MV-D752-28 User’s Manual
REV: 1.0
Page 19/61
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Variation of the sensor characteristics
The LinLog
TM
CMOS image sensors from Photonfocus afford the user the possibility to
adapt the characteristics of the sensor to the requirements of the application.
For normal applications that do not require high contrast, the sensor can be operated in
linear mode. For applications having short exposure times and low illumination intensity,
it is advisable to activate skim mode, in which a non-linear amplification, similar to a
gamma correction, occurs in the pixel so that small signals are amplified significantly
more than large signals (see Variation of the amplification).
In situations involving high intrascene contrast, compression of the upper grey level
region can be achieved with the LinLog
TM
Technology. At low intensities, each pixel
shows a linear response. At high intensities, the response changes to logarithmic
compression. The transition region between linear and logarithmic response can be
smoothly adjusted and is continuously differentiable. This setting is achieved via DAC
channel 4 in the voltage range 0 – 4V (see Appendix E).
For many applications the logarithmic compression of the LinLog
TM
mode is too large. For
this reason the LinLog2
TM
technique was developed by Photonfocus to allow a significantly
more moderate transition between the two response regions. In addition, two further
parameters (lower LinLog value and LinLog2 time) were introduced to control the
transition. At the beginning of the exposure time, high intensities are integrated with the
upper LinLog value, i.e. strong logarithmic compression. After time LinLog2, the lower
LinLog value is activated and lower intensities are integrated with almost linear response.
By varying these three parameters the response can be adjusted to the needs of the
application over a wide range. A detailed description of the LinLog2
TM
technique is
explained in Photonfocus Application note [AS001].
Fig. 9: Response of the various camera modes
0
2
4
6
8
10
12
14
16
18
20
0
5
10
15
20
25
Light intensity
Output signal
LinLog
TM
response
logarithmic
response
linear
response
LinLog transition
point, adjustable