8-bit vs. 16-bit

[ddt0725]

Hi guys -

I have a few questions regarding the above named title. I have searched online but everything I find tends to give me more information than I really am looking for ...too much overload on my tiny pea brain!

When I bring photos into Photoshop, they are set at 16-bit. Some of the actions I have require the photo to be in 8-bit for them to run. So, if I change my photo to 8-bit to use that action, should I leave it set to 8-bit to say run other actions that would also run in 16-bit or if I want to apply any textures? Does it change or degrade the thus far edited image any if I move it back to being set at 16-bit. Or, even if that is the only action I run and I'm done ...should I save and/or print the photo in 8-bit or move it back to 16-bit ...or does it make any difference. On my screen, I don't see any difference at all. If I am going to print the photo, would it be better to not use actions that require switching to 8-bit?

Any input would be appreciated! Thanks!

Denise

[neuroanatomist]

Current Canon RAW files are 14-bit (luminance of each pixel has 2^14 possible values), so a 16-bit file retains all of the data. When you reduce to 8-bit, you are basically throwing away the extra 6-bits...you can't get them back (like setting the mode to grayscale permanently removes the color data).

You won't see a difference on your monitor, since all but the uber-expensive ones (e.g. Eizo) are limited to 8-bits (or less for some cheaper LCD panels). Printing has similar limitations, particularly since most commercial printers want JPGs which are 8-bit.

To the extent possible, I'd say do all the operations you can in 16-bit space before reducing to an 8-bit file.

[ddt0725]

Thanks, John ...that exactly what I needed to know! Much appreciated!

[DavidEccleston]

John covered almost everything, except for when the bits are useful (aside from Marketing ). The extra bits only real function is that they can help keep a gradient smooth after you perform a change to contrast or apply a curve (for photos, think of skies for large slow changing gradients). For digital painting, overlapping dabs of very-large soft-edged brushes can also show banding and off-color blending artifacts, but you're not likely to use the offending combinations very often.

Elements doesn't even have 16-bit mode, so after RAW conversion, I'm working in 8 bit mode, and it's not really a problem.

[ddt0725]

Thank you for the info, David. I wasn't going to post the question but I am glad I did. The information provided has helped a lot. You guys still teach me something every time I log on here!