Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!mailrus!ames!elroy!gryphon!cadovax!keithd
From: keithd@cadovax.UUCP (Keith Doyle)
Newsgroups: comp.sys.amiga
Subject: Re: Digitizing
Message-ID: <2249@cadovax.UUCP>
Date: 13 Sep 88 19:46:46 GMT
References: <3413@crash.cts.com>
Reply-To: keithd@cadovax.UUCP (Keith Doyle)
Organization: Contel Business Systems, Torrance, CA
Lines: 41

In article <3413@crash.cts.com> mikeg@pro-charlotte.cts.com (Mike Gladden) writes:
>2) I also have a Digi-View and the necessary adapter for the Amiga 500.  I
>   don't have any problems with this setup, except that the used B/W camera
>   I have is just a piece of crap.  I've read that the average color video
>   camera doesn't have enough resolution to do the job as well as most B/W
>   cameras.  But the specifications on my new GE CG-9808 video camera seem
>   to indicate that it does have good enough resolution.  The scoop on the
>   camera section indicates:  Scanning - 525 Lines / 60 Fields / 30 Frames.

The problem with using a color camera for digtizing (or a VCR output for
that matter) is that standard NTSC color is achieved by adding a 3.58Mhz
phase modulated sine wave on top of the standard B&W (luminance) signal.
3.58Mhz can actually represent luminance information that is big enough
to see.  Most standard B&W tv's have a 3.58Mhz notch filter designed to
filter this signal out, so you don't see it on the screen.  If you've
evern looked at an old old tv that didn't have a notch filter, or one
that has had it disabled, you'll find you can actually see the graniness
produced by a visible 3.58Mhz signal.  On a color TV, this signal is
filtered out and used seperately for color information.

When you run a color signal into a video digitizer, one of two things are
going to happen:

1.  You are going to see undesirable herringbone effects due to digitizing
the 3.58Mhz color carrier as if it was part of the image.

or

2.  You are going to lose some of the high frequency components of the
image if the 3.58Mhz signal is filtered out.

Because of this, you will generally always be able to get a better
digitized image using a B&W camera with filters than if you use a
color camera or color signal from a VCR.  

The other difficulty may be that using color filters on a color camera
could give you incorrect color balancing, though I don't know for sure.
For a B&W image it's probably passable.

Keith Doyle
#  {ucbvax,decvax}!trwrb!cadovax!keithd  Contel Business Systems 213-323-8170