Spatial Correction And Bilinear Sensor Design - Dalsa Linea Color CL User Manual

Spatial Correction and Bilinear Sensor Design

The bilinear color camera is based on Teledyne DALSA's bilinear CMOS sensor and designed
such that the first line of this two line sensor has red (R) and blue (B) alternating pixels,
while the second line has all green (G) pixels. The sensor has a 100% fill factor with zero
gap between the two lines, which minimizes any artifact due to spatial correction. The G
channel can be used as a monochrome output.
Top Line
Bottom Line
Note: The interpolation procedure does not work on the first and last pixels. As a result, the
number of effective full color (RGB) pixels is reduced by 2 to 8190 pixels.
There is no spacing between the sensor lines. When the image passes the two lines of
pixels, the red/blue and green components for the same image location are captured at a
different time as dictated by the line spacing. The camera automatically corrects for the line
spacing to ensure that the red/blue and green components of the image pixel are all aligned
when output. However, this is only correct when the object pixel size is square; i.e., the
distance moved by the object for one EXSYNC period is equal to the width of the object
pixel. In some applications it may not be possible to achieve a ‗square' object pixel as fine
adjustment of the lens magnification and/or the distance moved for each EXSYNC period is
not possible. This scenario may be especially apparent when trying to integrate the camera
into an existing system.
When it is not possible to generate a square object pixel, color artifacts will occur in the
scan direction and is particularly noticeable at sharp edge transitions. The size of the edge
artifact is proportional to how far the pixel is from square. To correct for this, the camera
has a feature, Line Spatial Correction (or three letter command ssa), which allows fine
adjustment of the compensation mechanism the camera uses to correct for the line spacing.
The default setting for this feature is 1, which is set for square object pixels. The setting can
be adjusted from 0 to 3 to compensate for rectangular pixels—whether they are too long or
to short.
The following examples of image artifacts show black to white image transitions and the
associated corrected image after applying a specific ssa setting.
10 
Red Blue Red Blue
Pixel 1 Pixel 2 Pixel 3 Pixel 4
Green Green Green Green
Pixel 1 Pixel 2 Pixel 3 Pixel 4
Red Blue Red Blue
Pixel 5 Pixel 6 Pixel 7 Pixel 8
Green Green Green Green
Pixel 5 Pixel 6 Pixel 7 Pixel 8
Red Blue
Pixel Pixel
8191 8192
Green Green
Pixel Pixel
8191 8192
The Linea Color Camera