RGB to YPbPr

Discussion in 'Electronics Resources' started by hang-on, Dec 13, 2014.

  1. hang-on

    Thread Starter New Member

    Oct 18, 2014
    25
    1
    Hi,

    I'm researching how to convert RGBS (sync) video output to YPbPr. From Wikipedia:

    Y carries luma (brightness or luminance) and synchronization (sync) information. Y = 0.2126 R + 0.7152 G + 0.0722 B.

    I have a RGBS signals coming out of a video encoder chip (CXA1145).


    How can I - in the most simple way - generate Y from my RGB signals? I'm thinking about transistors on a breadboard, but I'm not sure how. I don't know how to add three weigthed signals together, and then 'inject' the sync signal into the result.

    It seems that I can also use op-amps, but I would prefer to use transistors. Can somebody point me in the right direction. I'm looking for pretty basic advice, as I'm quite the newbie :)
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    This type of circuits are way complicated for a n00b.
    You are better off buying a converter.

    RGB does not carry sync. For RGB sync line is separate.
     
  3. hang-on

    Thread Starter New Member

    Oct 18, 2014
    25
    1

    Hehe, yes I know I'm in over my head. But I'm totally motivated. I already have a RGBS to VGA converter + upscaler, so I can play my old video games. I'm in search of enligthenment here :)

    R,G,B and Sync are on separate lines (RGBS). Should I use voltage divider circuits on each of the RGB signals (for weighing), and then add them together, using op-amps or transistors, to get Y? (In theory)
     
  4. hang-on

    Thread Starter New Member

    Oct 18, 2014
    25
    1
    What about this approach? (Attached image). I use voltage dividers for the weighing of the three color lines, and then a summing amplifier to add them together. At the end there is a voltage inverter to invert the voltage from the summing amplifier.

    I suspect the resulting Y signal would have to be amplified... And also I need to inject the sync signal. But first things first: does the attached schematic look legit?
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    Have you looked these?
     
  6. hang-on

    Thread Starter New Member

    Oct 18, 2014
    25
    1
    Yes - thank you. I can't get the linear IC from my supplier. But most importantly I want to find an approach I can understand, and build up in steps. That is why I start with just the 'Y' :)
     
  7. hang-on

    Thread Starter New Member

    Oct 18, 2014
    25
    1
    Ron_h from this site have made a great effort on rgb to ypbpr:
    http://forum.allaboutcircuits.com/threads/signal-math-with-op-amps.79779/

    ... And I have collected a few other rgb to ypbpr schematics from around the web, and posted to another forum: http://www.smspower.org/forums/viewtopic.php?t=15048

    What I'm looking for here is not a complete guide to building a circuit. Just some feedback on my little handdrawn schematic on how to get Y without sync, from rgb signals, using voltage dividers and op amp...

    I have realized this thread is started in the wrong part of the forum. I'm sorry for the confusion. Can I move it to general electronics?
     
  8. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    Well, I'm not much on exerting effort to re-invent the wheel so, since there are many circuits out there that do what you want, I see no good reason to come up with another. But if you want to to do that, have fun.
     
    Last edited: Dec 17, 2014
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