Re: Off Topic: PhotoShop6 16 bit. PS6 16 bit tif.lzw rotate and save size growing problems
Re: Off Topic: PhotoShop6 16 bit. PS6 16 bit tif.lzw rotate and save size growing problems
- Subject: Re: Off Topic: PhotoShop6 16 bit. PS6 16 bit tif.lzw rotate and save size growing problems
- From: "Thomas Knoll" <email@hidden>
- Date: Tue, 15 May 2001 14:11:10 -0700
]Now I'm wondering about a couple of other options that don't work as
expected in PSv6 with 16 bit files. I've tried tech support with no luck. I
have just sent copies of the basic problem 16bit files to tech support via
email.
Problem: 16 bit files rotated via the canvas or the crop tool grow 20% or
more when saved as Tif with LZW compression! It appears to only affect an
arbitrary few degree rotation, not a full 90 or 180 rotation.
Maybe folks on this list could verify or shed more light on this one as I'm
sure we're all very excited about the new options available for editing
16bit files in v6. Here's our dilema, and the answer we get from tech
support is "why are you doing that with such a big file anyway?". The
problems cost us countless hours working on a 16bit raw drum scan that was
645 MB as 16bit just small enough to fit on a CD for archiving and
transport. Opening and resaving and resaving again, arrgh! As it turns out
we have the problem repeatable on much smaller 16bit files that we could
have been testing the issues on but we wer'nt aware of it to this noticable
extreme. I was asked to send off the 600+ MB file via email (They won't
accept a CD in the mail), however since we have discovered a problem with
smaller sized files we are sending off 100MB versions.
The original file is probably not a true 16-bit per pixel file.
Instead it is more likely a 12 or 14 bit per channel file padded to
16 bits (actually 15.001 bits in Photoshop). When you rotate by a
non-90 degree angle, Photoshop interpolates values between pixels.
The result is an image that uses all of the available bits per
channel. This file then compress less well than the non-rotated file
using it looks to the compressor like it has more bits.
Thomas Knoll