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# Copyright 2014 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import its.image
import its.caps
import its.device
import its.objects
import os.path
import pylab
import matplotlib
import matplotlib.pyplot
def main():
"""Measure jitter in camera timestamps.
"""
NAME = os.path.basename(__file__).split(".")[0]
# Pass/fail thresholds
MIN_AVG_FRAME_DELTA = 30 # at least 30ms delta between frames
MAX_VAR_FRAME_DELTA = 0.01 # variance of frame deltas
MAX_FRAME_DELTA_JITTER = 0.3 # max ms gap from the average frame delta
with its.device.ItsSession() as cam:
props = cam.get_camera_properties()
if not its.caps.manual_sensor(props):
print "Test skipped"
return
req, fmt = its.objects.get_fastest_manual_capture_settings(props)
caps = cam.do_capture([req]*50, [fmt])
# Print out the millisecond delta between the start of each exposure
tstamps = [c['metadata']['android.sensor.timestamp'] for c in caps]
deltas = [tstamps[i]-tstamps[i-1] for i in range(1,len(tstamps))]
deltas_ms = [d/1000000.0 for d in deltas]
avg = sum(deltas_ms) / len(deltas_ms)
var = sum([d*d for d in deltas_ms]) / len(deltas_ms) - avg * avg
range0 = min(deltas_ms) - avg
range1 = max(deltas_ms) - avg
print "Average:", avg
print "Variance:", var
print "Jitter range:", range0, "to", range1
# Draw a plot.
pylab.plot(range(len(deltas_ms)), deltas_ms)
matplotlib.pyplot.savefig("%s_deltas.png" % (NAME))
# Test for pass/fail.
assert(avg > MIN_AVG_FRAME_DELTA)
assert(var < MAX_VAR_FRAME_DELTA)
assert(abs(range0) < MAX_FRAME_DELTA_JITTER)
assert(abs(range1) < MAX_FRAME_DELTA_JITTER)
if __name__ == '__main__':
main()
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