16-bit greyscale scans only record 8 bits

[Travis]

I just got my scanner and I'm trying to make 16-bit Greyscale scans. Unfortunately, the scanned image has all the information the lower 8-bits. I know this from viewing the histogram in Photoshop. This also makes the brightest white a midtone, so the first thing I have to do is adjust the levels. The image looks right in Silverfast before I scan it.

When I scan in color, this doesn't happen. But in greyscale, this happens regardless of the dpi or whether I'm scanning to a file or importing to Photoshop.

Also, I can only scan in HDR mode, because the normal 16- and 48-bit scans are greyed out in the selection menu. This is a bit odd, but I don't guess it matters.

What I can do to make a real 16-bit Greyscale scan?

[LSI_Morales]

Dear Travis

Unfortunately, the scanned image has all the information the lower 8-bits. I know this from viewing the histogram in Photoshop. This also makes the brightest white a midtone, so the first thing I have to do is adjust the levels. The image looks right in Silverfast before I scan it.

The histogram in photoshop is not a 16 bit histogram, as a matter of fact it can only show you an 8 bit image with 8 bit histogram. When you scan in HDR mode (either greyscale or color) SilverFast creates an unmodified raw file with a gamma value of 1 which means that the picture will look darker, however, the file contains more information which can not be displayed by the monitor, not by the histogram, in that case you have to apply gamma correction in your favorite editing program.

Also, I can only scan in HDR mode, because the normal 16- and 48-bit scans are greyed out in the selection menu. This is a bit odd, but I don't guess it matters.

Probably it is because you are using SilverFast SE or SE Plus. The normal 16bit greyscale or 48 bit color (no HDR) options are available in SilverFast Ai and Ai Studio.

Cheers

[Travis]

Photoshop will open files with 8, 16, or 32 bits per channel (http://livedocs.adobe.com/en_US/Photosh ... -78e8.html). Levels works in all of these modes, and even if it only uses 8 bits, the histogram would be showing that the image only uses the bottom 4 bits, which would be even worse.

The images I scan need level correction, not gamma correction. I created a screenshot to show you what I mean. There is no information in the upper half (and then some):
http://img266.imageshack.us/img266/204/histogram.png

Also, I was mistaken about scanning in color. Color scans have the same problem.

Since I feel sure Photoshop is really using 16 bits and gamma isn't the problem, there must be some other problem. Yes?

[LSI_Morales]

Dear Travis,

The images I scan need level correction, not gamma correction.

When you apply level correction you are actually modifying the gamma.

Are you scanning paper copies or original transparencies?

Thanks

[Travis]

I am scanning film negatives using a Plustek 7600i and Silverfast SE.

When I adjust the levels, I'm adjusting the black and white points. The gamma (the middle slider in Levels) says linear. The middle number stays at 1.00 when you move the left and right sliders.

But all that aside, right after scanning a frame, do normal histograms look like that? Or more specifically, am I supposed to see that histogram and think it is normal?

[degrub]

Just a shot in the dark - try deleting the Silverfast preferences files and make a scan. i've seen that cure some strange behavior before.

If that doesn't change things, what does the Silverfast histogram show ?

[LSI_Morales]

Dear Travis,

If you are scanning transparencies, the histogram should contain more information. You might want to try degrub's tip to see if this improves the situation.

Cheers

[Travis]

Well, I got rid of the preferences in "~/Library/Preferences/Lasersoft Imaging/SilverFast/Prefs/". Unfortunately, that didn't help.

However, I found a check box that moves the information to the middle of the address space instead of the lower bits. But, it's still only using about 8-bits of the space. The box is called "for HDR output" under General > Options > Gamma-Gradation. The difference can be seen here:
http://img801.imageshack.us/img801/1412 ... output.jpg

Also, I made a comparison between color and B/W. The color scans get about 12 out of 16 bits. But when you desaturate color in photoshop, it uses only about 8 bits and looks like the B/W scan. I don't really know why this is, but if it's done in Photoshop, I know it doesn't have anything to do with the scanner.
Here's a screenshot comparing B/W, color, and desaturated color:
http://img688.imageshack.us/img688/15/scancolors.jpg

Still, I should expect to get just about all 16 bits shouldn't I?

[LSI_Morales]

Dear Travis

However, I found a check box that moves the information to the middle of the address space instead of the lower bits. But, it's still only using about 8-bits of the space. The box is called "for HDR output" under General > Options > Gamma-Gradation. The difference can be seen here:

As a matter of fact what that box does is it applies the gamma value you have in SilverFast for other types of images (let say 2.0 or 2.2) to the 16 bit raw file.

Also, I made a comparison between color and B/W. The color scans get about 12 out of 16 bits. But when you desaturate color in photoshop, it uses only about 8 bits and looks like the B/W scan. I don't really know why this is, but if it's done in Photoshop, I know it doesn't have anything to do with the scanner.
Here's a screenshot comparing B/W, color, and desaturated color:

Exactly that is something happening within photoshop and is not relevant to SilverFast.

by the way, the link you have provided is not working.

Still, I should expect to get just about all 16 bits shouldn't I?

As a matter of fact you are getting a 16 bit file, Most likely your originals do not have much more information, remember that obtaining more information into the 16 bots does not only depends on the scanner or SilverFast but also on your originals.