Adjusting Value

[Espermaschine]

I have a grayscale layer for a Displacement Map. Its basically neutral gray, but there are other bits in various grayscales.
Because of processing, the basic gray changed and is no longer neutral gray.

How do i adjust it so that its exactly 50% gray again (808080) ?

When i use something like Levels or Curves, the tool doesnt tell me when im at my desired value.

There must be another way than just eyeing it.

   

[rich2005]

Maybe using sample points

https://docs.gimp.org/en/gimp-sample-point-dialog.html

   

[Espermaschine]

I have worked with sample points, when i tried to get matching skintones and found it difficult.
Will have to give it another try.

[Ofnuts]

The Curves tool has everything needed:

   

[Espermaschine]

Cool, thanks !

Reading the Histogram is still something im not good at.
Had to switch to Logarithmic Mode, too.

I can get the gray to the desired level and adjusting the image more to its former state by sampling the white and black points.
However the red doesnt adjust as expected.
Why is that ?

[Ofnuts]

(01-10-2018, 08:46 AM)Espermaschine Wrote: Cool, thanks !

Reading the Histogram is still something im not good at.
Had to switch to Logarithmic Mode, too.

I can get the gray to the desired level and adjusting the image more to its former state by sampling the white and black points.
However the red doesnt adjust as expected.
Why is that ?

Define "Expected"

[Espermaschine]

(01-10-2018, 08:53 AM)Ofnuts Wrote: Define "Expected"

Well i treated the image with a random curve, so i cant tell you what it looked like, but it must be possible to reverse engineer the image to its former state, right ?

[Ofnuts]

(01-10-2018, 08:56 AM)Espermaschine Wrote:

(01-10-2018, 08:53 AM)Ofnuts Wrote: Define "Expected"

Well i treated the image with a random curve, so i cant tell you what it looked like, but it must be possible to reverse engineer the image to its former state, right ?

No, because every use of the Color tools (Curves, Levels, Brightness/Contrast, Hue/Saturation...) reduces colors (some different values in the input are mapped to identical values in the output) so you cannot get exactly back You can eyeball something that could look like the original, but i won't be the original (and wil have even less colors than the intermediate version, for the same reason).

[Espermaschine]

Oh, okay.
Good to know !