are possible. A document in A3 size can be scanned at up to 650 dpi or 39 μm per pixel. For truecolor imaging, hardware and software functions for white balance, black level correction and color correction are available. Color calibration using an IT8-target is also possible.

Image Acquisition

Scanning process: triple line sensor
Scanning process: triple line sensor

The acquisition of a color image is achieved by performing a scanning movement of the object or the camera, respectively. The precise synchronization of transport speed and image acquisition ensures the correct aspect ratio and reproducible resolution of the image.

For a given object velocity v0 and field of view FOV, the line frequency fL can be calculated from the pixel width w and length of the sensor S using:

{!{!{f_L = \frac {v_0 \cdot S} {w \cdot FOV}}!}!}

Compliance with conditions of the formula F1 (above) is also a prerequisite for accurate color mixing of the RGB colors in the image. Triple line sensors, especially, with their large line spacing produce color convergence errors when F1 is not applicable.

Triple Line Sensors

Triple line sensors
Pixel order and line signal of
the SK22500CNEC-XC Sensor

Line scan cameras are designated according to the number of line sensors as triple line, dual line or single line sensors. Schäfter+Kirchhoff offers most camera models with triple line sensors.

Triple line sensors have three separate rows of sensors for the primary colors red (R), green (G) and blue (B). The positions of the R, G and B pixels are defined precisely and triple line sensors exhibit particularly high resolutions. The distance between the line sensors (line spacing) is generally 1, 2, 8 or 9-times the pixel height (h). This spatial distance in the translational direction is automatically corrected during production of the image. For exact color mixing, line synchronous image acquisition according to formular F1 and the direction of transport are particularly important. The color information of a picture with a delay line, Ld, of cycles is incomplete. The line delay Ld is twice the line spacing LS divided by the pixel height h, with both usually measured in microns:

Ld = 2 LS / h

Applications in which the transport velocity is not exactly known, such as when imaging bulk products, during free-fall or a photo-finish in a race, should use color line scan cameras with a low line spacing. This has the added advantage that the color convergence errors from the not fully-synchronous signals are smaller and may be neglected.

Dual Line Sensors

The Dual Line Sensor has two directly adjoining lines. The first line contains 1,024 each of alternating red and blue pixels. The second line contains 2,048 green pixels. By caching the red-blue line, the pixels are correctly positioned inside the camera.

Advantages: The color information is included in a single line scan. Minimal color convergence errors with asynchronously moving objects (free-fall or photo-finish camera).

dual line pixel arrangement
Pixel arrangement for a dual line sensor

Types

No
Line Scan Camera
Order code
Pixel
Pixel size [µm]
Active length [mm]
Max.
Pixel freq.
[MHz]
Max.
Line freq.
[kHz]
Anti- Bloom
Integr. cntrl
Shading Correc­tion
Thresh­old Mode
Interface
Dynam. range
Video Signal
1
2096 x 3
14 x 14
29.3
60
9.3
 
X
X
 
GigE
1:2500
8/12 Bit
2
2700 x 3
8 x 8
21.6
24
2.9
 
X
X
 
GigE
1:2000
8/12 Bit
3
3648 x 3
8 x 8
29.2
24
2.1
 
X
X
 
GigE
1:2000
8/12 Bit
4
4080 x 3
10 x 10
40.8
90
7.2
X
X
X
 
GigE
1:2500
8/12 Bit
5
5360 x 3
8 x 8
42.9
24
1.5
 
X
X
 
GigE
1:2000
8/12 Bit
6
7456 x 3
4.7 x 4.7
35.0
120
5.1
 
 
X
 
GigE
1:1000
3*8 Bit
7
7600 x 3
9.3 x 9.3
70.9
120
4.9
 
 
X
 
GigE
1:1000
3*8 Bit
8
2096 x 3
14 x 14
29.3
60
9.3
 
X
X
 
GigE Vision
1:2500
3*8 Bit
9
2700 x 3
8 x 8
21.6
24
2.9
 
X
X
 
GigE Vision
1:2000
8/12 Bit
10
3648 x 3
8 x 8
29.2
24
2.1
 
X
X
 
GigE Vision
1:2000
8/12 Bit
11
4080 x 3
10 x 10
40.8
60
7.2
X
X
X
 
GigE Vision
1:2500
3*8 Bit
12
5360 x 3
8 x 8
42.9
24
1.5
 
X
X
 
GigE Vision
1:2000
8/12 Bit
13
7456 x 3
4.7 x 4.7
35.0
120
5.1
 
 
X
 
GigE Vision
1:1000
3*8 Bit
14
7600 x 3
9.3 x 9.3
70.9
120
4.9
 
 
X
 
GigE Vision
1:1000
3*8 Bit
15
2096 x 3
14 x 14
29.3
60
9.3
 
X
X
 
USB 3.0
1:2500
8/12 Bit
16
2700 x 3
8 x 8
21.6
24
2.9
 
X
X
 
USB 3.0
1:2000
8/12 Bit
17
3648 x 3
8 x 8
29.2
24
2.1
 
X
X
 
USB 3.0
1:2000
8/12 Bit
18
4080 x 3
10 x 10
40.8
90
7.2
X
X
X
 
USB 3.0
1:2500
8/12 Bit
19
5360 x 3
8 x 8
42.9
24
1.5
 
X
X
 
USB 3.0
1:2000
8/12 Bit
20
7456 x 3
4.7 x 4.7
35.0
150
6.4
 
 
X
 
USB 3.0
1:1000
3*8 Bit
21
7600 x 3
9.3 x 9.3
70.9
150
6.2
 
 
X
 
USB 3.0
1:1000
3*8 Bit
22
2096 x 3
14 x 14
29.3
60
9.3
 
X
X
 
Camera Link
1:2500
8/12 Bit
23
4080 x 3
10 x 10
40.8
60
4.8
X
X
X
 
Camera Link
1:2500
8/12 Bit
24
7456 x 3
4.7 x 4.7
35.0
150
6.4
 
 
X
 
Camera Link
1:1000
3*8 Bit
25
7600 x 3
9.3 x 9.3
70.9
150
6.2
 
 
X
 
Camera Link
1:1000
3*8 Bit
26
2096 x 3
14 x 14
29.3
60
9.3
 
X
 
 
LVDS
1:2500
8/12 Bit
27
4080 x 3
10 x 10
40.8
60
4.8
X
X
 
 
LVDS
1:2500
8 Bit

Schäfter + Kirchhoff GmbH - specialists for optical sensors and measurement technology
Kieler Str. 212, D-22525 Hamburg, Tel. +49(0)40 85 39 97-0, Fax +49(0)40 85 39 97-79
E-Mail info~at~SuKHamburg.de