/
crt-mt.py
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/
crt-mt.py
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#!/usr/bin/env python
from png import Reader, Writer
from random import random
import itertools
import math
import threading
import Queue
# subcarrier frequency
Fsc=4433618.75
# line frequency
Fline=15625
# subcarrier counts per scan line = Fsc/Fline = 283.7516
# phase noise (2.5 for crappy cable)
PHASE_NOISE = 0
# use biquads to filter components, otherwise moving average
MOVING_AVERAGE = False
# Number of decoder threads
NDECODERS = 3
def nslice(s, n, truncate=False, reverse=False):
"""Splits s into n-sized chunks, optionally reversing the chunks."""
assert n > 0
while len(s) >= n:
if reverse: yield s[:n][::-1]
else: yield s[:n]
s = s[n:]
if len(s) and not truncate:
yield s
def RGBtoYUV(rgb):
r, g, b = [x / 255.0 for x in rgb]
Y = 0.299*r + 0.587*g + 0.114*b
U = 0.492*(b - Y)
V = 0.877*(r - Y)
return Y,U,V
def YUVtoRGB(y, u, v):
return y + 1.14 * v,\
y - 0.396 * u - 0.581 * v,\
y + 2.029 * u
def clamp(p):
if p < 0:
return 0
elif p > 1.0:
return 1.0
return p
class Delay:
x_2, x_3 = 0, 0
def delay(self, x):
result = self.x_3
self.x_3 = self.x_2
self.x_2 = x
return result
class Biquad:
# h/t Nigel Redmon
# http://www.earlevel.com/main/2011/01/02/biquad-formulas/
a0,a1,a2,b1,b2 = 0, 0, 0, 0, 0
x_1, x_2, y_1, y_2 = 0, 0, 0, 0
def filter(self, x):
result = self.a0*x + self.a1*self.x_1 + self.a2*self.x_2 - self.b1*self.y_1 - self.b2*self.y_2
self.x_2 = self.x_1
self.x_1 = x
self.y_2 = self.y_1
self.y_1 = result
return result
def lowpass(self, sampleRate, freq, Q):
K = math.tan(math.pi * freq/sampleRate)
norm = 1 / (1 + K / Q + K * K)
self.a0 = K * K * norm
self.a1 = 2 * self.a0
self.a2 = self.a0
self.b1 = 2 * (K * K - 1) * norm
self.b2 = (1 - K / Q + K * K) * norm
return self
def bandpass(self, sampleRate, freq, Q):
K = math.tan(math.pi * freq/sampleRate)
norm = 1.0 / (1 + K / Q + K * K)
self.a0 = K / Q * norm
self.a1 = 0.0
self.a2 = -self.a0
self.b1 = 2 * (K * K - 1) * norm
self.b2 = (1 - K / Q + K * K) * norm
return self
def notch(self, sampleRate, freq, Q):
K = math.tan(math.pi * freq/sampleRate)
norm = 1 / (1 + K / Q + K * K)
self.a0 = (1 + K * K) * norm
self.a1 = 2 * (K * K - 1) * norm
self.a2 = self.a0
self.b1 = self.a1
self.b2 = (1 - K / Q + K * K) * norm
return self
def clamp_scale(p):
if p < 0:
p = 0
elif p > 1.0:
p = 1.0
return int(p * 255)
def clamp_scale3(p):
return [clamp_scale(x) for x in p]
inputfile = 'testcard.png'
outputfile_coded = (lambda x: x[0] + '-encoded.' + x[1])(inputfile.split('.', 1))
outputfile_decoded = (lambda x: x[0] + '-decoded.' + x[1])(inputfile.split('.', 1))
width, height, pixels, meta = Reader(inputfile).asRGB8()
coded = open(outputfile_coded, 'wb')
decodedf = open(outputfile_decoded, 'wb')
coded_writer = Writer(width, height, greyscale=True)
decoded_writer = Writer(width, height)
# how many counts of Fsc
width_ratio = width / (Fsc / Fline) # ~ 2.69
delta_wt = math.pi / width_ratio
# we only get 312 lines
height_ratio = height / 312.0
print 'Files:\n input picture: %s (%dx%d)\n encoded picture: %s\n decoded picture: %s' %\
(inputfile, width, height, outputfile_coded, outputfile_decoded)
print 'Modem parameters:\n Fsc=%10.4fHz\n Line frequency=%5fHz\n Width to Fsc ratio=%3.3f' % (Fsc, Fline, width_ratio)
