RE: 16 bit editing...

[Michael Greer <mgreer316@yahoo.com>]

Gus,

I know and understanding all of the theory behind why using 16 bit images is
preferable to using 8 bits images. Like I wrote initially, mentality, it makes
perfect sense to me. But read what I wrote, nobody has yet produced a side by
side comparison that I've seen of an image that actually reveals the issues
with using 8 bit images. I just haven't seen it. That's not to say I don't
believe it isn't possible. But why after all these years has a simple 16 bit
vs. 8 bit side by side comparison of the same image undergoing the same editing
functions been produced so that the diferences can be seen? Why all of the
theory explanantion when a simple side by side display on the web would do the
trick? I read a lot of people rehashing the same theory, but still no
comparisons. And believe me, I've tried! I've taken real 16 bit images and
preserved them at 16 bits in an editing session. I've taken that same image,
bumped it down to 8 bits, then edited it with the same editing steps. The
result? No difference. I've done this with several different images at
different points in time over the years. 

I remain ready to be convinced. Maybe it only reveals its superiority with
certain types of images. I don't know. But it's a heck of a penalty to pay when
the advantages are apparantly so hard to come by.

--- Gus J Grubba <gus@grubba.com> wrote:
> 
> 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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=====
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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