Video overlay

Delus

I'm sure i've seen a thread which mentions this topic somewhere but can't for the life of me so i hope this hasn't been addressed already.··I'm wondering if it is possible to take an RCA signal from a camera and add a preprogrammed message and simple graphic(could be·just lines and circles) to it in real time using the prop.· I'm a pretty new to video signals so any pointers(no matter how basic they seem) would be greatly appreciated.

Ziggy252

http://forums.parallax.com/showthread.php?p=635949

Prop based OSD module

Oldbitcollector (Jeff)

This applies too..

http://forums.parallax.com/showthread.php?p=618061

OBC

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Just getting started with Propeller?

Propeller Cookbook

PropDOS

Delus

Thank you very much this looks almost exactly like what i need.· one somewhat minor point is how would one go about getting some colours out of this system?·pure red or green are the only two i need but i see that the HC-OSD board claims to only do black, grey,·and white.

Mike Green

Synchronizing color between a background and an overlay is much more difficult than simply overlaying a black and white image or text.

Bean

Delus,
To do color overlay requires a circuit that can "lock" onto the incoming color burst pulse. This is not an easy thing to do.

The HC-OSD pixels can have one of 4 states: transparent, black, white, or gray.

Bean

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www.iElectronicDesigns.com

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Delus

Ok i've been looking at various other solutions to this problem and stumbled across a video multiplexer (http://www.fairchildsemi.com/ds/FH%2FFHP3194.pdf) which might do the trick by just swiching between a signal generated by the prop and an input signal at the apropriate pixels.· So my question now is how do i find out if it will swich fast enough?· And how do i synchronize the signal generated by the prop?

Phil Pilgrim (PhiPi)

You don't need anything that fancy. I've used a 74HC4053 for overlay switching, and it works just fine. (Even a CD4053 will work if you don't mind a little fuzz around the edges.)

-Phil

Mike Green

An external video multiplexor will not help you. The problem is the synchronization of the Propeller's video generator with the external video signal. This is easy to do for superimposing black and white on color, but very hard for color on color. The way the HC-OSD works, the Propeller effectively disconnects itself from the video circuit when it's not overlaying video on the external image, so no external multiplexor is needed.

Phil Pilgrim (PhiPi)

Maybe Bean can shed some light here:

I've always used a multiplexer for switching overlay data in and out of the video signal, after it's been DC restored to keep the sync tips near ground. This gives me known voltage levels for sync, front- and back-porch, black, and white that I can match with the multiplexed signal from the computer. From there, the output is then buffered with a simple transtor buffer to restore the 75-ohm impedance.

Bean seems to have circumvented the DC restoration, multiplexing, and buffering in his design by using more of a forced superposition; so I'm wondering what, if any, assumptions he's making about the incoming video signal... Bean?

-Phil

Post Edited (Phil Pilgrim (PhiPi)) : 12/7/2007 11:28:30 PM GMT

Drone

Delus,

Recently there was a post here from Bean I think that described the MAX7456 chip, which seems to do B&W (only) video overlay. Looks good for putting time/date stamps and/or GPS data on a screen. Bean even had some breakout boards available, but when I inquired about how to buy, things fizzled out. I'll find the thread - but have to run right now. Here's the URL for the MAX7456 press release and technical page:

www.maxim-ic.com/view_press_release.cfm/release_id/1376

www.maxim-ic.com/quick_view2.cfm/qv_pk/5516

Regards,

David