Cheetah KAC Camera User Manual | Camera Link (CLF) Interface
October 1, 2019
Page
109
of
135
Rev 7.2
1.
Set the overall camera exposure time so areas in the darkest regions of the
image have contrast and bright areas are overexposed.
2.
Set Texp - E1 to 10% of the overall exposure time and set Texp - E2 to 1% of the
overall exposure time.
3.
Set P1 to 40%, P2 to 70%, and P3 to 100%.
Compressing the bright areas of the image into the camera’s output range will make wide
dynamic range images look flat and dark. The histogram of the output is useful for seeing
the impact of changes to P1, P2, and P3 settings. The LUT function can stretch the image
and increase the image brightness, if needed, keeping in mind that data is not linear and is
partitioned into different exposure ranges.
5.11.4 WDR at Maximum Frame Rates (image
artifact prevention)
To provide the highest frame rates, the exposure time and read-out time overlap; this
means that while Frame 1 is being read out, Frame 2 is being exposed. The exposure time
for Frame 2 is always positioned at the end of the Frame 1 and any additional WDR
exposures (E1, E2, and E3) are positioned at the end of the overall exposure time.
When the application demands maximum frame rate, the exposure time of Frame 2
overlaps with the readout of Frame 1 (for lower frame rate applications, the exposure for
Frame 2 will occur after Frame 1 is read out (non-overlapping)). An image artifact (a faint
horizontal line) might appear at the beginning of the WDR (E1, E2, and E3) exposures if
the WDR exposures for Frame 2 overlap with the Frame 1 read-out time. At maximum
frame rate, these artifacts typically occur very near the bottom of the image.
For example, suppose the camera is providing a system-constrained maximum frame rate
of 50 fps (20,000 microsecond frame time). Also, suppose the exposure time (Texp) is
5,000 microseconds and two additional WDR exposures (E1 and E2) are used. E1 is set to
4,000 microseconds (a WDR exposure of 1,000 microseconds) and E2 is set to 4,900
microseconds (a 2
nd
WDR exposure of 100 microseconds). Assume a full 4000 x 3000
resolution image is read out from the C4080 camera and Frame 1 begins reading out at
time equals 0 seconds. In this example, the exposure for Frame 2 begins 15,000
microseconds after Frame 1 readout begins (5,000 microseconds before the end of the
Frame 1 read-out time) and the first WDR exposure (E1) begins 1,000 microseconds
before the end of Frame 1 readout. Finally, the 2
nd
WDR exposure (E2) begins 100
microseconds before the end of the Frame 1 readout. In this example, two-line artifacts
might appear. These artifacts will be located where they occurred with respect to the
readout of Frame 1 in time. For the E1 exposure, the artifact may be seen at image line
150 (1000 microseconds before the end of the frame readout) and, for the E2 exposure,
an artifact at line 15 (100 microseconds before the end of the Frame 1 readout) might
appear. If the E1 and E2 exposures do not overlap with the readout of Frame 1, no
artifacts will appear.
To eliminate these artifacts when trying to achieve maximum frame rates:
•
Enable the Fixed Frame Period control to increase the frame time slightly so the
WDR exposures occur after the frame readout ends. For example, if the
minimum frame time is 20ms (50 fps) and the longest WDR exposure desired is
