Teledyne Falcon4 86M User Manual page 74

The PRNU_Auto_Gain algorithm is performed differently for color cameras and makes use of FPGA
capabilities to measure the average of each color over a specified area of interest. The user
interface uses the autoBrightnessROISelector / width / height / OffsetX / OffsetY to enter the
parameters used to determine the region in which the imaging statistics are gathered. The
correction coefficients are calculated over the entire image.
The process of PRNU calculation is
1) Set the camera to use an internal frame rate and integration time close to the final values.
2) Make the camera dark and perform FPN calculation. This is the same for the monochrome
cameras.
3) Add uniform white light so that the most responsive color and least responsive color are
equally above and below 55% of output level with FPN correction on and PRNU correction
off, and with the color and system gains set to unity.
4) Set the region over which the averages are calculated (autoBrightnessROISelector / width /
height / OffsetX / OffsetY)
5) Command PRNU calculation.
The camera's micro code now commands the FPGA to capture the frame average statistic for each
color using a single frame.
The micro then finds:
TargetRed = 1.2*AverageR,
TargetBlue = 1.2*AverageB,
TargetGreenBlue = 1.2*AverageGreenBlue (Green pixels in the blue row)
TargetGreenRed = 1.2*AverageGreenRed (Green pixels in the red row)
The micro code then commands the FPGA to perform PRNU calculation.
Micro calculates the color gains and ensures they are stored with the coefficient set.
GainMaxColor = 1 (assume R for this example, as easier to write the description)
GainGR = AvgR/AvgGR
GainGB = AvgR/AvgGB
GainB = AvgR/AvgB
User Interface Rules
autoBrightnessHeight is a minimum 4 rows, Minimum autoBrightnessWidth = 64 columns
And the autoBrightnessOffsetX is a multiple of 32, autoBrightnessOffsetY is a multiple 2.
The minimum autoBrightnessOffsetY =2+ OffsetY (Avoid the first row of data)
The maximum autoBrightnessHeight is such that the last 2 rows of the output data are omitted.
autoBrightnessHeight < Height -4
The autoBrightnessOffset, width and height are automatically pushed smaller with image ROIs but
don't automatically increase.
If increasing the autoBrightnessOffsetY, it may be that the autoBrightnessHeight needs to first be
reduced before the Y offset can be increased. Remember that the autoBrightnessOffsetY must be a
multiple of 2 and if an odd number is entered then the value is rounded down, if it does not conflict
with the rule autoBrightnessOffsetY> 2+OffsetY. If the requested offsetY can be increased, but not
in its entirety due to the height limitation, then the entered value is automatically adjusted to
achieve the maximum allowed without decreasing the autoBrightnessHeight.
72  Contents
Falcon4 86M Cameras