Bt656_4:2:2 format vhdl code

[rajavel.rv]

Hello Friends...
i m trying to write code for bt656 4:2:2 in vhdl, i m not getting to do the chroma subsampling, could you please suggest me idea how to proceed..?

 

[TrickyDicky]

what is the source video stream? and what are you actually trying to do?

 

[rajavel.rv]

i m using ntsc(525 lines) as a video stream, i want to convert 24bit YCBCR (4:4:4) into 8-bit YCBCR (4:2:2), i m stuck up with chorma subsampling, i doesnt get idea regarding this, could u please help me...

 

[TrickyDicky]

You need to do a sliding average of Cb and Cr during the period. The output needs to be:

Y0
(Cb0+Cb-1)/2
Y1
(Cr0+Cr1)/2
Y2
(Cb2+Cb1)/2
Y3
(Cr2+Cr3)/2

--etc

 

[lucbra]

this also means that you will need a small memory to store 2 pixels (current and past)

 

[TrickyDicky]

You will also need a fifo to get the data across the clock domains as the output will be running 2x input speed.

 

[rajavel.rv]

Thanks buddy.... i m getting the ycbcr format, but now the problem is i m getting only the odd frames not the even frames, i think my problem is the line count of 525, which 3/19/240--- 3 lines for eav, sav format/ 19 lines blanking/ 240 lines ycbcr data(odd frames)
3/20/240--- 3 lines for eav, sav format/ 19 lines blanking/ 240 lines ycbcr data(even frames).. could u suggest me where i m doing mistake., but in some of the datasheets it is given as for NTSC format we have to do 262.5 scan lines... i have no idea regardin this, i m stuck up here.........

 

[TrickyDicky]

I think you mean field, not frame (a frame is made up of two fields).

How is the data you have actually formatted? is it a data stream with embedded TRS codes? or separate VSYNC and HSYNC signals?

 

[rajavel.rv]

Sorry.. its field only, wat is meant by TRS, i cant get u....
but i had used separate signal for hsync and vysnc, i m gettin hsync = 15.734hz, vsync = 59.93hz