RE: 16 bit editing...

["Gus J Grubba" <gus@grubba.com>]

The difference comes when processing an image. When you change levels,
curves, or other operation that alter the "gamma" of an image, you are
altering the steps between the values. If you only have 8 bits, you have
256 steps to play with. Some of these steps are going to get really
steep. When using 16 bit images, you have a lot more information to work
with and these steps are then smoother. Imagine an image where you only
have three tonal values. All white, middle gray, and all black. If you
want to bring the middle gray closer to the white, the difference
between gray and black gets steeper. The more values you have to begin
with, the smoother the "curve". Note that this is the case when you
start with 16 bit values. You can convert an 8 bit image to 16 in order
to "smooth" out a curve but that is not quite the same.

People tend to think of it as amount of information available to print.
No, the printer cannot directly deal with 16 bit values. But... it will
be a lot better image if you start with a 16 bit image and process the
RGB -> CMYK conversion within that realm (most Ink Jet printers are
strictly CMYK printers even though natively, both Mac and PC only
understand RGB color space).

In my opinion, serious work can only be performed within 16 bits. It
amazes me that Photoshop, after all these years is still so restricted
in this regard.

The easiest way to test this is to start with a long ramp. Change the
curve and watch the resulting image and histogram. Do the same with a 16
bit image. Ideally you will need a tool to create a true 16 bit ramp as
Photoshop's ramp tool does not work with 16 bit images.




-----Original Message-----
From: owner-epson-inkjet@leben.com [mailto:owner-epson-inkjet@leben.com]
On Behalf Of Michael Greer
Sent: Tuesday, May 21, 2002 4:24 AM
To: epson-inkjet@leben.com
Subject: Re: 16 bit editing...


Dave,

Many times I preserve my images in 16 bits throughout my editing
sessions
because the theory of using 16 bits in editing sessions makes sense to
my
rational mind. But I gotta tell you, I have yet to actually see these
differences in real pictures. MANY are very passionate about editing in
16
bits. They give you the reasoning. They present charts and graphs. They
give
you test cases (like color bands), instruct you to perform various
editing
functions, then tell you to evaluate the histogram to see the
differences. But
in all my years of doing this, I have yet to have 1 person present 2
real
pictures, one edited in 8 bits, the other in 16 bits, that actually
reveals the
difference. It's not just me either. Dan Margulis, author of
Professional
Photoshop apparently has a standing bet. From what I've heard, he's
challenged
anybody to produce an image that reveals the difference in the image,
not in
charts or graphs. From my understanding, nobody has done it yet.

I stand ready to be convinced because the reasons to edit in 16 bits do
make
sense to me. So much so that I do edit in 16 bits many times for "just
in case"
reasons. But until I acutally see an example of the difference, I'll
never be
fully convinced that it matters.

> 
> 
> Bob,
> 
> Just wanted to ask a few questions regarding 16-bit editing.  Are you
> working in B&W or color (maybe both)?  I've read that the main benefit
of
> 16-bit editing is in the preservation of shadow detail, but it sounds
like
> you apply it to most if not all of your images.  The dumb question to
ask
> would be "Do you really see a big difference?" but obviously you do or
you
> wouldn't make the effort.  So instead I'll just ask if you could maybe
make
> a few comments describing images in which you've compared 16-bit and
8-bit
> editing (perhaps from your original testing?)
> 
> I haven't tried it yet with my color work in that I tend to work with
large
> files (300 meg scans that can get very big, very fast), and I'm afraid
that
> going to 16-bit might clog my Mac a bit.  Your comments will be
> appreciated...
> 
> Dave Schrader
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 


=====
Visit my digital photography web site along with a lot of other
interesting stuff at http://www.mikegreer.com. Also, Greer and
Associates (http://www.greeraa.com) offers studio photography, digital
imaging services, web site design/construction, and training. 

Mike Greer

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