What are the advantages of 48-bit color scanning?

NR
Posted By
nseditor2002 REMOV
Jul 16, 2003
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387
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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 http://nutritionsoftware.org

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Leonard Evens
Jul 16, 2003
Editor www.nutritionsoftware.org 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.

R
rafeb
Jul 17, 2003
On Wed, 16 Jul 2003 16:54:51 GMT, "Editor www.nutritionsoftware.org" <nseditor2002 > 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 (www.ledet.com\margulis).

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.
http://www.terrapinphoto.com
BV
Bart van der Wolf
Jul 17, 2003
"Rafe B." wrote in message
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

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