videofiltresampkey.py

#Program to capture a video from a camera, filter is, and display it live on the screen
#Gerald Schuller, October 2014

import numpy as np
import scipy.signal
import cv2

#Downsample factor:
N=8

cap = cv2.VideoCapture(0)
[retval, frame] = cap.read()
[r,c,d]=frame.shape
print(r,c)
Dsy=np.zeros((r,c));


#2D-Mask to set to zero the 7/8 highest frequencies, 
#only kep the 1/8 lowest frequencies in each direction:
M=np.ones((r,c))
M[(r//16):(r-r//16),(c//16):(c-c//16)]=np.zeros((int(7/8*r),int(7/8*c)));
#Conmpute space-domain/inverse 2D Fourier transform of Low Pass filter:
h=np.abs(np.fft.ifft2(M))
hc=np.concatenate((h[:,(c//2):c],h[:,0:(c//2)]),axis=1)
hc=np.concatenate((hc[(r//2):r,:],hc[0:(r//2),:]))
#Only keep the part with the biggest components to reduce computations:
hc=hc[(r//2-4):(r//2+4),(c//2-4):(c//2+4)]
#filt=hc

#High pass filter kernel for edge detection:
#filt=np.matrix([[-1.0,-1.0,-1],[-1,8,-1],[-1,-1,-1]])/1.0;
#Low Pass Kernel:
#rectangular filter kernel:
filt1=np.ones((8,8))/8;
#Triangular filter kernel:
filt2=scipy.signal.convolve2d(filt1,filt1)/8

filteron=False;
#Filter type:
rectfilt=True;

while(True):
    # Capture frame-by-frame
    [ret, frame] = cap.read()
    Y=(0.114*frame[:,:,0]+0.587*frame[:,:,1]+0.299*frame[:,:,2])/256; 
    cv2.imshow('Original Y Signal',Y)

    if rectfilt==True:
       filt=filt1;
    else:
       filt=filt2;

    if filteron == True:
       Y=scipy.signal.convolve2d(Y,filt,mode='same')
    #Downsample filtered frame:
    Dsy[0::N,::N]=Y[0::N,::N]; 
    # Display the resulting filtered frame
    #cv2.imshow('Y LP filtered, down- and upsampled',Dsy)
    #low pass filter the downsampled version to fill picture:
    
    if filteron==True:
       yfilt=scipy.signal.convolve2d(Dsy,filt,mode='same')
    else:
       yfilt=Dsy.copy()
    #print(Dsy[0:8,0:8])
    cv2.putText(yfilt,"Down- and upsampling and LP filtering Demo", (20,50), cv2.FONT_HERSHEY_SIMPLEX, 0.8, (255,128,128))
    cv2.putText(yfilt,"Toggle LP filter on/off: key f", (20,100), cv2.FONT_HERSHEY_SIMPLEX, 0.8, (255,128,128))
    cv2.putText(yfilt,"Toggle rect and triang filt. kernel: key t", (20,150), cv2.FONT_HERSHEY_SIMPLEX, 0.8, (255,128,128))
    cv2.putText(yfilt,"Quit: key q", (20,200), cv2.FONT_HERSHEY_SIMPLEX, 0.8, (255,128,128))
    cv2.imshow('(LP filtered,) down- and upsampled (, and LP filtered)',yfilt)
    key=cv2.waitKey(1) & 0xFF;
    if key == ord('f'):
       filteron= not filteron;
    if key == ord('t'):
       rectfilt= not rectfilt;
    if key == ord('q'):
        break

# When everything done, release the capture
cap.release()
cv2.destroyAllWindows()