Script to extract a picture from a BT.656 frame

convert_from_bt656.py

#! /usr/bin/python

###############################################################################
#  Script converts a single frame, compliant with ITU-R BT.656-5,
#      into a picture of given format (like PNG, JPEG, BMP, etc)
#
#  Tested with Python 2.7.5, Pillow 2.7
###############################################################################

from PIL import Image
import sys

THE_FIRST_LINE_ON_TOP = False
LINES, ACTIVE_LINES, TOTAL_SAMPLES = 625, 576, 864
ACTIVE_SAMPLES = 720


def is_active(line):
    return not(line < 23 or (311 <= line < 336) or (624 <= line))


# equations are from http://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.601_conversion
def ycbcr_to_rgb(luma, chroma_blue, chroma_red):
    luma_m = 298.082 * luma
    red = (luma_m + 408.583 * chroma_red) / 256 - 222.921
    green = (luma_m - 100.291 * chroma_blue - 208.120 * chroma_red) / 256 + 135.576
    blue = (luma_m + 516.412 * chroma_blue) / 256 - 276.836
    return int(red), int(green), int(blue)


def convert_to_picture(frame):
    # group bytes into lines
    line_length = TOTAL_SAMPLES * 2
    offset = (TOTAL_SAMPLES - ACTIVE_SAMPLES) * 2
    frame = [frame[i:i + line_length] for i in range(offset, len(frame), line_length)]
    # list of active lines
    active = [line for line in range(1, LINES + 1) if is_active(line)]
    half = len(active) / 2
    if THE_FIRST_LINE_ON_TOP:
        ordered_lines = [x for sub in zip(active[0:half], active[half:]) for x in sub]
    else:
        ordered_lines = [x for sub in zip(active[half:], active[0:half]) for x in sub]
    image = Image.new('RGB', (ACTIVE_SAMPLES, ACTIVE_LINES))
    for i, line in enumerate(ordered_lines):
        samples = [int(sample) for sample in frame[line]]
        for j in range(0, ACTIVE_SAMPLES, 2):
            chroma_blue, luma0, chroma_red, luma1 = samples[j * 2:j * 2 + 4]
            image.putpixel((j, i), ycbcr_to_rgb(luma0, chroma_blue, chroma_red))
            image.putpixel((j + 1, i), ycbcr_to_rgb(luma1, chroma_blue, chroma_red))
    return image


def main():
    if len(sys.argv) < 3:
        print "Usage: %s <frame> <output with extension>" % sys.argv[0]
        exit(0)

    frame = []
    try:
        frame_file = open(sys.argv[1], 'rt')
        frame = frame_file.readlines()
        frame_file.close()
    except IOError:
        print 'Cannot open frame file'
        exit(1)

    if len(frame) != LINES * TOTAL_SAMPLES * 2:
        print("Wrong size of frame: actual size - %d value(s), expected %d values" %
              (len(frame), LINES * TOTAL_SAMPLES * 2))
        exit(1)

    image = convert_to_picture(frame)

    print "Frame converted"
    try:
        image.save(sys.argv[2])
    except KeyError:
        print "Error: Cannot decide on picture format"
        exit(1)
    except IOError:
        print "Error: Cannot save output"
        exit(1)
    print "Written to %s" % sys.argv[2]


if __name__ == '__main__':
    main()

Great job, I will try it in my project and will give you feed back

Thank you