Help getting started with customizing bump map for Daz V4 model

U_Iuiko

We've looked around a lot for clear documentation or tutorials on this but haven't found anything that's complete enough for beginners.  We'd like to start by making a fairly simply change to an existing file, just to get a feel for the process.  It sounds like the file we need to modify is the bump file, which is the one that flattens out the skin in black and white.  Is that correct?  In the case of the model we're trying to modify now that's a .jpg file.  We opened that file in Gimp, randomly

According to an article on the web, written for an earlier version of Daz (we're in 4.8 pro), we should then load the character and select it, select the "Surfaces" tab, then select the character from the list (we select 2_SkinTorso, since we edited the torso file).  Then, it says to find the "Bump Strength" control, click the arrow, choose "Browse" and select the modified file.  The article says "that's it!" -- but nothing happens for us.  Is there a step missing?  Is there better documentation for this somewhere we haven't found?

Richard Haseltine

What do you mean nothing happens - does the map faile to change, or does it chnage but not show any difference in renders? How did you modify the bump map?

U_Iuiko

I'm not sure I understand the question.  I can see that the alternate map file is selected but there's no difference in the appearance of the character (at this point, a fairly basic V4).  We're complete rank beginners at this, so to test the concept we simply used an airbrush tool to add some black spots on the file (on the abdomen), and expected them to show up as raised (or is it lowered?) areas.  But there's no change at all that we can see.

SixDs

There are two things potentially at work. First, the effect of your bump maps are not going to show up in the preview window unless you do a spot render. They will show up in a finished render. However, the degree to which the bump maps affect the render will depend on a combination of three settings in the surfaces tab: Bump Strength, Negative Bump and Positive Bump. If you set Negative and Positive Bump equally, they'll cancel each other out and you'll get nothing. You can play with combinations until you achieve your desired affects.

I should add a couple of things just to clarify how the bump maps work. In DAZ Studio, a mid grey tone is neutral, with lighter areas appearing raised, and darker areas recessed. This is why DAZ Studio has settings for Positive and Negative Bump. (By contrast, in Poser, black areas are flat and everything lighter scales up from there - subtle but it means that bump maps created specifically for one program produce different results in the other)  You should also understand that using bump maps to create the appearance of surface relief is trickery, causing the render engine to produce shadows where none would otherwise exist (rather like creating the illusion of three dimensions on a flat piece of paper using a pencil to shade in shadows). The important thing to remember is that the appearance of relief will only exist when viewed straight-on, and will diminish and eventually disappear when viewing at increasingly extreme angles. Lastly, while editing an existing bump map in an image editing program by creating pure black (or pure white) dots may be useful in gaining an understanding of how bump maps work, you wouldn't necessarily want to be using either of those extremes for day-to-day purposes. The potential problem is that whenever you adjust the Bump settings in the Surfaces tab for a preset bump map in order to accentuate your additions, you are also going to be affecting the entire map (meaning all the original features on the map as well). So a better approach to adding bump features to an existing map would be to choose and use an appropriate greyscale tone. Its a skill like most of this stuff. :)

Richard Haseltine

SixDs said:

In DAZ Studio, a mid grey tone is neutral, with lighter areas appearing raised, and darker areas recessed. This is why DAZ Studio has settings for Positive and Negative Bump. (By contrast, in Poser, black areas are flat and everything lighter scales up from there - subtle but it means that bump maps created specifically for one program produce different results in the other)

It isn't that DS has hard-coded mid-grey as neutral, it's that by default Negative Bump is the opposite of Positive Bump. Black is Negative Bump, white is Positive Bump and the shades between are intermediate values. If, for example, you set Negative Bump to 0 and Positive Bump to 1 then mid-grey will be 0.5 (Poser-style).

U_Iuiko

Thanks for thorough answers.  The articles I read didn't say (or I missed) that changes in bump would only be visible when rendered.  In playing around with this further, we found that making changes to the 'diffuse color' map (not sure of the terminology) led to better results that are also visible in the viewport.

This is painstaking work.  I can see why those who can do it well are able to sell the results of their work.

SixDs

"we found that making changes to the 'diffuse color' map (not sure of the terminology) led to better results"

Weeeeellllll, I guess that depends on what you mean by "better results". Generally using a diffuse map as a bump map is considered to be undesireable in that not all the various greyscale info is going to be relevant to producing your desired relief, and could create potential issues. Not all features or gradients that exist in your diffuse map will relate to bumps, for example. An extreme example of this might be a birthmark, which could end up looking like a mole in your render.