What are the advantages of 48-bit color scanning?

[Editor www.nutritionsoftware.org]

When I use PhotoShop 6 and can only edit using 24-bit color? (Am I wrong
about this?)
Shouldn't I just scan in 24-bit mode to save time and space?

I just got an Epson 3200 scanner which is capable of 48-bit color mode. If I
use Silverfast, I see a scan mode listed as "48->24 bit color". Does this
mean the scanner uses 48-bit mode but the software converts to 24-bit for
output?

When I use Epson Scan, the 48- and 24-bit modes are listed separatedly. If I
use the 48-bit mode, I can see the file in Photoshop but cannot copy and
paste, etc.

Thanks for any enlightenment. A few years ago I had some bad experience with
scanning, but am giving it another try. Scanners are getting so much better
and cheaper these days.

--
Editor, Internet's Convenient and Unbiased Directory of Nutrition Software
[url]http://nutritionsoftware.org[/url]

[Leonard Evens]

Editor [url]www.nutritionsoftware.org[/url] wrote:

> When I use PhotoShop 6 and can only edit using 24-bit color? (Am I wrong
> about this?)

I think you are. I have Photoshop 6, and I'm pretty sure I can edit in
48 bit color, at least for the most common operations. I don't use
Photoshop very often, so I would have to check. But there are certainly
some operations I perform fairly regularly which can only be done in 24
bit color depth in Photoshop. Photoshop 7 does more in 48 bit, but not
everything.

> Shouldn't I just scan in 24-bit mode to save time and space?

In prinicple you should do as many editing operations in 48 bit color
depth as you can, particular operations which spread values. The reason
is that you start with a certain number of distinct possible values, 256
for 24 bit and 65536 for 48 bit. Some operations, such as expanding
contrast will cut down the size of the range and spread the values
apart. You can see this often as gaps in the histogram. If the
changes are not too large, your eye can't detect them, but it is still a
good idea to avoid too large gaps. With 65336 values you have much more
room to work without producing any noticeable effect. So you should
probably scan in 48 bit color depth and do as many operations as you can
in 48 color depth. Before printing or archiving the result, it is
probably okay to switch to 24 bit. Also, some of the operations you
want to do in Photoshop may have to be done in 24 bit, but you can save
those for last.

>
> I just got an Epson 3200 scanner which is capable of 48-bit color mode. If I
> use Silverfast, I see a scan mode listed as "48->24 bit color". Does this
> mean the scanner uses 48-bit mode but the software converts to 24-bit for
> output?

Yes.

>
> When I use Epson Scan, the 48- and 24-bit modes are listed separatedly. If I
> use the 48-bit mode, I can see the file in Photoshop but cannot copy and
> paste, etc.

???

>
> Thanks for any enlightenment. A few years ago I had some bad experience with
> scanning, but am giving it another try. Scanners are getting so much better
> and cheaper these days.

I use Vuescan to scan, but I edit in the Gimp under Linux, which does
only 24 bit color depth. I scan in Vuescan at 48 bit depth, do some
preliminary operations such as choosing black and white points, and
making an initial choice for gamma, all in Vuescan, and I save in 24 bit
depth. I do my remaining editing in the Gimp. So far it seems to
work fine. I don't detect any degradation of the image.

>

[Rafe B.]

On Wed, 16 Jul 2003 16:54:51 GMT, "Editor www.nutritionsoftware.org"
<nseditor2002 [email]REMOV@hotmail.com[/email]> wrote:

>When I use PhotoShop 6 and can only edit using 24-bit color? (Am I wrong
>about this?)
>Shouldn't I just scan in 24-bit mode to save time and space?

Scanning in 48-bit (16 bits per color) is popular but IMHO
wasteful. Some people consider it "key" to getting good
color, and that's hogwash.

Do a google search on Dan Marguls for some expert
opinion on this ([url]www.ledet.com\margulis[/url]).

What 48-bit does do for you is it allows you to carry some
sloppiness up the signal-processing chain before critical
image data is irretrievably lost. I would argue that that's
a poor reason to use it.

However, if you take reasonable care with your scans
in the first place, and reasonable care afterward in your
image editor (with regard to tonal manipulatin) there is
little or no advantage to scanning in 48-bit.


rafe b.
[url]http://www.terrapinphoto.com[/url]

[Bart van der Wolf]

"Rafe B." <rafeb@adelphia.net> wrote in message
news:9iqbhvg1jb3onsqktjjib5m3utfb0iueca@4ax.com...
SNIP

> Scanning in 48-bit (16 bits per color) is popular but IMHO
> wasteful. Some people consider it "key" to getting good
> color, and that's hogwash.

Assuming you mean scanning in 48-bit and not output in 48-bit, I have to
disagree. Scanning in 48-bits allows to do inevitable gamma correction
without causing posterization.
Whether 48-bit output after the major tonal corrections is wasteful, depends
on the capabilities of the scanner software. Not all software e.g. allows to
apply Curves corrections / Histogram Equalizations, so they need to be
applied afterwards.
Should significant additional correction be needed, 48-bits is unavoidable.
If you don't need to adjust the file, 24-bits is probably fine in 90% of the
cases, although I prefer to do things like sharpening and noise suppression
in a 16-bit Luminance channel.

So to make a long story short: It depends.

Bart