leigh
07-08-2003, 04:38 PM
PHOTOREALISTIC TEXTURING FOR DUMMIES
Part 6
Translucency, Transparency and Refraction
Foreword
Sorry that it has been so long since the last Dummies tutorial, but, as many of you know, I have been very busy writing a book on texturing for LightWave. I’ve received a lot of emails asking if these Dummies articles/tutorials are going to be in that book, and the answer is…no. These little articles I write are purely for giving people a grounding and basic understanding of these texturing principles and concepts. The book I am writing is a lot more detailed and practical. A lot of people have been disappointed that I am writing a LW-specific texturing book as I received many, many requests to do a “Texturing For Dummies” type book, but when my LW book is done I want to do one on painting textures in Photoshop, so hang in there…
Well, I hope that you all enjoy this latest installment! I kinda knocked it up pretty quickly this morning when I suddenly had the urge to do something nice for the community again.
I’ll put together a PDF version of this as soon as I can.
What is Translucency
Yes, what is it? Translucency, simply put, is the ability for an object to have light travel through it, or into it to a certain degree, resulting in it appearing to be backlit (in the case of a curtain or sheet), or to appear to have some faint luminous quality of its own (as seen particularly in skin).
As we know, when light hits surfaces, it is bounced (reflected) back off the surface. Well, in the case of translucent surfaces, some of that light travels through the surface as well. This phenomenon occurs in most substances in this world, except metals and most woods.
Imagine a theatre stage with its curtains drawn. If you were to place strong lighting from the back of the stage, you would be able to discern shapes behind the curtain without actually being able to see any real details in those shapes. It’s almost as if you can see the shadowy outlines of things. That is an example of translucency, as the material that the stage curtains are made of is translucent, allowing you to be able to see shapes through it when properly lit.
Take a look at the following image. This is my own hurriedly put-together theatre simulation experience involving a bunch of Lord Of The Rings action figures and a piece of paper.
http://leigh.cgcommunity.com/site_images/dummies/part6/pt6_01.jpg
This is different to transparency because the surface is not see through as such, and so you can’t actually see things in as much clarity and detail as you would when looking through glass. This is because you are predominantly seeing the shadows of those objects behind the curtains being projected onto them. If the curtains were made out of metal or wood, which are not translucent, we wouldn’t be able to see them. Apart from the shadows, you can also sometimes make out the faint colours of things through the curtains, especially if those objects are fairly close behind the curtain.
Another great example of translucency is when you shine a very strong light under your hand when it is dark, and you can make out faint details beneath the skin. This is because your skin is quite translucent.
http://leigh.cgcommunity.com/site_images/dummies/part6/pt6_02.jpg
Notice how the veins appear darker in the photo, because they interrupt the travel of light through the surface. If the light was stronger, you would also be able to see the outlines of the bones, because the bones would also interrupt the light.
Using translucency in your surfaces
Okay, so now that we know what translucency is, just how do we go about making textures that make our surfaces behave in this way?
Well, one way would simply be to go to your material editor and increase its translucency amount. By default, your translucent value would be 0 in all packages, since this one is not a universal surface property. Obviously increasing this value makes your surface more and more translucent, allowing more and more light to travel through it.
Note: To my knowledge, most (if not all) of the major 3D packages have translucency included these days in their surface editors, so just look for it and you’ll find it somewhere. In the case of programs like Max that separate raytracing surfaces from normal scanline ones, you might have to look in your advanced (ray traced) surfaces panels for a translucency channel.
Simply altering this overall value can be cool for quickly establishing a decent translucency for the surface as a whole, when it is applied to a surface that doesn’t really have major variations in this surface attribute, such as really basic clothing, curtaining, flags, candles… you get the picture. Although these could have extra details added by creating an actual texture map for it, you could still get away with just altering the overall amount in these cases.
But, of course, my favourite way of using translucency is to paint a nice translucency map! Aaaah, nothing beats a nice detailed map with little veins and things in it.
Okay, so let’s imagine that you have to make a texture for a dinosaur-like creatures wing. You could paint some really cool colour maps and whatnot for it and get it looking okay, but think about it – the membranes of the wings would be pretty translucent, wouldn’t they? Well, the arm bits of the wings would be translucent too, but lets not worry too much about those in this case.
So, to make all the little veins in the translucency map so that they will show up when the light is hitting the wing from behind, we would do something like the example below.
http://leigh.cgcommunity.com/site_images/dummies/part6/pt6_03.jpg
As you can see, it’s actually pretty simple. Make lighter shades of gray where you want the light to shine through nicely, and “block” the translucency by adding any darker areas, such as the veins.
I keep hearing about this thing called Sub Surface Scattering – what is it??
Okay, now onto sub surface scattering. Where we have any degree of translucency, we find the phenomenon known as sub surface scattering, more commonly referred to as SSS.
I don’t have lots of time to really go into detail about this now, but very simply put, SSS is when light rays penetrate a surface at a particular angle, and then kinda bounce around a bit inside the surface and then leave it at a different angle to that which it entered at, which causes the surface to appear as if it has some illumination of its own. Using this effect can give a lot of substance to an otherwise really flat looking surface, which is particularly useful for substances like skin, milk, wax, etc.
These days, SSS is usually implemented by using special renderers or plugins. Most of the major 3D applications have a plugin available for this, or some form of implementation.
Since I do not have any SSS plugins of my own right now, I cannot give you any examples here… boohoo. But I suggest doing a bit of research on it on your own – go to Google.com and do a search on it. There are lots of interesting articles about it on the Internet.
