extract only even lines from interlacer

[Altera_Forum]

hi, i have a progressive frame made by a pal frame deinterlaced with weave alghoritm. 

 now i want to extract only the original even lines of this progressive frame.   So my progressive frame is:   F0 F1 and i want => F0 F0 F0 F1    i see the altera interlacer component but i can't understand how to configure to put out only the even lines.   Is there a way to do that or i have to do an interlacer by myself?

[Altera_Forum]

Hello, 

 I have not tested this but the user guide seems to imply that the behaviour of the interlacer can be overriden under specific conditions. You need to: 1) turn on "Control packets override field selection" 2) modify the control packets on the fly and change the interlace nibble to 0000 or 0001 to select the field you want to keep  You need to write your own HDL for 2) but this seems fairly straightforward.

[Altera_Forum]

Thank you for your reply, nice idea! 

 so if i understood, i need to modify the packet nibble before entering the interlacer to have only one type of output lines (even in my case).   i need a custom component for doing that, for keeping the ready latency to 1, i need to insert a fifo too.   Maybe is more convenient to do my interlacer since i have to do the input and output streaming interface anyway

[Altera_Forum]

> i need a custom component for doing that, for keeping the ready latency to 1, i need to insert a fifo too. 

> Maybe is more convenient to do my interlacer since i have to do the input and output streaming interface anyway   I believe you could hack the interlace nibble with very simple hardware so this may be overkill. Whichever way you decide to proceed this should be helpful: http://www.alterawiki.com/wiki/vip_control_decoder

[Altera_Forum]

i tried the decoder but it has some problem when data valid in is not constant.. 

it interrupts my data flow. maybe some bug fixes needed