drascic@ecf.UUCP (06/05/87)
I want to overlay the graphics output of a computer onto a video image of the real world, to implement a cursor. This means that I have to sync the camera to the computer's video, which is reasonably easy to do. But once I have the two signals, I have to combine. Someone suggested that "keying" was the route. This involves switching between the two signals, depending on the level of one of them. Unfortunately, this seems to be very expensive. Is it possible to simply add the two signals through appropriate resistors? Or are there chips available suitable for building a simple keyer? Any hints, suggestions, or suppliers would be much appreciated. David Drascic UUCP: drascic@ecf.toronto.edu OR drascic@utecfb
mwtilden@orchid.UUCP (06/06/87)
In article <173@mv06.ecf.toronto.edu> drascic@ecf.toronto.edu (David Drascic) writes: >Is it possible to simply add the two signals through appropriate >resistors? Or are there chips available suitable for building a >simple keyer? Any hints, suggestions, or suppliers would be much >appreciated. > When I did this a few months ago, I used a MC14052 analog mux/demux to select between the cursor-present signal and the normal video. A high grade amplifier has to re-boost the signal to 75 Ohm status but otherwise there is no distortion at all. These are all NTSC signals of course. The problem with mixing computer with video through resistors is computers generate single repeated sync signals of 262 scan lines (normally) and not the 262.5 demanded by NTSC standards. A bad jitter in your picture signal is the result along with partial to complete color loss. If you only have RGB coming out of your computer then I would recommend the MC1488 chip. Works fine with a minimum of components (the funny coils they insist you use can be easily faked with RC equivalents). I have still to get a reasonable circuit to color lock the video with this chip but I'm not worried, grey scale looks good for now. -- Mark Tilden: _-_-_-__--__--_ /(glitch!) M.F.C.F Hardware Design Lab. -_-___ | \ /\/ Un. of Waterloo. Canada, N2L-3G1 |__-_-_-| \/ work: (519)-885-1211 ext.2457, "MY OPINIONS, YOU HEAR!? MINE! MINE! MINE! MINE! MINE! AH HAHAHAHAHAHAHAHAHA!!"
asm@utcsri.UUCP (06/07/87)
In article <8037@orchid.UUCP> mwtilden@orchid.UUCP (M.W. Tilden, Hardware) writes: >[ some stuff deleted ] >If you only have RGB coming out of your computer then I would recommend the >MC1488 chip. Works fine with a minimum of components (the funny coils >^^^^^^ >they insist you use can be easily faked with RC equivalents). I have >still to get a reasonable circuit to color lock the video with this >chip but I'm not worried, grey scale looks good for now. > > >-- >Mark Tilden: _-_-_-__--__--_ /(glitch!) M.F.C.F Hardware Design Lab. >-_-___ | \ /\/ Un. of Waterloo. Canada, N2L-3G1 > |__-_-_-| \/ work: (519)-885-1211 ext.2457, >"MY OPINIONS, YOU HEAR!? MINE! MINE! MINE! MINE! MINE! AH HAHAHAHAHAHAHAHAHA!!" I think Mark means the MC1377. This is an RGB->composite video converter. -- Anees Munshi @ University of Toronto Engineering. ARPA asm%csri.toronto.edu@csnet-relay.arpa BitNet asm@utcsri.UTORONTO CSNet asm@csri.toronto.edu UUCP {allegra,ihnp4,decvax,pyramid}!utzoo!utcsri!asm Reality is so much better!
mwtilden@orchid.UUCP (06/09/87)
In article <4880@utcsri.UUCP> asm@utcsri.UUCP (Anees Munshi) writes: >In article <8037@orchid.UUCP> mwtilden@orchid.UUCP (M.W. Tilden, Hardware) writes: >>MC1488 chip. Works fine with a minimum of components (the funny coils > ^^^^ > > I think Mark means the MC1377. This is an RGB->composite video > converter. > Yes, indeed I did. Sorry about that. (What are they putting in the coffee around here?) By the way, the Motorola App Note number is AN932 if anybody's interested. -- Mark Tilden: _-_-_-__--__--_ /(glitch!) M.F.C.F Hardware Design Lab. -_-___ | \ /\/ Un. of Waterloo. Canada, N2L-3G1 |__-_-_-| \/ work: (519)-885-1211 ext.2457, "MY OPINIONS, YOU HEAR!? MINE! MINE! MINE! MINE! MINE! AH HAHAHAHAHAHAHAHAHA!!"
king@dciem.UUCP (Stephen King) (06/09/87)
You could also try looking at Motorola's MC1378, a complete video overlay synchronizer. I have put together the evaluation board, as shown in the application notes, and found it to work quite well. Some of the passive components in the circuit may be hard to find (colour burst bandpass transformer, 200nS delay line). Even the chip itself may be hard to get. (I got engineering samples from Motorola) It does, however, provide genlock, RGB input, 36Mhz clock (10x colour frequency), NTSC or PAL composite video input and overlay enable. Well worth investigating! /* these are, of course, only my own humble opinions */ ...!utzoo!dciem!king sjk.