And that pretty much sums up the basics of translucency!
Part 6
Translucency, Transparency and Refraction
Foreword
Sorry that it has been so long since the last Dummies tutorial, but, as many of you know, I have been very busy writing a book on texturing for LightWave. I’ve received a lot of emails asking if these Dummies articles/tutorials are going to be in that book, and the answer is…no. These little articles I write are purely for giving people a grounding and basic understanding of these texturing principles and concepts. The book I am writing is a lot more detailed and practical. A lot of people have been disappointed that I am writing a LW-specific texturing book as I received many, many requests to do a “Texturing For Dummies” type book, but when my LW book is done I want to do one on painting textures in Photoshop, so hang in there…
Well, I hope that you all enjoy this latest installment! I kinda knocked it up pretty quickly this morning when I suddenly had the urge to do something nice for the community again.
I’ll put together a PDF version of this as soon as I can.
What is Translucency
Yes, what is it? Translucency, simply put, is the ability for an object to have light travel through it, or into it to a certain degree, resulting in it appearing to be backlit (in the case of a curtain or sheet), or to appear to have some faint luminous quality of its own (as seen particularly in skin).
As we know, when light hits surfaces, it is bounced (reflected) back off the surface. Well, in the case of translucent surfaces, some of that light travels through the surface as well. This phenomenon occurs in most substances in this world, except metals and most woods.
Imagine a theatre stage with its curtains drawn. If you were to place strong lighting from the back of the stage, you would be able to discern shapes behind the curtain without actually being able to see any real details in those shapes. It’s almost as if you can see the shadowy outlines of things. That is an example of translucency, as the material that the stage curtains are made of is translucent, allowing you to be able to see shapes through it when properly lit.
Take a look at the following image. This is my own hurriedly put-together theatre simulation experience involving a bunch of Lord Of The Rings action figures and a piece of paper.
http://leigh.cgcommunity.com/site_images/dummies/part6/pt6_01.jpg
This is different to transparency because the surface is not see through as such, and so you can’t actually see things in as much clarity and detail as you would when looking through glass. This is because you are predominantly seeing the shadows of those objects behind the curtains being projected onto them. If the curtains were made out of metal or wood, which are not translucent, we wouldn’t be able to see them. Apart from the shadows, you can also sometimes make out the faint colours of things through the curtains, especially if those objects are fairly close behind the curtain.
Another great example of translucency is when you shine a very strong light under your hand when it is dark, and you can make out faint details beneath the skin. This is because your skin is quite translucent.
http://leigh.cgcommunity.com/site_images/dummies/part6/pt6_02.jpg
Notice how the veins appear darker in the photo, because they interrupt the travel of light through the surface. If the light was stronger, you would also be able to see the outlines of the bones, because the bones would also interrupt the light.
Using translucency in your surfaces
Okay, so now that we know what translucency is, just how do we go about making textures that make our surfaces behave in this way?
Well, one way would simply be to go to your material editor and increase its translucency amount. By default, your translucent value would be 0 in all packages, since this one is not a universal surface property. Obviously increasing this value makes your surface more and more translucent, allowing more and more light to travel through it.
Note: To my knowledge, most (if not all) of the major 3D packages have translucency included these days in their surface editors, so just look for it and you’ll find it somewhere. In the case of programs like Max that separate raytracing surfaces from normal scanline ones, you might have to look in your advanced (ray traced) surfaces panels for a translucency channel.
Simply altering this overall value can be cool for quickly establishing a decent translucency for the surface as a whole, when it is applied to a surface that doesn’t really have major variations in this surface attribute, such as really basic clothing, curtaining, flags, candles… you get the picture. Although these could have extra details added by creating an actual texture map for it, you could still get away with just altering the overall amount in these cases.
But, of course, my favourite way of using translucency is to paint a nice translucency map! Aaaah, nothing beats a nice detailed map with little veins and things in it.
Okay, so let’s imagine that you have to make a texture for a dinosaur-like creatures wing. You could paint some really cool colour maps and whatnot for it and get it looking okay, but think about it – the membranes of the wings would be pretty translucent, wouldn’t they? Well, the arm bits of the wings would be translucent too, but lets not worry too much about those in this case.
So, to make all the little veins in the translucency map so that they will show up when the light is hitting the wing from behind, we would do something like the example below.
http://leigh.cgcommunity.com/site_images/dummies/part6/pt6_03.jpg
As you can see, it’s actually pretty simple. Make lighter shades of gray where you want the light to shine through nicely, and “block” the translucency by adding any darker areas, such as the veins.
I keep hearing about this thing called Sub Surface Scattering – what is it??
Okay, now onto sub surface scattering. Where we have any degree of translucency, we find the phenomenon known as sub surface scattering, more commonly referred to as SSS.
I don’t have lots of time to really go into detail about this now, but very simply put, SSS is when light rays penetrate a surface at a particular angle, and then kinda bounce around a bit inside the surface and then leave it at a different angle to that which it entered at, which causes the surface to appear as if it has some illumination of its own. Using this effect can give a lot of substance to an otherwise really flat looking surface, which is particularly useful for substances like skin, milk, wax, etc.
These days, SSS is usually implemented by using special renderers or plugins. Most of the major 3D applications have a plugin available for this, or some form of implementation.
Since I do not have any SSS plugins of my own right now, I cannot give you any examples here… boohoo. But I suggest doing a bit of research on it on your own – go to Google.com and do a search on it. There are lots of interesting articles about it on the Internet.
And that pretty much sums up the basics of translucency!