16 bit yet 0-255 in PS??

I didn't want to pose this question in the latest post asking about RAW, so I'll post separately. First, I shoot RAW (landscapes, 100%; I'm not in a hurry:)) and I fully understand the technology behind 16-bit processing as opposed to 8-bit JPEGs. My question is this: Is the 16-bit latitude only useful/available during the RAW conversion process? In other words, I've noticed (for years now) that my files are 16-bit once they are converted and I'm working in PS. However, levels and curves only show 0 to 255 levels or 8-bits in their adjustments. So with that in mind, is there any reason or advantage to maintain 16-bit PSD or TIFF files once they've been converted from RAW?

Thanks

I'm no PS pro but my understanding is that all adjustments should be made in 16 bit, and saved as a TIFF for print, to retain the most image data. This is loss-less. Once you convert to 8 bit for jpg you go to compression mode, and each time you open and close this image it reexamines the bits to save in a compact form. I've tested this and opened and closed jpgs many times and examined the file size and find very little difference. Anyway, I do a save with my RAW so I can re-adjust if necessary, but any version I am happy with I save in TIFF format. As for the PS adjustment question on 16 bit I guess Adobe figured that most purists will save as TIFF for print and to re-write the algorithms in 16bit across the board would need more memory (take longer to process) for each step along the path. I do at times convert back and forth 16/8 within PS on a single image to use the controls I need, end up at 16 bit as a final, saving/re-naming as a duplicate, & save as jpg. Then I do any resizing, etc.

Like I said -- I'm no PS pro but if anyone out there wants to clarify, I'm willing to learn.

And on a side note, I'm a Boise guy born and raised. My bones will be planted around Stanley.

And guess I didn't touch the 0-255 question. Not all images have a value of either 0 or 255. If you trust your monitor and like your image, leave it alone. Many portrait guys like myself use 240-245 as the top end of the highlights most of the time.

Bob - I think you missed the point. In 16 bit, you should technically see 0-65536, rather than 0-255. Aaron - I'd guess that's just an easy shorthand for the tools and not an absolute. The actual calculations on a 16-bit image are probably being made in 16-bits. I don't know for sure, but typically in PS tools that can't operate in 16-bit have been unavailable or warned you before processing.

David's right - it's really just a "failure" of Photoshop to not show a different tonal scale (i.e., 0-65536 instead of 0-255) when you have a 16-bit image open. Photoshop is NOT compressing those 65,536 tones down to 256 of them when 1 16-bit image is open.

Cheers

Brad

PS: Don't expect this issue to rise to the top of "things to address" in Photoshop CS6!

Bob,
You mention converting back-and-forth between 16 bits and 8 bits. My understanding ( possibly a misunderstanding ?) is that once an image has been converted from 16 bits to 8 bits it forever after carries only 8 bits of image data, even if converted back to a 16 bit file.
Any confirmations or denials out there amongst the PS cognoscenti?

Dave Graham
South Dakota

Hey Dave,

I don't qualify as a PS cognoscenti, but my understanding is that you CAN return the image to 16-bit, but because the extra data is simply "manufactured" (or created) from the existing 8-bit data, it just isn't worth doing (so lost tones are still lost). I can't guarantee I'm right...

Cheers...

Brad

Thank you all the feedback. That makes sense about only seeing 0-255 but actually working in a 16-bit space. And Bob, I recently lived in Boise for about 4 years and I think Stanley is easily the prettiest place in Idaho.

Brad - That's right. If you have 256 values in 8-bit, making it 16--bit still has the same original 256 values. Now in 16-bit you can shift them into any of the 65536 levels of 16-bit, but the starting point is the 8-bit levels.