Re: [Discuss-gnuradio] working example gnuradio TV receiver for NTSC and PAL (black and white)

[Prateek Dayal]

Great ..... I will try to build on this and add sync information to
the decoding.

 I am thinking that we can collect some data that approximately
corresponds to atleast one frame, then parse it to note the position
of H and V sync pulses and then with this information parse it again
to build a frame. That way even if as you told, the lines are not
constant length, we should be able to decode, with the pixels for the
remaining missing info put to something like black ....

Regards,

Prateek


On Thu, 06 Jan 2005 06:26:49 +0100, Martin Dvh
<address@hidden> wrote:
> Hi all,
> The discussion about the NTSC reception inspired me to write an example and 
> it works.
> http://www.olifantasia.com/projects/gnuradio/mdvh/examples/mdvh14_ntsc_demod.py
> 
> It get recognisable pictures in my setup.
> http://www.olifantasia.com/projects/gnuradio/ntsc_out_raw_short1.jpg
> http://www.olifantasia.com/projects/gnuradio/ntsc_out_raw_short.gray
> 
> I used the following commandline to get these pictures:
> ./mdvh14_ntsc_demod.py 11.0625 -20.0 -22 708.25
> and used the following to show the results:
> display -depth 16 -size 400x625  ntsc_out_raw_short.gray
> 
> My rf frontend has a much too wide bandwidth (no saw filter yet) but I do get 
> a picture.
> my setup: 38.9 Mhz IF
>            50 Msps 8 bit ADC
> The IF of 38.9 Mhz folds back to 11.0625 Mhz
> 
> You get black and white only.
> 
> Greetings,
> Martin
> 
> #!/usr/bin/env python
> #
> # Copyright 2004 Free Software Foundation, Inc.
> #
> # This file is part of GNU Radio
> #
> # GNU Radio is free software; you can redistribute it and/or modify
> # it under the terms of the GNU General Public License as published by
> # the Free Software Foundation; either version 2, or (at your option)
> # any later version.
> #
> # GNU Radio is distributed in the hope that it will be useful,
> # but WITHOUT ANY WARRANTY; without even the implied warranty of
> # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> # GNU General Public License for more details.
> #
> # You should have received a copy of the GNU General Public License
> # along with GNU Radio; see the file COPYING.  If not, write to
> # the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
> # Boston, MA 02111-1307, USA.
> #
> 
> from gnuradio import gr
> from gnuradio import audio
> #from gnuradio import ssrp
> from gnuradio import mc4020
> import sys
> 
> def build_graph (freq,rffreq,sfactor,black_level):
>          #sampling_freq = 35468950
>          sampling_freq = 50000000.0
>          demod_rate=6e6
>          video_rate=6e6
> 
>          flags=mc4020.BTTV_INPUT_1 |mc4020.BTTV_EXTEND_RAW_LINES 
> |mc4020.BTTV_NOGAP
>          # | mc4020.BTTV_DEC3 |mc4020.BTTV_DO_NOT_EMULATE_AC_COUPLING 
> |mc4020.BTTV_OUTPUT_MULTIPLE
>          if((flags & mc4020.BTTV_DEC3)==mc4020.BTTV_DEC3):
>             sampling_freq=sampling_freq/3 #sampling_freq=11822983.0
> 
>          #src0 = ssrp.source_f(0)
>          #src0 = gr.file_source(gr.sizeof_short, "input_signal.raw")
>          #My own driver for my own hacked bttv card to have functionality 
> similar to mc4020
>          src0 = mc4020.source (sampling_freq,flags, "/dev/video0");
> 
>          cfir_decimation=int(sampling_freq/(8*demod_rate))*8 # = 368
>          demod_rate=sampling_freq/cfir_decimation
>          pixels_in_line_pal=demod_rate/(25*625)
>          pixels_in_line_ntsc=demod_rate/(30*525)
>          fg = gr.flow_graph ()
> 
>          if rffreq>0.0:
