So, you’re making your own textures now? Great! You’ve probably become familiar with the diffuse or color maps and are starting to wonder what the other channels like specular do.
Specular maps are black and white images in non-PBR materials that determine the shininess or reflectivity of an object in 3D. It’s used in conjunction with a diffuse and normal map to enhance the realism of the object’s texture.
Specular maps are a huge deal in texturing and can really make or break the final look of your 3D object or environment. Knowing how to use and manipulate specular maps is a great an important skill to have as a 3D artist, and here are the details:
What Are Specular Maps?
Specular maps are used to define the shininess/highlight on a surface. Typically a specular map is a black and white image that maps out the shininess value on an object. The whiter the pixel, the more shiny the object in that specific place on the texture (or on the texel).
Therefore, textures that arent shiny and that are more matt like stone or fabrics would have a very dark specular map. While other more shiny materials like chrome or plastic would have very bright specular maps.
You can play with the contrast of the specular map to make the highlights more intense to create interest in your objects. A specular map with high contrast will cause your object’s shininess to be more intense and deliberate, while a less contrasted image will mean your entire object will look shiny but a little bit shinier on other places. Only the very black areas of your image will mean that there is no shininess in that texel.
So what does specularity look like in real life? Well, generally, you will want to ask yourself what is the brightest spot on the object. It might also indicate where exactly the light is coming from. Here are some examples;
The Difference Between Specular and Glossy
Specular maps determine how much light will reflect off of a surface. In the range of black and white values, the whiter area will reflect more light, and the blacker areas less light. Gloss, on the other hand, determines how clear that reflection will be.
How to Make a Good Specular Map
- First, ask yourself where you might expect the shininess of an object to be. Where would the object be glossy, where not? If the object is shiny, why is that? Is the object wet? Smooth? Greasy?
- Make a copy of the original diffuse.
- Desaturate the images using any photo editor. You can use any free photo editor like GIMP.
- Go to Filters > Generic > High Pass Filter.
- Set your filter radius to 200 and preserve DC.
- Go to Colors > Curves and play with the contrast of your image
- Reinforce the specular with a good bump, displacement or normal map
What Is The Difference Between Using A Specular Map or Just Using Specular Lighting in The Shader Itself?
To understand this, you will have to understand how light behaves in a 3D environment. Think about it this way – if you are standing outside with a shiny sphere and the light is coming from the left, the specular point of the object will be on the left. Now, imagine you had to walk to the other side of the object. The specular point on the object will move as your perspective of the sphere changes as well.
This is essentially the problem with painting specularity onto a diffuse map. If you do this, the specularity/reflection of the object will not move as you move. This becomes a problem in real-time, like in games, where you can move around objects. If your reflection is static, your 3D object might render a lot quicker but will not look realistic.
Therefore, its a way better idea to make use of specular maps. But specular maps are also not always necessary. And we can have a look at that next;
When Isn’t a Specular Map Necessary?
Well, these days, PBR materials are super popular. And when you’re using PBR, you often replace your specularity with a roughness map. The specularity of an object is automatic and you need to tell your engine where your object has no specularity, so basically you simply indicate the opposite.
You will only be making and using specular maps in ‘old school’ shading techniques like when using Blinn / Phong shading types – which are still super handy and beautiful. Some will even argue that using a specular map gives the artist way more control over the shininess in objects like metals, as opposed to using Metallic maps.