kopia lustrzana https://github.com/dnet/pySSTV
87 wiersze
2.3 KiB
Python
87 wiersze
2.3 KiB
Python
#!/usr/bin/env python
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from __future__ import division, with_statement
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from math import sin, pi, floor
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from random import random
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from contextlib import closing
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import struct, wave
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FREQ_VIS_BIT1 = 1100
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FREQ_SYNC = 1200
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FREQ_VIS_BIT0 = 1300
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FREQ_BLACK = 1500
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FREQ_VIS_START = 1900
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FREQ_WHITE = 2300
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FREQ_RANGE = FREQ_WHITE - FREQ_BLACK
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MSEC_VIS_START = 300
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MSEC_VIS_SYNC = 10
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MSEC_VIS_BIT = 30
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class SSTV(object):
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def __init__(self, image, samples_per_sec, bits):
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self.image = image
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self.samples_per_sec = samples_per_sec
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self.bits = bits
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BITS_TO_STRUCT = {8: 'b', 16: 'h'}
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def write_wav(self, filename):
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fmt = '<' + self.BITS_TO_STRUCT[self.bits]
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data = ''.join(struct.pack(fmt, b) for b in self.gen_samples())
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with closing(wave.open(filename, 'wb')) as wav:
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wav.setnchannels(1)
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wav.setsampwidth(self.bits // 8)
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wav.setframerate(self.samples_per_sec)
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wav.writeframes(data)
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def gen_samples(self):
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"""generates bits from gen_values"""
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max_value = 2 ** self.bits
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alias = 1 / max_value
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amp = max_value / 2
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lowest = -amp
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highest = amp - 1
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for value in self.gen_values():
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sample = int(round(value * amp + alias * (random() - 0.5)))
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yield max(min(highest, sample), lowest)
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def gen_values(self):
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"""generates -1 .. +1 values from freq_bits"""
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spms = self.samples_per_sec / 1000
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param = 0
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samples = 0
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for freq, msec in self.gen_freq_bits():
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offset = param
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samples += spms * msec
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tx = floor(samples)
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for sample in xrange(int(tx)):
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t = sample / self.samples_per_sec
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param = t * freq * 2 * pi + offset
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yield sin(param)
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samples -= tx
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def gen_freq_bits(self):
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"""generates (freq, msec) tuples from image"""
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yield FREQ_VIS_START, MSEC_VIS_START
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yield FREQ_SYNC, MSEC_VIS_SYNC
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yield FREQ_VIS_START, MSEC_VIS_START
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yield FREQ_SYNC, MSEC_VIS_BIT # start bit
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vis = self.VIS_CODE
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num_ones = 0
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for _ in xrange(7):
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bit = vis & 1
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vis >>= 1
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num_ones += bit
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bit_freq = FREQ_VIS_BIT1 if bit == 1 else FREQ_VIS_BIT0
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yield bit_freq, MSEC_VIS_BIT
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parity_freq = FREQ_VIS_BIT1 if num_ones % 2 == 1 else FREQ_VIS_BIT0
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yield parity_freq, MSEC_VIS_BIT
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yield FREQ_SYNC, MSEC_VIS_BIT # stop bit
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def horizontal_sync(self):
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yield FREQ_SYNC, self.SYNC
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def byte_to_freq(value):
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return FREQ_BLACK + FREQ_RANGE * value / 255
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