ValueError: Digital filter critical frequencies must be 0 < Wn < 1

[luistelmocosta]

First, thank you for this amazing project. The results look very promsing!

However, I am getting this error a lot and I really don't know what is triggering it and how to solve it.

C:\Users\luis.s.costa\AppData\Local\Continuum\anaconda3\envs\HR_measurement\lib\site-packages\numpy\core\fromnumeric.py:3257: RuntimeWarning: Mean of empty slice.
  out=out, **kwargs)
C:\Users\luis.s.costa\AppData\Local\Continuum\anaconda3\envs\HR_measurement\lib\site-packages\numpy\core\_methods.py:161: RuntimeWarning: invalid value encountered in double_scalars
  ret = ret.dtype.type(ret / rcount)
Traceback (most recent call last):
  File "GUI.py", line 273, in run
    self.main_loop()
  File "GUI.py", line 222, in main_loop
    self.process.run()
  File "C:\Users\luis.s.costa\Documents\201912.HeartRateMeasurement\Heart-rate-measurement-using-camera-master\process.py", line 106, in run
    processed = self.butter_bandpass_filter(processed,0.8,3,self.fps,order = 3)
  File "C:\Users\luis.s.costa\Documents\201912.HeartRateMeasurement\Heart-rate-measurement-using-camera-master\process.py", line 151, in butter_bandpass_filter
    b, a = self.butter_bandpass(lowcut, highcut, fs, order=order)
  File "C:\Users\luis.s.costa\Documents\201912.HeartRateMeasurement\Heart-rate-measurement-using-camera-master\process.py", line 145, in butter_bandpass
    b, a = signal.butter(order, [low, high], btype='band')
  File "C:\Users\luis.s.costa\AppData\Local\Continuum\anaconda3\envs\HR_measurement\lib\site-packages\scipy\signal\filter_design.py", line 2867, in butter
    output=output, ftype='butter', fs=fs)
  File "C:\Users\luis.s.costa\AppData\Local\Continuum\anaconda3\envs\HR_measurement\lib\site-packages\scipy\signal\filter_design.py", line 2346, in iirfilter
    raise ValueError("Digital filter critical frequencies "
ValueError: Digital filter critical frequencies must be 0 < Wn < 1

Everything worls flawlessly, I just want a workaround to avoid this error. One idea could be use the previous value in the case this error appears. 

Any idea how to fix this?

[dorukkarinca]

~~This has to do with the fps being 0, which results in a division-by-zero in butter_bandpass~~

Correction: this has to do with the fps being not large enough. You need to raise the fps to 6 or above by one or more of:

• retrying on a faster computer
• retrying after closing high-CPU apps
• retrying after cooling down your computer (e.g. moving to a cooler room)
• reducing the input resolution
• trying a pre-recorded video instead of a webcam feed