We use known LED sequences to test camera timing. The user will have two or more cameras they wish to test the time synchronization of the exposures via an LED flashing sequence.
Each camera should have a hardware external trigger input that is driven by a stable (long-term and short-term) clock source controlling an ASIC or FPGA outputting a pulse train with period matching the desired frame rate.
Additionally, the cameras should have a "fire" output which is a
hardware output telling the instant when the exposure started. In our
system we pack this into a byte and record this as a .fire file
Octave 4.0+ with octave-fits
and octave-communications packages.
If using Octave from Cygwin see how to install
octave-fits package in Cygwin
or you can use Matlab instead of Octave.
- RunLEDplot: click on LED coordinates, which are saved to *_Coord.h5 files. Plots made to verify clicks (should see square waves with distinct frequencies matching LEDs
- RunledMatcher: given video input, makes plot of simulated LEDs against 1-D pixel vs time brightness. Sim should match video! does NOT use .fire measurements
- Runsimleds: test run of LED simulated square wave (that are used in RunledMatcher)
- RunFireReader: read and plot .fire file recorded from real camera outputs time of exposures corrected for dropped frames
Read and plot a .fire file for manual examination of missed frames, and
estimate of absolute UTC time, where your system sent pps pulses per
second to the camera:
RunFireReader('c:/data/mytest.fire',pps)
Note, because of the extreme zoom-in, you don't see the on-off behavior of the relatively long 1PPS from the Jackson Labs Fury GPSDO.
In the plot above, the camera could not keep up with the requested frame
rate as we do not see a 1:1 correspondence between Ext Trig and
Fire. The width of the pulses don't matter here, it's the fact that
some Ext Trig pulses do not have corresponding Fire pulses, meaning
the camera didn't take a picture without a Fire pulse.
In the plot above, the camera could keep up with the requested frame
rate for the time plotted as we see a 1:1 correspondence between
Ext Trig and Fire.
update RunledMatcher to use the computed time from RunFireRader functions automatically implements correction from RunFireReader
