Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!agate!pasteur!ames!coherent!dplatt
From: dplatt@coherent.com (Dave Platt)
Newsgroups: comp.graphics
Subject: Re: Film Recorders
Keywords: Output device, film, printer
Message-ID: <20660@coherent.com>
Date: 14 Feb 89 18:47:27 GMT
References: <1479@anuck.UUCP>
Reply-To: dplatt@coherent.com (Dave Platt)
Organization: Coherent Thought Inc., Palo Alto CA
Lines: 64

In article <1479@anuck.UUCP> g8@anuck.UUCP (k.d.tentarelli) writes:
> Can anyone answer some general questions on film recorders as
> graphical output devices?

I've recently been working a bit with Marc Kaufman, who wrote the Mac
"printer"-driver for the Mirus slidemaker.  Marc has been able to
"print" slides using the most recent version of my Mandelbrot-set
program.  We've had some discussions about the technology that Mirus
uses in their device, in the course of tuning the program.

> 1. Do they use CRT technology?

The Mirus uses a single monochrome CRT.  It "prints" in three passes, by
dropping red/green/blue filters between the camera and the CRT.

> 2. Does the resulting film show individual pixels, or do the pixels
>    scatter when being recorded such that the film looks continuous?

Yes. ;-}

The beam-spot on the Mirus CRT is somewhat larger than an individual
pixel.  The device's sweep-electronics handle a resolution of 1500 wide
by 1000 high (and I believe they'll slice even finer), but the
pixel-spots will overlap somewhat at this resolution.  In areas of
uniform color, the blend between pixels is quite seamless... I've
projected one of these slides, and the only graininess I could see was
due to the film itself (Ektachrome 100, I believe).  The driver-software
will dither areas of closely-related colors, thus providing a very
smooth blending.  There is none of the characteristic squarish
shadow-mask graininess that's observable on the AppleColor monitor (and
most other color monitors, I believe).

Things don't work so smoothly when pixels of contrasting colors lie
adjacent to one another, though.  If a red pixel adjacent to a green
pixel, there will be an area of yellow where the CRT spots overlap.
This is unfortunate, but appears to be inherent in the technology that
Mirus is using.  Mirus is aiming at the business-presentation market
rather than the scientific-visualization market, and have accepted
somewhat lower device resolution to help them keep the cost of the
equipment down.

Marc tells me that it's possible to see individual pixels even at the
device's highest resolution, but that the beam-overlap does cause color
artifacts.

> 3. How good is the color fidelity?  (I'm not sure of the best measure
>    to use for this.  Perhaps consitency of reproduction is a good
>    measure since any static color error could presumably be 
>    compensated for.)

I was very impressed.  Color balance appears to be an excellent match to
the AppleColor monitor I use at home.  Marc tells me that they use a
gamma-corrected color table.  The driver-software permits you to
identify the specific slide-film being used;  I suspect that the gammas
are tweaked in order to match the needs of individual films.

I think the color-matching used by the Mirus driver is distinctly
superior to that achieved by photographing the AppleColor monitor.

-- 
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