hedley@cbmvax.cbm.UUCP (Hedley Davis) (06/10/87)
In article <173@mv06.ecf.toronto.edu> drascic@ecf.UUCP writes: >I want to overlay the graphics output of a computer onto a video image >of the real world, to implement a cursor. This means that I have to >sync the camera to the computer's video, which is reasonably easy to do. >But once I have the two signals, I have to combine. Someone suggested >that "keying" was the route. This involves switching between the two >signals, depending on the level of one of them. Unfortunately, this >seems to be very expensive. > >Is it possible to simply add the two signals through appropriate >resistors? Or are there chips available suitable for building a >simple keyer? Any hints, suggestions, or suppliers would be much >appreciated. > > David Drascic UUCP: drascic@ecf.toronto.edu OR drascic@utecfb The synchonization is the tricky part. For a simple cursor, you could probably do it with hardware of small complexity. For anything more complex, there is really only one cost effective solution. Please no flames for this ( requested ) advert. The Amiga seris of computers from Commodore support genlocking. This allows the amiga video output to be synchonized with, and overlayed upon an external composite video source ( like a camera or VCR ). The genlock then produces a composite video output ( suitable for feeding to a VCR or monitor ). If your needs are immediate, I suggest that you obtain a A1000 with a A1300 genlock ( manufactured by commodore ). If you can wait a few months the A2000 ( fancier box with better expansion capabilities ), with its genlock would be a better bet. Still later, other goodies ( as yet unannounced ) will be forth coming. On the software end, several video titlers and animiation packages are available now ( and others are RSN ). If indeed this is for the university, we have a discount program for such originizations. You might contact Dave Archambault at (215)-431-9193 about such policies. He is the man handling all the university marketing and accounts. Hedley
ex499mih@CS.UCLA.EDU (06/12/87)
IBM has recently released a piece of hardware which it calls "Infowindow". Its purpose is as a controller for level III interactive videodisc courses. One of its primary functions is to "mix" computer graphics and ntsc video on the same display. This is accomplished by using the EGA resolution mode which most closely matches the resolution of the ntsc signal (I'm no video expert, so please excuse my vagueness). Special hardware stops the EGA at the beginning of each screen refresh in order to synch it with the ntsc scan. The User (program) selects one graphics color which the hardware will consider to be "transparent" to video. As the EGA is "read" during refresh, any pel which is to have the same value as the transparent color is given the ntsc signal at that time (i.e. EGA goes to the display until transparent color, if = transparent color then NTSC). That's about it I guess.
phil@osiris.UUCP (06/15/87)
In article <6583@shemp.UCLA.EDU>, ex499mih@CS.UCLA.EDU writes: > The User (program) selects one graphics color which the hardware will > consider to be "transparent" to video. As the EGA is "read" during refresh, > any pel which is to have the same value as the transparent color is given > the ntsc signal at that time (i.e. EGA goes to the display until transparent > color, if = transparent color then NTSC). Wow, what a novel concept! :-) Suppose IBM will try to patent it? But seriously.. this sounds just like a digital form of chroma keying. (I even seem to remember someone suggesting chroma keying as a solution to the original poster's problem.) Question for all you serious broadcast people out there: I imagine the original chroma key hardware was analog. Is it still done that way, or is it done digitally now? Seems to me that with these new-fangled digital video controllers stuff like this would be getting much simpler, if not cheaper... ...!decvax!decuac!\ Phil Kos ...!seismo!mimsy!aplcen!osiris!phil The Johns Hopkins Hospital ...!allegra!/ Baltimore, MD
hedley@cbmvax.cbm.UUCP (Hedley Davis) (06/16/87)
In article <1171@osiris.UUCP> phil@osiris.UUCP (Philip Kos) writes: >Question for all you serious broadcast people out there: I imagine the >original chroma key hardware was analog. Is it still done that way, or is >it done digitally now? Seems to me that with these new-fangled digital >video controllers stuff like this would be getting much simpler, if not >cheaper... > Typically, the computer is phase locked to the incoming video signal. The actual switching is done with analogue hardware. This avoids ever having to digitize the incoming video signal ( an expensive proposition ). I've heard of full digital units which do digitize the incoming video. These often give you other bells and whistles like freeze frame, color and contrast corrections ( under software control ), and frame grabbing. They are more expensive then your run of the mill genlock. Hedley
jhma@eagle.UUCP (06/18/87)
Summary: Expires: Sender: Followup-To: The Atari ST range of computers can be genlocked: Ask Atari and I'm sure they'll be glad to tell you..... Also the old MSX ( Remember them? ) machines used a chip ( 9918? 9938? Something like that ) which had a video plane immediately in front of it's background plane and behind all the sprite planes. Try digging up a data sheet: I'm sure it's still available. Tris Mabbs. ~~~~~~~~~~~ ...!seismo!mcvax!ukc!tehm tehm@uk.ac.ukc
mwtilden@orchid.UUCP (06/22/87)
In article <3119@eagle.ukc.ac.uk> tehm@ukc.ac.uk (Tris 'Mad' Mabbs) writes: > > The Atari ST range of computers can be genlocked: Ask Atari and >I'm sure they'll be glad to tell you..... > I'm sorry but I don't think so. Sure they've included a partial hardware provision for genlocking but the way the code was implemented, it can never work. -- Mark Tilden: _-_-_-__--__--_ /(glitch!) M.F.C.F Hardware Design Lab. -_-___ | \ /\/ Un. of Waterloo. Canada, N2L-3G1 |__-_-_-| \/ work: (519)-885-1211 ext.2457, "MY OPINIONS, YOU HEAR!? MINE! MINE! MINE! MINE! MINE! AH HAHAHAHAHAHAHAHAHA!!"