Found an old copy of Photoshop CS (version 10) on a very old Mac.
I still have every copy of Photoshop on my Mac :-p https://www.on-sight.com/30-years-of-photoshop-and-counting/ <https://www.on-sight.com/30-years-of-photoshop-and-counting/> Sadly I didn’t keep the pre 1.0 versions….
Converted my grayscale doc using your settings from Gray Gamma 2.2 to Adobe RGB (1998). Results are the same: 0/21/25/28/33. The same results I get in Photoshop CC 2022 and Lightroom Classic. Nothing wrong here, sorry.
As I said that’s my finding as well. But that doesn’t help Peter, nor solve why he’s experiencing what he’s experiencing. I believe his confusion is common and relates to how Photoshop calculates color back and forth between these modes based on his Color Settings. I think he probably created the grayscale file with sRGB numbers and is then surprised when they change to AdobeRGB numbers… His new install is probably defaulting to sRGB as the working space... Scott Martin www.on-sight.com Imaging Science for Art