#result=[]
#result_decoded=[]
# pixelline=0
halfpi = math.pi / 2
class Encoder (threading.Thread):
def __init__(self, queue, pixels):
threading.Thread.__init__(self)
self.queue = queue
self.pixels = pixels
self.result = []
def Encode(self, rgb, sinwt, coswt):
y,u,v = RGBtoYUV(rgb)
return clamp(y + u * sinwt + v * coswt)
def run(self):
pixelline = 0
for linepixels in self.pixels:
line = int(round(pixelline / height_ratio)) % 2
wt = (180.0 + [+90,-90][line]) / 180.0 * math.pi
yavg, uavg, vavg = 0, 0, 0
t = 0
encoded = [0] * width
decoded = [0] * width * 3
for inputrgb in nslice(linepixels, 3):
wt = t * 2 * math.pi / width_ratio + [ +halfpi, -halfpi][line]
sinwt = math.sin(wt)
coswt = math.cos(wt) # * [+1,-1][line]
pal = self.Encode(inputrgb, sinwt, coswt)
encoded[t] = int(pal * 255)
t = t + 1
self.result.append(encoded)
#print 'Encoder puts line %d' % pixelline
self.queue.put((pixelline, encoded))
pixelline = pixelline + 1
# ensure that all consumers get their termination flags
self.queue.put((-1, None))
self.queue.put((-1, None))
self.queue.put((-1, None))
self.queue.put((-1, None))
NextDecoderId = 0
class Decoder(threading.Thread):
def __init__(self, queue, result):
threading.Thread.__init__(self)
self.queue = queue
self.result = result
global NextDecoderId
self.id = NextDecoderId
NextDecoderId = NextDecoderId + 1
# chroma filter
self.fitler = Biquad().bandpass(Fsc * width_ratio, Fsc, 0.7) # 1.7 looks kinda cool in a wrong way
# luma filter
self.notch = Biquad().notch(Fsc * width_ratio, Fsc, 0.7)
# chroma output smoothing filter
self.fitlerU = Biquad().lowpass(Fsc * width_ratio, Fsc*0.2, 0.7)
self.fitlerV = Biquad().lowpass(Fsc * width_ratio, Fsc*0.2, 0.7)
self.yavg, self.uavg, self.uavg = 0, 0, 0
def Decode(self, pal, sinwt, coswt):
if MOVING_AVERAGE:
self.yavg = (yavg + pal) / 2.0
y_ = yavg
u_ = (pal - y_) * 2 * sinwt
v_ = (pal - y_) * 2 * coswt
self.uavg = (uavg + u_) / 2
self.vavg = (vavg + v_) / 2
u_ = uavg
v_ = vavg
else:
color = self.fitler.filter(pal)
y_ = self.notch.filter(pal) # - color
u_ = color * 2 * sinwt
v_ = color * 2 * coswt
u_ = self.fitlerU.filter(u_)
v_ = self.fitlerV.filter(v_)
return YUVtoRGB(y_, u_, v_)
def run(self):
while True:
pixelline, encoded = self.queue.get(True)
#print 'Decoder %d picked line %d, qsize=%d' % (self.id, pixelline, self.queue.qsize())
if pixelline == -1:
break
t = 0
decoded = [0] * width * 3
line = int(round(pixelline / height_ratio)) % 2
for pal in encoded:
wt = t * 2 * math.pi / width_ratio + [ +halfpi, -halfpi][line]
sinwt = math.sin(wt)
coswt = math.cos(wt) # * [+1,-1][line]
r, g, b = self.Decode(pal/255.0, sinwt, coswt)
decoded[t*3:t*3+3] = clamp_scale3([r,g,b])
t = t + 1
self.result[pixelline] = decoded
workQueue = Queue.Queue(10)
encoder = Encoder(workQueue, pixels)
decoderResult = [None] * height
decoders = [None] * NDECODERS
for i in xrange(NDECODERS):
decoders[i] = Decoder(workQueue, decoderResult)
print 'Decoding using %d decoders' % (len(decoders))
encoder.start()
for decoder in decoders:
decoder.start()
encoder.join()
print 'Encoding terminated, waiting for the decoders to finish'
for decoder in decoders:
decoder.join()
print 'Decoding terminated'
coded_writer.write(coded, encoder.result)
decoded_writer.write(decodedf, decoderResult)