1 # Copyright 2014 The Android Open Source Project 2 # 3 # Licensed under the Apache License, Version 2.0 (the "License"); 4 # you may not use this file except in compliance with the License. 5 # You may obtain a copy of the License at 6 # 7 # http://www.apache.org/licenses/LICENSE-2.0 8 # 9 # Unless required by applicable law or agreed to in writing, software 10 # distributed under the License is distributed on an "AS IS" BASIS, 11 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 # See the License for the specific language governing permissions and 13 # limitations under the License. 14 15 import its.image 16 import its.caps 17 import its.device 18 import its.objects 19 import os.path 20 from matplotlib import pylab 21 import matplotlib 22 import matplotlib.pyplot 23 24 def main(): 25 """Measure jitter in camera timestamps. 26 """ 27 NAME = os.path.basename(__file__).split(".")[0] 28 29 # Pass/fail thresholds 30 MIN_AVG_FRAME_DELTA = 30 # at least 30ms delta between frames 31 MAX_VAR_FRAME_DELTA = 0.01 # variance of frame deltas 32 MAX_FRAME_DELTA_JITTER = 0.3 # max ms gap from the average frame delta 33 34 with its.device.ItsSession() as cam: 35 props = cam.get_camera_properties() 36 its.caps.skip_unless(its.caps.manual_sensor(props) and 37 its.caps.sensor_fusion(props)) 38 39 req, fmt = its.objects.get_fastest_manual_capture_settings(props) 40 caps = cam.do_capture([req]*50, [fmt]) 41 42 # Print out the millisecond delta between the start of each exposure 43 tstamps = [c['metadata']['android.sensor.timestamp'] for c in caps] 44 deltas = [tstamps[i]-tstamps[i-1] for i in range(1,len(tstamps))] 45 deltas_ms = [d/1000000.0 for d in deltas] 46 avg = sum(deltas_ms) / len(deltas_ms) 47 var = sum([d*d for d in deltas_ms]) / len(deltas_ms) - avg * avg 48 range0 = min(deltas_ms) - avg 49 range1 = max(deltas_ms) - avg 50 print "Average:", avg 51 print "Variance:", var 52 print "Jitter range:", range0, "to", range1 53 54 # Draw a plot. 55 pylab.plot(range(len(deltas_ms)), deltas_ms) 56 matplotlib.pyplot.savefig("%s_deltas.png" % (NAME)) 57 58 # Test for pass/fail. 59 assert(avg > MIN_AVG_FRAME_DELTA) 60 assert(var < MAX_VAR_FRAME_DELTA) 61 assert(abs(range0) < MAX_FRAME_DELTA_JITTER) 62 assert(abs(range1) < MAX_FRAME_DELTA_JITTER) 63 64 if __name__ == '__main__': 65 main() 66 67
