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Altera_Forum
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15 years ago

separate Y from CbCr in YCbCr

Hi

I have YCbCr video data in two color spaces in sequence(on the same 8bit data bus). I want to separate Y component from CbCr.

can you help me please!

thank You

12 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    If the video is 422 YCbCr you just extract every other data value with a toggling signal.

    so you get Y1 Cb1 Y2 Cr1 Y3 Cb2 Y4 Cr2 etc etc
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Thank You Tricky for again replying me!

    toggling signal??

    I am working in dsp builder v6.0.

    please guide me how is it possible in dsp builder??

    actually I want to buffer a full frame (640x480) in real time video and then I have to divide it into blockset i.e 8x8 or 16x16 or 32x32. (I have to do all this in dsp builder)

    1st of all I have to separate Y from CbCr.
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Your YCbCr signal probably has a data rate of 27MHz (pixel rate x2). You need to create a signal that toggles at 13.5MHz to pick out every Y value from the data stream, because thats how fast it change.

    All you need is a signal that looks something like this in VHDL: 

    
process(clk, reset)
begin
  if reset = '1' then
    y_valid <= '0';
  elsif rising_edge(clk)
    y_valid <= not y_valid;
  end if;
end process;

    So in DSP builder you just need a register with the input being in inverted version of its output.
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    --- Quote Start ---

    A register with the input being in inverted version of its output.

    --- Quote End ---

    Why input being in inverted version of its output??

    I can not understand it.
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    You are creating a toggle. You want to select the Y values while ignoring the C values you can use this toggle as the write enable on another register or memory.

  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Hi thepancake!

    I am using dsp builder, quartus II v6.0, there is no color plane sequencer.
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Hi Tricky!

    I have separate Y from CbCr By using 1to2 demux.

    And I made Y component to zero.

    Result is:

    The display is dark but little effects can be feel, when we move camera here and there.

    Is it prove that Y component are completely separated from CbCr????

    Thank You
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    If you separated the Y component from the input, the output would be very clearly a black and white version of the input.

    So unless you are putting a camera in a dark room, maybe you've extracted Cb/Cr instead of Y. But if you did this, you'd have a screen that was mid-grey most of the time.
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Hi Tricky!

    thanks for your guideline.

    I have made the following design flow:

    deinterlacer >> 1to2 demux(y=0,Cb and Cr = real video values) >>chroma resampler >> color space converter >> scaler megacore functions.

    So it means I have made Y=0, and play the video with just Cb and Cr values. After that I have used color space converter to make it RGB(that is connected to vga).

    I think it is fine because I set Y=0 (it means brightness=0) so output must be dark(as I brief in last post).