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High Bit Scanning?

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Old 08-08-2001, 11:37 AM
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High Bit Scanning?

By Ed Ladendorf on Sunday, July 29, 2001 - 06:59 am:

Katrin Eismann explains the benefits of scanning in 16 bits per channel, but since photographs have limited information, compared to film, I was wondering if there was really a benefit from scanning in high bit when scanning photos. I asked this question on a scan mail list, and the answers I got (two) suggested that there is no benefit at all. After scanning a photo in 8 bit, then again in 16 bit, I made several tonal corrections. The resulting histograms were identical. But since her book is on restoration, it seems logical that she was probably talking about scanning photos rather than film. Does anyone here have an opinion on this? Doug? Anyone?


By thomasgeorge on Sunday, July 29, 2001 - 08:18 am:

Ed, I do almost all my work in 8 bit mode. On the occasions I have scanned at 16 bit I really didnt notice too much improvement. That is not to say that there are not benifits to scanning at 16 bit however I suspect that the type of work (art vs photo) may also play a role. On the occasions I do use 16 bit data I do most if not all my processing in Picture Window which allows you to do quite a bit more with the 16 bit images than Photoshop does. Good luck, Tom

By Doug Nelson on Sunday, July 29, 2001 - 10:42 am:

The advantage to scanning in 16bit mode is that there is too much information. Initially, more than you need or could see in printing. However, many of the most common operations are lossy, and that's where that 'excess' information comes in handy.

Scan a photo in at 8 bit, and then at 16 bit. Use levels on them both to remove the 'tails' of noise, then convert the 16bit to 8 and compare the histograms of the two.

The 8bit will show a 'comb' pattern, representing data that was lost in between tones. The 16bit will look solid and very much like that of an 8bit image before levels adjustment.

Normally I scan in 16bit and do all operations that are possible while in 16bit mode (many are disabled). Only then do I drop down to 8 to finish up.

Also, there is no advantage to converting an 8bit image to 16. If the information isn't there it's just interpolated, which takes control out of your hands.

By Ed Ladendorf on Sunday, July 29, 2001 - 12:59 pm:

Thanks for the reply. I need to get things straight in my head (which is seldom on straight ).

Thanks also for your reply. I do however, need one thing clarified. If you scan a photographic print at 16 bits per channel, but there really isn't that much information available on a print, isn't that a little like scanning in 8 bit, then converting to 16 bit? Or is the 16 bit scan actually picking up more useable information than the 8 bit?


By Doug Nelson on Sunday, July 29, 2001 - 03:34 pm:

Regardless of how it looks to you, the information on an original print is still continuous. It will always be more accurate than interpolation

By Ed Ladendorf on Sunday, July 29, 2001 - 04:07 pm:

Got it! Thanks
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Old 08-18-2001, 02:06 PM
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Silly Me!

I just discovered that you can choose to work either in 8 bit or 16 bit mode in PShop :p Wow there is so much to learn. Just to be curious--what pertinent features are turned off in 16 bit mode? I suppose I could find out for myself but just thought I'd ask while I'm here.

Also, I've got a HP scanner with a bit depth of 36. Since they don't trust me to change the bit settings (all I can change is resolution) is it safe to assume that all scans are scanned using 36 bits and then PShop converts them automatically to the 16 bits that it can handle?

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