8-bit grayscale for black & white photographs

[Edalongthepacific]

Is there any image detail lost in a black and white photograph if it is converted from 16 -bit Adobe RGB to 8-bit grayscale?

[Schewe]

Image "detail"? No (other than going from RGB to Grayscale) but in terms of levels, yes, about 32,513 potential tone levels.

Note, Photoshop's "16 bit" is actually 15 bits plus 1 level for a potential range of 0-32,768 or 32,769 levels...so, 32,769 minus 256 levels (8 bits) would be 32,513 less levels in the 8 bit version.

[Edalongthepacific]

Thank you. Assuming all tones were as desired at 16-bit RGB would there be a loss of existing tonal values (as opposed to potential tonal values)  when converting to 8-bit grayscale.

[Schewe]

Well, you would be mode changing from 16 > 8 bits...so there would be a loss of levels but for most purposes that shouldn't be visible. If you then did any other tone adjustments or transforms there would be further loss of levels that would further reduce the 256 levels of the 8 bit image that might end up being visible in the form of banding or posterization. Note, sending the 8 bit image to a printer could also reduce the 256 levels...

Is there a reason you want to go from 16 bit RGB to 8 bit grayscale instead of 16 bit grayscale?

[Edalongthepacific]

I guess I hadn't thought of 16-bit grayscale. I thought grayscale was 8-bit by definition (my bad). I am interested in efficiently sending B&W images over the internet...so its a bandwidth issue more than anything else.

[Schewe]

As long as the 8 bit image has no further processing, I doubt it'll be a real issue...so if the 8 bit image is for viewing only, 8 bit would be fine.