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 MSG:FROM: SPGDCM  --UCBCMSA  TO: NETWORK --NETWORK           05/24/88 18:10:06
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 From: Doug Mosher
 Subject: Re: frame buffers for digital vcr's

 To: rec-video@ucbvax sci-electronics@ucbvax

  >Doug Mosher asks, in rec.video:
  >
  > An interesting realization dawned on me. Many contemporary VCR's (and some
  > TV's) provide special effects (such as freeze-frame) by converting and
  storing
  > a video frame in some kind of digital storage (some sort of RAM).
  >
  > But I just realized that they store COLOR frames!!!
  >
  > On computers, it takes a certain number of bit-planes to store any color at
  > all; e.g. 8 colors takes 3 bits per pixel; 256 colors takes 8 bits per pixel
 .
  > So the amount of RAM needed is greatly increased. I don't actually know how
  > many colors one can represent in color tv and how many bits that might
  > require.
  >
  > How much RAM is typically used for a frame? Is it a "half" frame or a full
  > frame? How many bits are used for the color representation, or is some other
  > means used than the typical computer x-bits per pixel method?
  >

 .Dave S. answers:
 .
 .The Amiga computer can display 4096 colors at once on the screen with less
 .than 0.5 meg.
 .
 .This memory is used for all processes and the program which displays the
 .pictures. (or creates them).
 .
 .The computer uses a Hold-And-Modify (HAM) method to do this.
 .
 .There are people in the news group "comp.sys.amiga" or
 ."comp.sys.amiga.tech" who know much more about this than I, so
 .they might be able to give you some very good answers to this question.

 I appreciate the help, but I am asking quite specifically about the
 technology used in consumer VCR's with digital special effects.
 That is, is it the case that a Toshiba or whatever "digital" vcr
 selling for $400 just happens to have half-a-megabyte of RAM to
 enable it to freeze a frame? Or do some of these machines have to have
 a meg or more to store and display one frame with one-half meg while
 saving up the next frame in another half-meg, to enable clean digital
 forward search?

 Whose chips are used, in what way?

 Another reader, whose name is not handy, was also curious. He was
 hoping that one could devise a way to extract from a consumer VCR
 the grabbed frames, and get them into his computer. Again, nobody seemed
 to understand the question, and offered all sorts of solutions that
 involved buying scanners and computers.

 The overlooked point we are both interested in is: frame grabbers are
 sitting right there in cheap VCR's, and some of us want to grab
 that technology rather than buy and use the much more expensive
 industrial stuff that does the same job.

 I am asking this now also in sci.electronics, since some of them may
 know more about the chips used.

 (a) how is this done, how many bits, how are they used to represent
 the equivalent of pixels, how is the color saved, what chips are used?

 (b) how might one conceivably grab a grabbed frame, by wiring into
 a consumer vcr?

 (                                                            )
 (          Doug Mosher <SPGDCM@CMSA.Berkeley.edu>            )
 ( 257 Evans, Univ. of California, Berkeley, CA, 415/642-5823 )
     +Re: frame buffers for digital vcr's