131 lines
2.7 KiB
Python
131 lines
2.7 KiB
Python
#!/usr/bin/env python3
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import matplotlib.pyplot as plt
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import struct
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from PIL import Image
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IMG_WIDTH = 640
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SYNC_LENGTH = 105
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SYNC_THRESH = 100
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PORCH_LENGTH = 10
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LINE_LENGTH = SYNC_LENGTH + PORCH_LENGTH + 4 * IMG_WIDTH
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MAX_DEV = 600
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CENTER = 1750
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MIN_FREQ = 1200
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MAX_FREQ = 2300
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COLOR_LOW = 1500
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COLOR_HIGH = MAX_FREQ
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def to_freq(sample):
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freq = CENTER + sample * MAX_DEV
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freq = max(MIN_FREQ, freq)
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freq = min(MAX_FREQ, freq)
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return freq
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def to_color(sample):
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sample = (sample - 1500) / (COLOR_HIGH - COLOR_LOW)
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sample = int(sample * 255)
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sample = max(sample, 0)
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sample = min(sample, 255)
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return sample
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def ycbcr_to_rgb(y, cb, cr):
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r = int(y + 1.402 * (cr - 128))
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g = int(y - 3.44136 * (cb - 128) - 0.714136 * (cr - 128))
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b = int(y + 1.772 * (cb - 128))
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return (r,g,b)
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last_sync = False
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def is_sync(backlog):
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global last_sync
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count = 0
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for sample in backlog:
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if sample < COLOR_LOW:
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count += 1
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res = False
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if count > SYNC_THRESH and not last_sync:
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res = True
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last_sync = count > SYNC_THRESH
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return res
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def render_lines(line):
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pixels = [[(0,0,0)] * IMG_WIDTH, [(0,0,0)] * IMG_WIDTH]
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# Strip porch
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porch = len(line) - SYNC_LENGTH - 4 * IMG_WIDTH
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if porch < 0:
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return pixels
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line = line[PORCH_LENGTH:]
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for i in range(0, IMG_WIDTH):
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y0 = to_color(line[i])
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cr = to_color(line[IMG_WIDTH + i])
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cb = to_color(line[2 * IMG_WIDTH + i])
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y1 = to_color(line[3 * IMG_WIDTH + i])
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pixels[0][i] = y0, cb, cr
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pixels[1][i] = y1, cb, cr
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return pixels
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def main():
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data_file = open("demod.dat", 'rb')
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samples = []
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syncs = []
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pixels = []
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backlog = [0.0] * SYNC_LENGTH
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line = []
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bytes = data_file.read(4)
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while len(bytes) == 4:
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sample = struct.unpack('f', bytes)[0]
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sample = to_freq(sample)
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samples += [sample]
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backlog = backlog[1:] + [sample]
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line += [sample]
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if is_sync(backlog) or len(line) > LINE_LENGTH:
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if len(line) > SYNC_LENGTH + 4 * IMG_WIDTH:
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syncs += [1000]
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print("%d \t %d" % (len(line), len(line) - LINE_LENGTH))
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pixels += render_lines(line)
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else:
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print("Short line dropped")
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line = []
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else:
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syncs += [0]
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bytes = data_file.read(4)
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plt.plot(samples)
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plt.plot(syncs)
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plt.show()
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img = Image.new('YCbCr', (IMG_WIDTH, len(pixels)))
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img_pix = img.load()
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for x in range(0, IMG_WIDTH):
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for y in range(0, len(pixels)):
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img_pix[x,y] = pixels[y][x]
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img = img.convert('RGB')
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img.save('output.png')
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if __name__ == '__main__':
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main()
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