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Subject: Re: [AE] Quick AE Render question.
From: Chris Zwar <chris@chriszwar.com>
In-Reply-To: <list-5266861@media-motion.tv>
Date: Tue, 29 Oct 2013 07:34:19 +1100
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Message-Id: <2DAE7279-EE02-4FC6-84E8-71AB8F367F57@chriszwar.com>
References: <list-5266861@media-motion.tv>
To: "After Effects Mail List" <AE-List@media-motion.tv>

On 28/10/2013, at 11:41 PM, Robert Kjettrup <robert@stvmayday.dk> wrote:
>=20
> Thanks Chris for the tip about NOT using LZW compression on 16bit tiff =
files. Never thought about that could be a problem, i always leave this =
setting on. But dosent this more sound like a bug?

It's not a bug, it's just the way the algorithm was designed.  LZW is a =
very old and primitive form of compression and was specifically designed =
for 8 bit files.  It looks for patterns or values that repeat themselves =
a lot, and builds up a table of these repeated values.  In an 8 bit file =
where each value is restricted to 0 - 255 there's a high probability =
that sequences of numbers will repeat themselves, especially for things =
that have an underlying structure like language.  LZW can still do very =
well on text files, for such an old algorithm.  But in a 16 bit file the =
range of values is so much bigger (0-65535) that the probability of =
having specific sets of numbers that repeat falls dramatically, and the =
table becomes an overhead.

I imagine that for simple images, such as mattes, then LZW would still =
offer impressive file size advantages in 16 bit mode.  But for natural =
images such as photographs then it just doesn't work very well, and it's =
due to the 8 bit nature of the algorithm's origins.

I suppose it's a case of YMMV, but in general LZW isn't recommended for =
16 bit tiffs.

-Chris=