>              actualtunerfreq=src0.set_RF_freq(rffreq)
>              freq=freq+(rffreq - actualtunerfreq)
> 
>          adj_in = gr.add_const_ss(0)  #dummy adj_in does nothing (add 0 to 
> the signal) but has a big effect on the minimal bandwith of the fir
> filter I can use
>          # compute FIR filter taps
>          channel_coeffs = \
>                  gr.firdes.low_pass (
>                    1.0,                  # gain
>                    sampling_freq,
>                    1e6,                 # low pass cutoff
>                    3e6,                 # width of transition band
> 
>                    gr.firdes.WIN_HAMMING )
> 
>          # input: short; output: complex
>          chan_filter1 = \
>                  gr.freq_xlating_fir_filter_scf (
>                    cfir_decimation,
>                    channel_coeffs,
>                    freq,
>                    sampling_freq )
> 
>          am_demod = gr.complex_to_mag ()
> 
>          dc_restore = gr.add_const_ff(black_level)
>          #dc_restore = gr.add_const_ss(black_level)
> 
>          scale = gr.multiply_const_ff (sfactor)
> 
>          #video_lp_coeffs = gr.firdes.low_pass (
>          #        1, video_rate, 1e6, 6e6,
>          #        gr.firdes.WIN_HAMMING )
>          #
>          #video_lp = gr.fir_filter_fff (int(video_rate/demod_rate), 
> video_lp_coeffs )
> 
>          float_to_short=gr.float_to_short()
> 
>          dst = gr.file_sink (gr.sizeof_short, "ntsc_out_raw_short.gray")#raw 
> file with short image data, not synchronized yet
> 
>          fg.connect ( src0, adj_in )
>          fg.connect(adj_in,chan_filter1)
>          fg.connect ( chan_filter1, am_demod )
>          fg.connect(am_demod,scale)
>          fg.connect(scale,dc_restore)
>          fg.connect(dc_restore,float_to_short)
>          fg.connect(float_to_short,dst)
> 
>          print "You can use the imagemagick display tool to show the 
> resulting imagesequence"
>          print "use the following line to show a PAL signal:"
>          print "display -depth 16 -size " +str(int(pixels_in_line_pal))+ 
> "x625  gray:ntsc_out_raw_short.gray"
>          print "use the following line to show a NTSC signal:"
>          print "display -depth 16 -size " +str(int(pixels_in_line_ntsc))+ 
> "x525  gray:ntsc_out_raw_short.gray"
> 
>          return fg
> 
> def main (args):
> 
>          nargs = len (args)
>          rffreq=0.0
>          if nargs == 4:
>                  rffreq=float (args[3])* 1e6
>          if ((nargs == 3) | (nargs==4)):
>                  freq=float (args[0])* 1e6
>                  sfactor=float (args[1])
>                  black_level=float(args[2])
>          else:
>                  sys.stderr.write ('usage: ntsc_demod.py iffreq  scale 
> black_levelcorrection [rffreq]\n')
>                  sys.stderr.write ('frequencies in Mhz\n')
>                  sys.stderr.write ('Using an 8 bit ADC and an iffreq of 38.9 
> Mhz (folded back to 11.0625 when using 50 Mhz sampling_freq), a
> scale factor of -20.0 and a blacklevelcorrection of -22 gave me a reasonable 
> picture for a PAL signal\n')
>                  sys.stderr.write ('For NTSC I think you need to use a 
> positive scale factor\n')
>                  sys.exit (1)
>          fg = build_graph(freq,rffreq,sfactor,black_level)
>          fg.start()
>          raw_input ('Press Enter to quit')
>          fg.stop()
> 
> if __name__ == '__main__':
>          main (sys.argv[1:])
> 
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> 


-- 
Prateek Dayal
B.Tech 4th Year
ECE
IIT Guwahati

www.geocities.com/pmd_iitgw