I have some very nice MR's I've perchased here.  I noticed the odd difference between the bump maps and the displacement maps.  One is light in contrast the other dark.  Anyone care to clarify why this is so I can use them properly. thank you.

Boni

Numerically, bump and displacement mean exactly the same thing. They differ in implementation.

Assuming we're dealing only with Poser (and not other apps) and that users know how Poser shaders work, these two maps differ in overall height. The brighter one means to generally be higher than the darker one.

However, there's a metric ton of Poser users who don't understand either the maps, the math, or how you would properly go about making these.

You may be asking too much of me to tell you what they (people who made those maps) intended, since it is highly likely they have no idea what they said.

If they made the maps from gray-scaling the color map, they are clueless and the maps don't mean anything at all.

Bump and displacement maps both have a zero elevation level. For Poser this must be black. For other software packages (such as ZBrush) the zero elevation is mid grey. For bump maps it doers not really matter, you just lower the strength and you have the bump (not really, but usually close enough). For displacement maps it does matter and you need to correct for it since mid grey will raise the geometry in Poser. The easiest thing to do is to add a subtract color node and subtract mid grey from the displacement map - so mid grey becomes black. Especially if you have multiple material zones you need to do that to have a correct alignment.

Perhaps you show me mat room screen shots and I can disambiguate.

Generally speaking, however:

The numerical value of a map is an indication of what proportion to move the surface (actually move [displacement] or pretend to move [bump]) from its bottom or lowest value.

Black, which is zero, means don't move it at all.

White, which is one, means move to 100% (the top) of the indicated bump or displacement range.

Other than Poser, many apps declare a different interpretation. They say that .5 (mid-gray) means don't move from the nominal, original position. 1 means move the maximum amount above the original position, and 0 means move the maximum amount below.

In other words, for Poser, black means don't move, and white means move the most. Other apps, black means move down the most, white means move up the most.

We deal with either scenario by a little arithmetic. We subtract .5 from a mid-gray is no-move type of map and Poser behaves the same as the others.

Bump and displacement maps both have a zero elevation level. For Poser this must be black. For other software packages (such as ZBrush) the zero elevation is mid grey. For bump maps it doers not really matter, you just lower the strength and you have the bump (not really, but usually close enough). For displacement maps it does matter and you need to correct for it since mid grey will raise the geometry in Poser. The easiest thing to do is to add a subtract color node and subtract mid grey from the displacement map - so mid grey becomes black. Especially if you have multiple material zones you need to do that to have a correct alignment.

Unless you enable gamma correction. Then subtracting 186, 186, 186 is what you should do, assuming you correctly set the gamma of the map to 1. We can't set the gamma of color chips, so you'd have to compensate before subtracting. This is why I suggest subtracting with Math, not Color_Math - then you subtract .5 (always, no matter what) and have no issues with gamma.

Here is what I do understand.  bump creates an illusion of depth that is lost on the edges ... dipplacement effects the mesh and creates a more true tactile texture change.  Here is what I have set up.  I've isolated the bump/disp. settings and added a stand-alone node to show the "other" bump map to show my question.  Why do they seem to contradict each other?

I am customizing a map and want to alter it to create a more accurate bump for my character.  Just so you know my ultimate goal. Watermark added to protect resource. :) (sheesh, had to edit for grammar's sake)

I know a wee little bit.

What I've always been told is that in most programs bump just makes the appearance of added/sculpted geometry. Whereas, a displacement map actually pushes/pulls at the geometry and changes it enough that the details are more realistic.

Having worked with LIghtwave I do understand that part.  My confusion is the odd differences in the maps and the purpose of those differences AND how to I utilize that in my own shader set for my character.  A lot of people use a combination of bump and displacement.  I do get that ... displacement alone can do hideous things to the mesh if you push it too far and off setting that with a bump helps.  It's just the maps seem to contradict each other.

I use bump maps for smaller changes, like dimples or rough parts. If a change is big enough to alter the shape, I use displacement, but usually with 32 bit images from ZBrush. For pores and dimples, bump is enough for me, but you can use the displacement channel as well. With low settings it does not make much of a difference, if the bump map does not have problems.

Many of the displacement and bump maps I've got with bought products here are just desaturated diffuse maps, which don't work that well for me. The map you posted above seems to be generated from the diffuse map and may have problems. I see two white spots on the nose, for example, which means you will have two dimples there. Is that really intended? That looks like a burned-in highlight from the diffuse map (which should not be in the texture anyway), but in my opinion its absolutely wrong in a bump or displacement map. 

If anyone could give me a pointer to a vendor who produces good bump or displacement maps with his/her products, I would be very glad.

Neither of those look like bump maps to me!

The 'alternate' looks like a desaturation of the diffuse and the 'displacement' map you're using looks like a simple inversion of of that desaturated map.

Anyone use math subtract with bump, or is that of negligible usefulness?

Other than Poser, many apps declare a different interpretation. They say that .5 (mid-gray) means don't move from the nominal, original position. 1 means move the maximum amount above the original position, and 0 means move the maximum amount below.

In other words, for Poser, black means don't move, and white means move the most. Other apps, black means move down the most, white means move up the most.

We deal with either scenario by a little arithmetic. We subtract .5 from a mid-gray is no-move type of map and Poser behaves the same as the others.

Of the relatively limited number of apps I know, none explicitly sets a value for mid grey (which would essentially break the range into two gradients). They set the black and white values, the mid-grey is then implicitly set as the mid-point of the range (and if the black point is equal and opposite to the white mid-grey will be the zero point).

