From 244d141be84becd838cc8834cec5a71c02e8d820 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A1s=20Veres-Szentkir=C3=A1lyi?= <vsza@vsza.hu>
Date: Thu, 23 May 2013 13:53:47 +0200
Subject: [PATCH] first working Robot 8 B/W version

---
 sstv.py | 105 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 105 insertions(+)
 create mode 100644 sstv.py

diff --git a/sstv.py b/sstv.py
new file mode 100644
index 0000000..aeca878
--- /dev/null
+++ b/sstv.py
@@ -0,0 +1,105 @@
+#!/usr/bin/env python
+
+from __future__ import division, with_statement
+from math import sin, asin, pi
+from random import random
+import struct
+
+FREQ_VIS_BIT1 = 1100
+FREQ_SYNC = 1200
+FREQ_VIS_BIT0 = 1300
+FREQ_BLACK = 1500
+FREQ_VIS_START = 1900
+FREQ_WHITE = 2300
+FREQ_RANGE = FREQ_WHITE - FREQ_BLACK
+
+MSEC_VIS_START = 300
+MSEC_VIS_SYNC = 10
+MSEC_VIS_BIT = 30
+
+ROBOT_BW_8_WIDTH = 160
+ROBOT_BW_8_HEIGHT = 120
+ROBOT_BW_8_SYNC = 10
+ROBOT_BW_8_SCAN = 56
+ROBOT_BW_8_VIS = 0x02
+
+class SSTV(object):
+	def __init__(self, image, samples_per_sec, bits):
+		self.image = image
+		self.samples_per_sec = samples_per_sec
+		self.bits = bits
+
+	BITS_TO_STRUCT = {8: 'b', 16: 'h'}
+	def write_wav(self, filename):
+		bytes_per_sec = self.bits // 8
+		fmt = '<' + self.BITS_TO_STRUCT[self.bits]
+		data = ''.join(struct.pack(fmt, b) for b in self.gen_samples())
+		payload = ''.join((
+				'WAVE',
+				'fmt ',
+				struct.pack('<IHHIIHH', 16, 1, 1, self.samples_per_sec,
+					self.samples_per_sec * bytes_per_sec, bytes_per_sec,
+					self.bits),
+				'data',
+				struct.pack('<I', len(data))
+				))
+		header = 'RIFF' + struct.pack('<I', len(payload) + len(data))
+		with file(filename, 'wb') as wav:
+			wav.write(header)
+			wav.write(payload)
+			wav.write(data)
+
+	def gen_samples(self):
+		"""generates bits from gen_values"""
+		max_value = 2 ** self.bits
+		alias = 1 / max_value
+		amp = max_value / 2
+		lowest = -amp
+		highest = amp - 1
+		for value in self.gen_values():
+			sample = int(round(value * amp + alias * random()))
+			yield max(min(highest, sample), lowest)
+
+	def gen_values(self):
+		"""generates -1 .. +1 values from freq_bits"""
+		spms = self.samples_per_sec / 1000
+		param = 0
+		for freq, msec in self.gen_freq_bits():
+			offset = param
+			for sample in xrange(int(round(spms * msec + random()))):
+				t = sample / self.samples_per_sec
+				param = t * freq * 2 * pi + offset
+				yield sin(param)
+
+	def gen_freq_bits(self):
+		"""generates (freq, msec) tuples from image"""
+		yield FREQ_VIS_START, MSEC_VIS_START
+		yield FREQ_SYNC, MSEC_VIS_SYNC
+		yield FREQ_VIS_START, MSEC_VIS_START
+		yield FREQ_SYNC, MSEC_VIS_BIT # start bit
+		vis_code = ROBOT_BW_8_VIS
+		num_ones = 0
+		for bitnum in xrange(7):
+			bit = (vis_code >> bitnum) & 1
+			num_ones += bit
+			bit_freq = FREQ_VIS_BIT1 if bit == 1 else FREQ_VIS_BIT0
+			yield bit_freq, MSEC_VIS_BIT
+		parity_freq = FREQ_VIS_BIT1 if num_ones % 2 == 1 else FREQ_VIS_BIT0
+		yield parity_freq, MSEC_VIS_BIT
+		yield FREQ_SYNC, MSEC_VIS_BIT # stop bit
+		msec_pixel = ROBOT_BW_8_SCAN / ROBOT_BW_8_WIDTH
+		image = self.image
+		for line in xrange(ROBOT_BW_8_HEIGHT):
+			yield FREQ_SYNC, ROBOT_BW_8_SYNC
+			for col in xrange(ROBOT_BW_8_WIDTH):
+				pixel = image.getpixel((col, line))
+				value = sum(pixel) / len(pixel)
+				freq_pixel = FREQ_BLACK + FREQ_RANGE * value / 256
+				yield freq_pixel, msec_pixel
+
+
+if __name__ == '__main__':
+	from PIL import Image
+	image = Image.open('160x120bw.png')
+	s = SSTV(image, 48000, 16)
+	s.write_wav('test.wav')