Cheetah KAC Camera User Manual | Camera Link (CLF) Interface
October 1, 2019
Page
93
of
135
Rev 7.2
Figure 53: Color subsampling with N = 2 and M = 4.
5.7 Exposure Control
5.7.1 Internal Exposure Control, Electronic Shutter
In rolling shutter mode, each line is reset (cleared of signal) sequentially (one after
another). The delay between the time that a line is reset and the time when this line is
read out is the exposure time. While rolling shutter mode offers superior noise
performance (and thus better sensitivity) as compared to global shutter mode, in rolling
shutter mode each line of the image is captured at a slightly different time and this can
introduce image artifacts when the camera or the object is moving.
In global shutter mode, all pixels in the array are reset at the same time, allowed to collect
signal during the exposure time and then readout sequentially. In this way, all pixels
capture the image during the same time period reducing any image artifacts due to
motion within the scene or the camera.
In free-running mode for both global and rolling shutter modes, the exposure time
overlaps the camera readout and is positioned to occur at the end of the frame readout.
The internal exposure control timer controls the exposure and is organized into two
counters: a line counter and a partial-line (sub-line) counter. In free-running mode, frames
are readout one after another so the maximum exposure time is equal to the frame time.
With no frame period control (Fixed Frame Period disabled), there are 1146 lines per
frame in the C2880 camera (2292 rows) and 1568 lines per frame in the C4080 camera
(3136 rows). Increasing the frame period using the Fixed Frame Period control, adds
additional lines (vertical blanking) to the frame readout thereby increasing the frame
period and increasing the maximum exposure time.
The exposure time can be computed by first converting the contents of the Integration
Lines counter and Integration Clocks (partial line) counter to time using the following
Frame A exposure time equation. (Frame B is the same, save the register addresses have
different values)
1)
Exposure Time = (Integration Lines Counter [e.g., Reg 0728] x Line Time [e.g., Reg
0710]) + (Integration Clocks (Partial Line) Counter [e.g., Reg 072C] x 6.25 nS )
