separate Y from CbCr in YCbCr

Altera_Forum · ‎01-30-2011

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

Altera_Forum · ‎01-30-2011

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 · ‎01-31-2011

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 · ‎01-31-2011

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 · ‎01-31-2011

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

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Why input being in inverted version of its output??

I can not understand it.

Altera_Forum · ‎01-31-2011

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 · ‎02-01-2011

have you tried the Color Plane Sequencer?

Altera_Forum · ‎02-02-2011

Hi thepancake!

I am using dsp builder, quartus II v6.0, there is no color plane sequencer.

Altera_Forum · ‎02-02-2011

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 · ‎02-02-2011

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 · ‎02-02-2011

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).

Altera_Forum · ‎02-02-2011

You need Y, Cb and Cr if you are going to colour space convert to RGB. Setting Y to 0 just kills an RGB output. The conversion is done via a matrix transform. But depending on what your input and output are for affects the matrix.

Raw video off a DAC is likely to have Y values in the range 16 to 235. PC monitors often expect the range 0 to 255 for RGB for peak values, so you can either rescale the input to 0 to 255 or use a different matrix for the colour space conversion.

The standard matrix for conversion is:


(R) = ( 1.0 ,  0.0   ,  1.140 , 0.0 )   (Y )
(G) = ( 1.0 , -0.396 , -0.581 , 0.0 ) * (Cb-128)
(B) = ( 1.0 ,  2.029 ,  0.0   , 0.0))   (Cr-128)
So
R = Y + 1.14(Cr-128)
G = Y - 0.396(Cb-128) - 0.581(Cr-128)
B = Y + 2.029(Cb-128)

Altera_Forum · ‎02-03-2011

TO_BE_DONE