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11-2014 E

Pictures with color fidelity require a color calibration of the line camera.

This process requires a scanner system with a translation unit and the

scanner software

SKan-G from Schäfter+Kirchhoff (Figure 7).

The Dual Line Sensor has two directly adjoining lines. The first line

contains 1024 each of alternating red and blue pixels. The second line

contains 2048 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).

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:

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.

Line buffer Line signal

...2048

B1 R2 B2R1

...2048

... 2x 2048

Dual line sensor

Figure 5 Pixel arrangement for a dual line sensor

2D image acquisition data, using a dual line color sensor signal with one line

of 2048 green pixels and a second line with 1024 each of alternating red and

blue pixels, can be produced by either:

using all green pixels once, and the red and blue pixels twice each, so

that 2048 image points per line are generated, or

combining the red and blue pixel data with the mean of two adjacent green

pixels so that 1024 image points per line are generated, which results in

a lower resolution image than above.

G1 G2 G3 G4

... 2x 2048

... 4096

1 2 3 4

B1 R2 B2R1

R2 B2

R2 B2G1 B1R1 G2 B1R1

G1 G2 G3 G4

... 2x 2048

... 20481 2

B1 R2 B2R1

B1R1 G12 B2R2 G34

Higher resolution

Line signal

Lower resolution

Line signal

RGB data

Figure 6. Alternative processing of the line signal for RGB imaging:

Dual Line Camera SK4096DJRC

Dual Line Sensor

Color management of pictures with color fidelity

Image acquisition with Dual Line Sensors

Figure 7

Line camera SK22800GJRC-XC

Modular Focus Adapter FA26-S55

Lens inspec.x L5.6/105 b-0.33

LED Linelight MTD LED CP 300

Translation unit SK8030-21-J

Triple Line Sensors

Ld = 2 LS / h

Color acquisition with Triple Line Sensors

The color line scan

camera delivers the red

(R), green (G) and blue

(B) signals sequentially

in a single line signal.

Asynchronous trans-

port during image

acquisition results

in inappropriate pixel

designations and color

convergence aberra-

tion (Figure 2).

...2096 Pixel

... 3x 2096

14 μm

= 112 μm

8x 14 μm

112 μm

Line signal

line 1

Line 9

Line 17

RGB data

Figure 3 Pixel arrangement:

Triple Line

Camera

SK6288GKOC-L

... 20961 2

Figure 4 Processing of a line

signal for RGB image:

Triple Line

Camera

SK6288GKOC-L

Figure 2. Monochrome font pattern

Line synchronous object transport

Asynchronous transport of the object

causes color convergence aberration

1 2 ... 15 16 17 18 19 20 21 22 23 24

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