In Zbrush the user can define the mid-grey point. By default it is set at 0.5

I usually use the color picker to pick up the mid grey point in the color subtraction

If you subtract .5 from the bump or displacement where nominal is pure black, will this give you negative values in bump or displacement?

to my knowledge, understanding and just performed tests, bump black still means inward, bump white still means outward and mid grey acts as some sort of neutral. The bump value stands for the max effect, so a value of 0.1 means 0.1 in and 0.1 out, the black/white distance is 0.2.

Displacement black still means no displacement, displacement white means max displacement, either outward (positive displacement value) or inward (negative value). A 0.1 value means a black/white distance of 0.1. Poser displacement completely differs from Octane displacement, which is always outward but can have an inward offset.

In order to use a bump map for displacement - in Poser, one has to subtract 0.5 (and of courde, set Gamma=1 for the map) and double the value, as the bump-range is twice the displacment range. When a positive displacement value is used, and a negative result comes from map & subtraction, then that portion of the displacement in inward indeed while other portions are outward.

At render time, displacement actually displaces polygon elements which implies that Min Shading Rate in render settings should match (or exceed) the resolution of the map.

Up till now I've not been able to set up bump and displacement so that they make indistinguishable results - even at some distance.

Effects of displacement and especially bump are seriously affected by GC, IDL and SSS as displacement and especially exist by the grace of light & shadow contrasts, while GC, IDL and SSS tend to reduce those contrasts. As a consequence, bump/displacement values might need some increase. In practise, under GC/IDL/SSS conditions, I've found it beneficial to combine bump and displacement. This does not double the effect, but the bump brings back contrasts into displacement that SSS have taken out.

So... did something change during my winter sleep? I am on PPro 2014 SR 5.2, btw. 

This is a displacement map. Color subtracted by means of color subtract with the mid gray picked from the image. The black lines curve into the cube and the white lines are raised. Grey is neutral here

Same thing happens with bump maps (but obviously not as good as displacement maps)

And for octane the offset needs to be half the height and negative to compensate for the neutral level

For both Poser and octane the gamma wast set to 1 for the displacement maps. If the gamma is not 1, the displacement will not be linear

Can this setup using multiply (from an older thread) be used to mask bump as well? 

http://www.renderosity.com/mod/forumpro/?thread_id=2841686#msg3877290

the multiply node can be used to mask off a section from the displacement or bump map. That is a solution to another problem. You could use a blend node as well with the option of applying two different maps or strengths to the same material zone

thanks for this, although I'm not sure what exactly is the point.

My notes:

 * in Poser one can have negative Displacement (Height) values, in Octane one can't. To turn white spots on the image into dents in the surface, Octane needs the inverse of the image instead. In your image, when I make an animation where the white elements move in and out while the black element moves in contrast, in Poser I can simply animate the displacement value from -1 to +1 and back. In Octane I have to do it a different way.

 *  Bump and displacement are values, there is no need for the (gamma sensitive) color_math. I just use math_function instead, and subtract 0.5.

 * Displacement does alter the size of an object, and 0 means "none", whatever the way it's derived. Putting a non-displaced object next to a displaced one immediately demonstrates the meaning of neutral. With Bump this is different. Within the area covered by a bump-map, shadows will get distorted in a relative way (so a positive bump value black will look deeper than grey, and white will look higher than grey. As demonstrated in Wims images above). When putting a bumped and non-bumped object next to each other, the boundary between the surfaces will not reveal any depth info. Bump-neutral has no meaning outside the mapped region.

<image goes here, I hope. left cube has no bump, right cube has a lot, made by Tile node with black and white tiles and midgrey in between. At the boundary, there are no in/out revealing highlights or shadows> 

 for the sake of it, same two cubes, from a different angle, using displacement now.

the reason i used a color math subtraction is that I then can use any mid grey displacement map. If the creator used a different level (as you can do in some apps, or when it is calculated as the middle between minimum and max) it will still work.

Mat_room setup, forcing a 50% grey and subtracting 0.5 for neutral, in a gamma-insensitive way.

BTW: the cube has a 3-level subdivision to enable neat edges around the tiles. 

Wim, I understand the color-subtraction but... either you must use render gamma on the bump map (not a good idea) or apply a gamma inversion on the grey swatch, either manual (as BB suggests, somewhat tedious) or by inserting the gamma node. Otherwise the swatch gets darkened before rendering while the bump map will not, and the subtraction goes wrong. Unless you switch off GC at all, of course.

@DeathMetalDesk: as Wim says. You can do anything, the surface element at the spot is just displaced (in a direction dictated by the surface normal) by any value that comes out of your node tree, multiplied by the displacement value. Do note however, that this displacement value is measured in your local Poser units. So when you're using inches (like BB does), 1.0 means 1" while when using meters (like I do), 1.0 means 1 meter. This must be taken into consideration when implementing node-tree setups from other users.

Wim, I understand the color-subtraction but... either you must use render gamma on the bump map (not a good idea) or apply a gamma inversion on the grey swatch, either manual (as BB suggests, somewhat tedious) or by inserting the gamma node. Otherwise the swatch gets darkened before rendering while the bump map will not, and the subtraction goes wrong. Unless you switch off GC at all, of course.

For me the color picker picks up the color in the right gamma, so no need for an additional gamma node

Been away a couple days ... what you guys have done here is a great help ... and to a lot of people looking for verification.  Thank you ... keep it coming! :)