hdr_instructions - framosimaging/framos-nxp-drivers GitHub Wiki

Application note - setting tuning xml file draft version

Setting HDR modes

Change the mode to dol or clearHDR mode (the last two ones) for imx6* sensor in /opt/imx8-isp/bin/start_isp.sh file and run the script. Then test the stream using the gstreamer

gst-launch-1.0 -v v4l2src device=/dev/video2 ! queue ! waylandsink

v4l2 controls

You can use v4l2 controls to change exposure, very short short exposure and gain, very short gain for DOL2, or exponential gain for ClearHDR like this:

v4l2-ctl -d /dev/v4l-subdev1 -c exponential_gain=30 # 0, 30, 60, 90, 120, 150, 180 for imx676
v4l2-ctl -d /dev/v4l-subdev1 -c exponential_gain=0 # other values 0,1,2,3,4,5 for imx662 and imx678

Setting exposure ratio

To change HDR ratio between exposures change IMX<SENSOR_ID>_Basic_HDR_WIDTHxHEIGHT.xml file to

<hdr enable="true">
            <exposure.ratio>16</exposure.ratio>
            <extension.bit>0</extension.bit>
</hdr>

the second field extension.bit does not have any effect (nxp version 6.6.3). The ISP should now tune the image so the exposure ratio is valid.

Setting auto exposure value and convergence of auto exposure

To set a default value for auto exposure change SetPoint to some value. If you notice that the convergence of auto exposure algorithm is too slow you can increase/decrease convergence of parameters by changing Damp parameters.

      <AEC index="1" type="struct" size="[1 1]">
         <SetPoint index="1" type="double" size="[1 1]">
            [ 80]
         </SetPoint>
         <ClmTolerance index="1" type="double" size="[1 1]">
            [ 20]
         </ClmTolerance>
         <DampOver index="1" type="double" size="[1 1]">
            [ 0.2]
         </DampOver>
         <DampUnder index="1" type="double" size="[1 1]">
            [ 0.3]
         </DampUnder>
         <DampOverVideo index="1" type="double" size="[1 1]">
            [ 0.7]
         </DampOverVideo>
         <DampUnderVideo index="1" type="double" size="[1 1]">
            [ 0.9]
         </DampUnderVideo>
...

Very Short exposure limitation in dol2 mode

Max very short expoure is limited by maximum number of integration lines by NXP (AN13326) which is typically around 1000 us. Check the calculation bellow for you concrete situation.

max_integration_lines = 62
hmax = 1100  # 1H period for selected data rate
line_time = (hmax * 10**6) / (INCK) [us]
max_vs_exposure =  max_integration_lines * line_time

Dol2 image is very noisy and can be used only in overexposed images.

References

  • Application note AN13326 by NXP ISP HDR Modes and Sensor Types
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