AE algorithm process
Brightness acquisition: After the image is OB and shading, the image is divided into 64*48 grids to obtain brightness information.
Calculate Target: Use luma target, histogram, bright region, dark region, extreme clolor and other AE information statistics modules to adjust and analyze, and calculate the final target brightness (Target). The basic luminance information and the target luminance are compared and analyzed to determine whether to converge.
Exposure adjustment: If it is determined to converge, enter the exp index through the exposure meter, configure the required exposure time and sersor gain to the sensor, and then do isp gain compensation through gamma, TMC, LTM, GTM, and finally the correct exposure of the photo; if it does not converge If so, loop to the next AE index and continue to acquire brightness until the correct exposure is completed.
How to get the safe target
Calculate the four values of Bright_Low_target, Bright_High_Target, Dark_Low_target and Dark_High_Target, then remove the maximum and minimum values, get the low target and high target,
then compare the reference target luma with the low target and high target, and take the middle The value of is used as safe target.
Finally, compare the safe target obtained in the second step with MinTargetAdjRatio reference target luma and MaxTargetRatio reference target luma, and take the middle value as the final safe target.
Algorithmic flow of LTM
Applies a bilateral filter to generate a nonlinear mask
(applies a bilateral filter to generate a nonlinear mask)
Avoids halo artifacts on the edges Uses an LTM curve set for local
gain adjustment
Adjustment)
Uses a combination of LTM and LCE
to calculate local gain using a combination of LTM and LCE
The role of TMC
Statistics as a mixture of LTM and GTM. The sum of the proportions of LTM and GTM must be equal to 1.
How to calculate index
The Lux index is used to indicate the luminance information of the test condition when the frame luminance exceeds the maximum value exp_index. The index is determined by the following equation:
Therefore, if frame luminance = luminance target of test condition, then lux_index equals exp_index. lux_index helps convey luminance information in frame luminance when exp_index reaches its maximum value.
How did Darkboost gain and adrc gain come about?
Darkboost gain = long target/safe target.
(Take the minimum value of MaxDarkBoostGain and Dark_low_target/safe target, and then compare this minimum value with the value of MaxADRCGain/DRCGain to obtain the minimum value.)
Adrc gain = safe target /short target.
Take the minimum value of bright low target, bright high target and safe target as the short target,
and compare the calculated value of safe target/short target with MaxDRCgain to get the minimum value is the value of adrc gain.
What are the modules that affect the contrast
Gamma LTM GTM TMC
Gamma debugging priority or LTM debugging priority?
Gamma. (gamma affects the global brightness, LTM affects the local brightness, adjust the global first, and then adjust the local)
Frame rate is 240 exposure time
Time=1/frame rate=1/240(s)=4166666(ms)
7250 platform TMC uses 3.0 or 4.0, how to know whether it is 3.0 or 4.0
Qualcomm AE is divided into how many data blocks and how to count
64*48 statistical data blocks, statistics through the center metering mode.
How to debug the Qualcomm exposure meter, what is the main impact
First calculate the vertical blanking time and the exposure time of the first line
FrameLengthLines=Frame_length Line_length is the frame length and line length, the number of pixels in a frame
Vertical Blanking Time=1/maximum frame rate/FrameLengthLines vertical_offset 10^9
First line exposure time=1/maximum frame rate/FrameLengthLines minlinecount 10^9
vertical_offse: vertical compensation
Minlinecount: minimum exposure line
The other lines are exposed in the form of exposure time priority. In order to avoid smearing in dark environments, the last line is exposed in the form of gain priority.
Main impact: AEC exposure meters control image brightness through sensor exposure time and sensor analog gain. Mainly affects brightness and noise
What is the exposure equation?
AV+TV=BV+SV=EV
AV+TV: The supply side of exposure, how much light enters the camera.
BV+SV: The receiving side of the exposure, how much light is reflected on the brightness of the picture.
EV: exposure, aperture size and shutter time combination determine the exposure.
Flash overexposure:
Adjust the ratio flux of the main flash and pre-flash, the larger the flux, the darker the photos taken by the flash.
The video captures human faces, the picture is bright and unstable
1. Adjust the convergence speed of the video to make it slower.
2. Turn off face ae, when a face is detected, the parameters of face ae will not be called, the screen will not change, and the face will be adjusted through tone mapping.
Metering is divided into those two modules?
evtable and ae data statistics
ev table These are the synthesis adjustments of each frame, used for algorithm processing, ae data statistics calculation is the
main parameters of those TMCs that are being adjusted:
TMC is seldom adjusted. One of the recommended parameters is the mixing ratio of GTM and LTM, as well as dark boost ratio, tone target and tone anchors.