GIMP Version: 2.10.32
Operating System: Linux
OS Version: Ubuntu 22.04
GIMP Experience: Experienced User

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I am still trying to get my head around 16-bit grayscale mode.

Section 6.5 of the 2.10 documentation reads in part:
* A 16-bit integer grayscale image provides 65535 available tonal steps from 0 (black) to 65535 (white).
but the phrase "tonal steps" does not appear to be in the glossary.

It seems reasonable to interpret this as meaning that there are 65534 other "available tonal steps" which I presume increase uniformly from 1 to 65434 although that is not stated explicitly.

My question is simply this:
Q. If there are "65535 available tonal steps" in 16-bit grayscale projects, how may I "avail" myself of them?

If I cannot access them, I simply cannot understand how they are "available."

Thank you for tolerating my thickness-ness/obsessing.

Another interesting question.
I think you can equate tonal steps with unique colors. I remember from some time back the Gimp devs saying the color-cube analysis is only good for 8 bit.

You can get a measure using Imagemagick on an exported image


As a screenshot, comparing 8 bit and 16 bit gradients with the results



As you might expect, 8 bit is 256, while16 bit not quite your 6535. I got 54631 There are three different color spaces for gradients, slightly different values but much the same. This one Linear

"increase uniformly": depends what "increase" refers to: if the plain numbers, then yes, but if the luminosity, only if you are in linear light mode.

@Ofnuts, okay, that's what I meant. :^) Linear light is what I want.

@rich2005, I've been misleading myself by using blind-to-all-but-8-bit "Colors->Info->ColorcubeAnalysis" to "check" how many graylevels are in my 16-bit gradient and convincing myself it wasn't really 16-bit.

But... I don't get a lot of reassurance when I use the "Color Picker" to set a foreground/background color; it seems to report something between 0.0 and 100.0 (in my case with 1 dec. pt. precision, implying 1,000 colors).

Now what I haven't checked... is IF I can set a colors like, say, 012345 and FEDCBA hex as foreground and background colors, run a linear CIE gradient and see what kinds of values Color Picker shows near the endpoints.

And so I checked. Both 012345 and FEDCBA appear are shades of blue when selected as foreground and background colors, but using them with the Gradient tool (blend:CIE shape:linear) produces something that has only 256-levels of gray: sampling anywhere in the result produces a color in RRGGBB format with RR=GG=BB--256 levels.

So while I can then access ANY "color" from 000000 to FFFFFF, they do not map to 65536 (actually) levels of gray.

AND NOW, it dawns on me like a falling load of bricks what Ofnuts has been repeating: 65536 "unique" colors when converted to still only map to 256 unique levels of gray.

I found this example on stackexchange which I would not have gotten from the wikipedia article on CIELAB/L*a*b color space.



(I'm almost done. There remains one question.)

The one question remaining is:

Is there a tool that does permit working with 16-bit-level grays in a similar fashion to GIMP's approach of painting layers and combining them by stacking them and applying different modes?

Is such functionality contemplated for GIMP3?

Is it--shudder--available in PS?

Thank you all for your help and patience. "By Jove, I think I've got it!"

Since most systems really cannot display 64K scales of gray (not to mention, the eye cannot even perceive even close to those shades), another approach would be to use pseudo-grey. You stick with 8 bits and get quite good results. Posted the thread below a few years back; surprised the justpasteit link still works (even though I no longer can even edit that link; lost the log in code due to bit rot; lol).

viewtopic.php?f=23&t=4245&hilit=pseudogrey