From: daver@felix.filenet.com (Dave Richards)
Newsgroups: rec.video
Subject: Re: Coming out of the closet...
Date: 1 Sep 92 03:08:20 GMT
Reply-To: daver@fritz.filenet.com (Dave Richards)
Distribution: usa
Organization: Costa Mesa, CA

In article <1992Aug26.160955.18906@kong.gsfc.nasa.gov> jonke@kong.gsfc.nasa.gov (Stephen Jonke) writes:
>> Not really.  A 16:9 ratio is not wide enough for any of the wider films
>> like Blade Runner that are 2.35:1 (you still lose about 1/3 of the picture.)

I hate to make a pest of myself, but the 35mm anamorphic aspect ratio is not
2.35:1.  It's 2.39:1 (I round it to 2.4, but most people seem to love the
two-decimal-place accuracy.)  It has been 2.39:1 for the last 21 years, or
since 1971.  I'll keep bringing this up until people either a) start using
the right number, or b) stop quoting ANY specific value and just say "scope"
or "anamorphic."

>Incidentally, 16:9 is the same as 1.77:1. So for a 1.85:1 ratio film,
>you're only losing about 4% of the image.  Obviously this is not a big deal,
>but I'm a purist and there's no way you can truly get the full width even
>if your TV does not overscan at all (unless letterboxing is still employed.)

I have never heard of a film that was shot with a hard matte at 1.85:1.
Granted, many DPs don't protect the full Academy frame for TV, but even
the laziest ones protect a height of 1.75:1, and most are protected to
1.66:1.  I have no doubt that with a 1.85 film on a widescreen set we will
see the full width of the 35mm frame.  It remains to be seen whether the
software will typically have a slight (2%) crop at the top and bottom, or
if the frame will simply be opened up a little from the theatrical.  Either
way, I won't care because I don't think the difference will be apparent. (by
the way, most 1.85 films that are available now "letterboxed" are not mat-
ted at 1.85.  They are typically 1.5 to 1.7.  So you could use this same
software on your widescreen set and the screen would be completely filled.
You would be missing nothing.)

>The question I have is why did they not choose 1.85:1 as the ratio for HDTV?
>Then, 2.35:1 films have a relatively mild letterbox, 1.85:1 transfers exactly
>and Academy ratio films and NTSC TV broadcasts have reasonable side boxing
>(for lack of a better name!) Because of the latter, making HDTV 2.35:1 would
>be a mistake.

There's an article by Russ McMurtray in the latest "The Perfect Vision" about
the choice of aspect ratio for HDTV.  It helps explain this, although the
method given for the selection of 16:9 is off a little bit. (It claims that
the 1.7777 value was chosen because it's midway between the U.S. 1.85:1 stan-
dard and the European 1.66:1 standard.  That's simply not true, although it's
close.)

As it was explained to me, the number was selected as follows:
The image sources that are likely to appear on HDTV have aspect ratios ranging
from 1.33:1 (present TV and old silent films) to 2.39:1 (the widest common as-
pect ratio for films.  There ARE wider ratios, but they've been so rarely used
they aren't worth considering).  If you superimpose rectangles of those two
extreme ratios, each having THE SAME AREA, the area that is common to both im-
ages is a 1.78:1 aspect ratio.  This means that both 1.33 and 2.39 images would
lose about the same amount of picture area if cropped to 1.78:1.  Or if the
images were letterboxed/widowboxed, in both cases the unused screen area would
be about the same.  Note that comparing areas in this way is NOT the same as
taking the average of the two ratios, which gives about 1.84:1.  

This is shown graphically below:

                         1.33 outline
	    ,-----------------------------------,
	 ___|___________________________________|___
	|   |                                   |   |
	|   |                                   |   |
	|   |                                   |   |
	|   |          1.78 common area         |   | 2.39 outline
	|   |                                   |   |
	|   |                                   |   |
	|   |                                   |   |
	|___|___________________________________|___|
	    |                                   |
	    '-----------------------------------'

If both images are 1 square unit in area, the dimensions are as follows:

	Ratio	Width	Height
	1.33	1.155	.866
	2.39	1.548	.646

I personally would have preferred that a ratio was chosen that was already a
film standard, such as 1.66 or 1.75.  Those are also represented by smaller
fractions which are easier to remember.  But that's water under the bridge.

Dave
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