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I'm watching a Lynda.com course named "Scanning Techniques for Photography, Art, and Design" (https://www.lynda.com/Design-Digital-Illustration-tutorials/Scanning-Techniques-for-Photography-Art-and-Design/84091-2.html). In it, the presenter repeatedly mentions the benefits of using a higher bit depth (such as 16-bit grayscale, or 48-bit color), but then chooses a scan option which itself reduces the bit depth (such as 16-bit to 8-bit grayscale).

Although he does explain why one would scan at a higher bit depth, he does not explain why one would scan at a higher bit depth but then convert to a lower bit depth, so I'm wondering under what circumstances someone would do that. I've thought of two options:

  • Space: more bit-depth = more bits = more space taken up by an individual scan. But since I have plenty of space, this isn't really a concern for me
  • Processing speed: more bit-depth = more bits = more bits to process when trying to manipulate the image. However, more bits (generally) means more information, and therefore you'd get a better result at the cost of that increased time spent processing. That makes the argument for deciding between 16-bit or 8-bit, but not for why someone would use a "16->8 Bit" option.
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Scanning at high bit depth and reducing it for saving has similarities with shooting raw and converting to an 8 bit per channel format. You can optimise the dynamic range (in the typical scanner options, brightness and contrast) using software on a PC after collecting all the data. A PC can easily handle non-linear mapping of 16 onto 8 bits unlike the simple microcontroller firmware).

  • This was my thought process. I do save my RAW images too, though - I only convert to JPG because most tools or online services use JPG's. In the case of scanning, converting a 16-bit JPG to an 8-bit JPG is only for storage. I just wanted to find out if there were other reasons as well - thanks! – Jake Jun 2 '16 at 18:39
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    @Jake the 16 bit format is more likely to be tiff with some form of lossless compression applied. I don't keep all my raws but always shoot raw+jpeg. – Chris H Jun 2 '16 at 19:15
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a higher bit depth but then convert to a lower bit depth

Because sometimes some device simply won't display a 16 bit image.

Chris H already mentioned. The reason to scann it at higher bit depth is because you want a flexible digital original.

What's the point of capturing 14 bit images and editing on 8 bit monitors?

If you just want an out of the box scann yea, you can simply scann at normal 24 bits.

At the end a 8 bit per channel image is considered an "output" or final image: for a werbpage, pre-press, the file that you use for a print.

A higher depth per channel is a "working" file for editing.

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