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MT9T111_DG - Rev. B 9/10 EN
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MT9T111: Developer Guide
Flicker Avoidance
Preliminary
If both fd_exec_setperiod and fd_exec_detectperiod flags are set in fd.fd_algo, then the
driver constantly analyzes the image statistics to detect whether the lighting source has
changed from the current frequency to the other frequency. If it detects the change, it
uploads the new flicker period step size to the configuration variable that controls expo-
sure intervals.
The fd.fd_stat_min and fd.fd_stat_max help control the sensitivity of the algorithm to
flickering light in a scene. If the algorithm detects fd.fd_stat_min instances of flickering
in fd.fd_stat_max measurements, then the flicker detection driver responds by changing
the flickering frequency (if different than the existing detected frequency). Altering the
ratio between the two values affects the sensitivity of the algorithm and the time
required to decide whether to change the detected light flicker period.
The detection intervals for the flicker detection driver will be automatically configured
for sensors supported by ROM.
How to Fine-Tune the Anti-Flicker Driver Settings
1. Use Register Wizard to generate the basic anti-flicker settings for the specific timing
conditions, including the following:
VAR8 = 18, 0x44, 0x5C // CAM1_CTX_A_FDPERIOD_50HZ
VAR8 = 18, 0x45, 0x4C // CAM1_CTX_A_FDPERIOD_60HZ
VAR8 = 18, 0xA5, 0x0C // CAM1_FD_SEARCH_F1_50
VAR8 = 18, 0xA6, 0x0E // CAM1_FD_SEARCH_F2_50
VAR8 = 18, 0xA7, 0x0F // CAM1_FD_SEARCH_F1_60
VAR8 = 18, 0xA8, 0x11 // CAM1_FD_SEARCH_F2_60
2. Fine-tune the search window for 50Hz.
If the auto detection function has a high failure rate, decrease the search_f1_50 value
by minus 1, and increase by 1 the search_f2_50 value, to increase the search range.
If +/– 1 is not good enough, increase the range accordingly.
3. Fine-tune the search window for 60Hz in the same way as for 50Hz.
4. Increase the sensitivity of the flicker detection.
stat_min and stat_max help control the sensitivity of the algorithm to flickering light
in a scene. If the algorithm detects stat_min instances of flickering in stat_max mea-
surements, then the flicker detection driver responds by changing the flickering fre-
quency. Altering the ratio between the two values affects the sensitivity of the
algorithm and the time required to decide whether to change the detected light flicker
period. For most applications, the following steps should produce enough sensitivity.
This value can be tuned to suit specific applications.
VAR8 = 8, 0x09, 0x02 // FD_STAT_MIN
VAR8 = 8, 0x0A, 0x05 // FD_STAT_MAX
5. Increase the signal strength sensitivity of the flicker detection.
fd_min_amplitude specifies the signal threshold below which signals are ignored. The
following variable setting should be suitable for most cases. This value can be tuned
to suit specific applications.
VAR8 = 8, 0x0C, 0x01 // FD_MIN_AMPLITUDE
6. Call REFRESH or REFRESH_Mode commands to make the above changes effective.