View Full Version : I just don't get gradients can anyone help me?

01-14-2005, 04:59 AM
I've been looking into gradients as I want to create some realistic skin. From what I can tell some of the input parameters make sense. So for example setting the input param to bump within the colour texture options would mean anything at a certain bump height would create the colour on the graph. I tried this last night and created a graph with white at the top fading to red in the middle and then blue at the bottom. I had a bumpmap which I assumed it would reference. But all it did was to create a blue object. I thought logically that the highest point in the bump map would be blue then maybe mid points would be red and then the area of flatness would be white. The only time I got it to work was to move the red key right near to the bottom as well. Why is this, surely the graph should relate to the bumpmap so say the blackest part of my bump map would equal the bottom of the graph where as the whitest part would equal the top of the graph? Actually saying that I guess it might be the other way round but evven so I should still see other colours aprt from blue? The thing is this isn't even what I wanted it to do I was just checking that I'd grasped the basics. I really want to use surface thickness but I haven't got a clue how you relate this to the graph. How does it decide what part of the graph is the part of the object, I don't think my brain wants to get it. It has a distance at the bottom of the graph, if I change this is it relating to how thick I want the surface to be?
Can anyone clear this up for me in an easy way to understand, well for someone stupid like me :)
And also has anyone actually got a good SSS effect from using surface thickness?

Cheers in advance.


01-14-2005, 05:17 AM
If you combine gradients in different material channels, you certainly can get something like a SSS look. It looks in most cases a bit ethereal and not physically correct, though. The distance is measured perpendicular to the normal of the polygon, but in the opposite direction (facing away). so it is essential to model your meshes in equivalent realworld units and proportions.

As for bump gradients - perhaps you are simply using the wrong settings for your bump. The colors will not be mapped corresponding to the gray levels in you texture - that would be "Previous layer". The coloring is evaluated based on the ray direction of the bump map that creates the "elevation" so even very subtle textures can have a great effect. On the other hand very strong bump maps cannot show any effect because their rays intersect and yield the same values all over the place resulting in the same color everywhere (not exactly, but as the eye perceives it and is incapable of detecting those faint variations). Always tweak your bump first, not the color gradient.


01-14-2005, 05:52 AM
Sounds pretty complex I wish it was a bit more friendly. I still don't really get it. If I set my surface thickness to 3mm which would be 3mm perpendicular to the normal of the poly and I set this in the transparency setting what exactly would it do? I just don't get it, it makes no sense. Say I've set the bottom of the graph to black at 3mm what does this mean, does it mean that the surface will be transparent. If so what is the relevance of the distance it can't be 3mm from the camera because that's a seperate setting?

01-14-2005, 07:00 AM
go here: http://www.newtek.com/products/lightwave/tutorials/videos/index.html and download the gradient tutorials at the bottom. You will see that the bump input parmater has nothing to do with the bump height but only with the pattern used to create the bump. Even if the bump has no heigt, the bump input parameter still works.

01-14-2005, 09:38 AM
Hey thanks spec24 I'm downlaoding it now, looks like it might be just what I need.

Cheers for the replies, hopefully that will sort me out.


01-14-2005, 10:59 AM
no problem peteb - make sure you get both of them as they are both pretty informative.

01-16-2005, 06:30 AM
Ok that's cleared up a lot about how things work, although I sitll argue that they should make it more logical and should write a lot more informative chapter on gradients in the manual because at the moment it really doesn't make things that clear.
Another question though is in the video at the end the guy goes to say that in the next lesson they'll be covering slope gradients but then when I looked for the video there's no more. Are these videos just tasters of some video dvd that you can buy or did they just not get round to doing them? I think they're really good and the more there are the better.


01-16-2005, 08:05 AM
no - I just don't think they got around to it. I agree, those videos are great and I think NT would be wise to make more. I think it would be nice if NT was able to put more of these videos out to show the basics, and then studios like Kurv could focus on how these tools are implemented instead of how they actually work (like IK Booster :) )

01-16-2005, 11:30 AM
So true, this is one of my biggest gripes with software. Because all software is made by programmers, generally the logic behind it is thought up by programmers. I only speak for myself but from an artist point of view I find a lot of tools very confusing to use. I work in the games industry and we have a lot of in house programs. The amount of times I see tools that the programmers implement in such a complex way that for someone who really doesn't get math it seems mind boggling. Isn't it ironic that to create a program for artist's it's made by people that usually use the complete other side of their brain? That sounded like an insult but I didn't mean it that way. All I'm saying is that in my experience programmers are so logical that it far exceeds my perception of how things should be, I'm an artist I got a D grade twice in Math, my brain is not wired that way. When I use something I expect it to work the same way things work in the real world. I can venture into the Left side of my brain to a certain extent to grasp the simplest of mathematical equations. For example 5+5 is 10 :)
But don't give me anything that looks like the times table has just fallen into the alphabet because that will just mash my brain up.
What's worse is the fact that most programs have been made by many programmers over many years and you find that one tool will make total sense while another will just seems totally backwards.
I find they also use terms for the buttons that were used in the mathematical papers they came from. Now as a science point of view this is fair enough but it really doesn't give me any idea of what it does. And when writing for a program that will be used for an artist I think making things clear is essential. There are only two programs I use which I find totally logical and do what I expect when I've read the manuals. One is photoshop, and the other is Z-brush A lot of people find Z-brush really weird to get round but I simply think this is because it's been laid out the way an artist would want to work. Once you get going on it it's such an easy piece of software to use. I'll read the tutorial and then do it and it will work.
Don't get me wrong some bits of Lightwave are good and easy to understand, and obviously being a huge program makes it hard to keep everything flowing. But I really do believe that more artists need to have an input in how things should work. You could say I'm being really stubborn and should just read the manuals, believe me I've tried and sometimes I'm more confused then when I started. I truly believe that every program no matter how complex can be easy to learn it's just a matter of tailoring for the end user and in Lightwaves case it's a creative person.
If things really do need to be complex then I wish that the programmers would write an in depth tutorial on how to use it and write it in a down to earth way.

Right that's got that off my chest, sorry about that. Would be nice to hear other peoples views on this though.


01-17-2005, 01:28 PM
Here is a nice gradients explanation


It's in the know how section also there is one at http://www.the-worms-of-art.com



01-17-2005, 04:30 PM
Hey thanks Munky that's a good site.