PYTHON25K Datasheet, PDF (24/87 Pages) ON Semiconductor – PYTHON 25K/16K/12K/10K Global Shutter CMOS Image Sensors

NOIP1SN025KA, NOIP1SN016KA, NOIP1SN012KA, NOIP1SN010KA
Table 18. CONFIGURABLE PARAMETERS FOR BLACK LEVEL ALGORITHM
Group
Addresses
Description
Black Line Generation
197[7:0]
black_lines
This register configures the number of black lines that are generated at the start of a
frame. At least one black line must be generated. The maximum number is 255.
Note: When the automatic black-level calibration algorithm is enabled, make sure that this
register is configured properly to produce sufficient black pixels for the black-level filtering.
The number of black pixels generated per line is dependent on the operation mode and
window configurations:
Each black line contains 80 kernels.
197[12:8]
gate_first_line
A number of black lines are blanked out when a value different from 0 is configured.
These blanked out lines are not used for black calibration. It is recommended to enable
this functionality, because the first line can have a different behavior caused by boundary
effects. When enabling, the number of black lines must be set to at least two in order to
have valid black samples for the calibration algorithm.
Black Value Filtering
129[0]
auto_blackcal_enable
Internal black-level calibration functionality is enabled when set to ‘1’. Required black level
offset compensation is calculated on the black samples and applied to all image pixels.
When set to ‘0’, the automatic black-level calibration functionality is disabled. It is possible
to apply an offset compensation to the image pixels, which is defined by the registers
129[10:1].
Note: Black sample pixels are not compensated; the raw data is sent out to provide ex-
ternal statistics and, optionally, calibrations.
129[9:1]
blackcal_offset
Black calibration offset that is added or subtracted to each regular pixel value when au-
to_blackcal_enable is set to ‘0’. The sign of the offset is determined by register 129[10]
(blackcal_offset_dec).
Note: All channels use the same offset compensation when automatic black calibration is
disabled.
The calculated black calibration factors are frozen when this register is set to 0x1FF
(all−‘1’) in auto calibration mode. Any value different from 0x1FF re−enables the black
calibration algorithm. This freezing option can be used to prevent eventual frame to frame
jitter on the black level as the correction factors are recalculated every frame. It is recom-
mended to enable the black calibration regularly to compensate for temperature changes.
129[10]
blackcal_offset_dec
Sign of blackcal_offset. If set to ‘0’, the black calibration offset is added to each pixel. If set
to ‘1’, the black calibration offset is subtracted from each pixel.
This register is not used when auto_blackcal_enable is set to ‘1’.
128[10:8]
black_samples
The black samples are low-pass filtered before being used for black level calculation. The
more samples are taken into account, the more accurate the calibration, but more samples
require more black lines, which in turn affects the frame rate.
The effective number of samples taken into account for filtering is 2^{black_samples}.
Note: An error is reported by the device if more samples than available are requested
(refer to registers 136 to 139).
Black Level Filtering Monitoring
136
blackcal_error0
An error is reported by the device if there are requests for more samples than are available
137
blackcal_error1
(each bit corresponding to one data path). The black level is not compensated correctly if
138
blackcal_error2
one of the channels indicates an error. There are three possible methods to overcome this
situation and to perform a correct offset compensation:
139
blackcal_error3
• Increase the number of black lines such that enough samples are generated at the
cost of increasing frame time (refer to register 197).
• Relax the black calibration filtering at the cost of less accurate black level determina-
tion (refer to register 128).
• Disable automatic black level calibration and provide the offset via SPI register upload.
Note that the black level can drift in function of the temperature. It is thus recommended
to perform the offset calibration periodically to avoid this drift.
NOTE: The maximum number of samples taken into account for black level statistics is half the number of kernels.
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