It depends on how you create the map! Consider the following and let it sink in for a while before you go forward:
- The image is displayed with a gamma correction for the benefit of your eyes
- The data is still just data. The gamma correction is for the display part not the data part.
Now a bump map is pretty hard to draw with a paint application. Because its hard to see even if you were correctly linear. So you end up using such things as looking at values. Now here is the catch:
- If you decide that 128 is halfway in your intensity then that is reality. Since that is what your encoding into the data stream. The data is what you interpret it to be since its not meant for human eyes and the monitor. Who cares what the monitor shows the values as its all on how you interpret the data editing it in.
Making the bump/displacement map
Ok, so now I have described that the data is up to interpretation. But why would you interpret the data as linear? Because then you can design your side profile better. See what you can do is think of 100% opacity of your brush as the target height you want to carve or layer to. You can then use the curves tool to design the shape of your stamps brush (since you think the data is linear).
Image 1: A suction cup stamp.
Now if you do something like this then your image is linear despite what everybody tells you. You have decided to discard the image rules that says otherwise. And that is why the image is linear, the author chooses for it to be linear so its easier to work with.
Image 2: Same image displaced and interpreted linear (note I scaled the height a bit to fit to my default bb size), working as intended.
Technically linear is better.
A synthetic map has no benefit of compressing certain values on the expense of others. Linear is inherently better because the spread of your bump is better that way. Which is why you'd be wasting resources encoding it in a gamma corrected manner.
Secondly a image does not need to specify what color space it is in. Its just that image editors will assume it is sRGB encoded. You have no reason to do same interpretation, no info means just: "Nobody bothered to write down what they were thinking". So maybe the point should be made you should tag it linear. But here is the rub... your computer does not come with a easily accessible linear profile.
What about Photoshop and blur?
This is where it gets tricky. Photoshop tries to do quite much work to ensure that you do not need to know anything about this stuff. And this is where you shoot yourself in the foot. Se Photoshop is not meant for texture making, its meant to edit images not random data. So since blur on a image is different linear and nonlinear it wont work its geared to wrong data.
But you can do one of 2 things to fix this:
- Disable the gamma correction of blur
- set your working space to a linear profile
The reason you have a hard time with this is
- You do not know what other people think, you simply do not know if they should be gamma corrected or not.
- that your using a application that treats images as images
Point one is especially confusing. I just know that ALL my bump and displacement maps are in fact linear. But I can not know what your maps are. Odds are they are linear because its nearly universally understood that the data is linear. Even people who do not know about gamma tend to do it linear for bump/displacement for some reason (because its easy and that's what you think images are until somebody tells you otherwise).