Texturing is where we give our 3D models their materials. This is where we turn a blank wall into one made of brick, granite or wood.
There is a clearly defined division of labor in computer-generated imagery between 3D modeling and texturing. The main reason for this is that the easiest way to give a model its material definition is to use photographs taken in the real world. So instead of modeling each brick in a wall, we create a flat plane and project a photograph of a brick wall onto the model. This is referred to as texturing, and there are two broad categories used in 3D architectural visualizations: those based on color and those based on texture maps.
This is the simplest method of defining a surface and is what it sounds like: applying a field of color to a 3D object. Colors are defined within the software using a control panel that adjusts various color components, for example RGB or HSV. Materials based upon color alone are used in architectural renderings, but color alone will not create photo-realistic materials; other surface qualities must be added, such as specularity, reflectance, bump and opacity to render a believable material. Those properties are discussed later in this section.
This is by far the most common method of creating materials for 3D architectural imagery. This category goes by several names – “texture maps” is the most common, but the terms “maps” and “bitmaps” are also used. Texture maps come in two main varieties: image based and procedural.
Image based textures are photographs that are projected onto a 3D model. To expand on the brick wall example cited above, one could model thousands of individual bricks. The shortcomings to this method are numerous: it’s time-consuming, and the file size can get large and unmanageable. The industry-standard procedure is to create a completely flat surface, and then project a photograph of a brick wall onto the surface. This method is simple, quick to model, and results in small file sizes.
There are a couple of downsides to this method. The illusion will break down if you get too close because one will be able to see that the surface is indeed flat and not three dimensional like a true brick wall. (Recent advances in rendering technology can correct this problem – see displacement mapping.) The other persistent problem to this method is known as “tiling”. Tiling is the observable repetition of a texture over a surface. If my brick wall is 100′ long, and the brick photo I’m using to texture it is 5′ long, I have to repeat (aka “tile”) that photo 20 times. If there is variation in the photo, say a splotch in the upper left corner, then the eye will start to see not just the bricks, but a noticeable repeat of the splotch over and over again. The obvious remedy is to take a photo of a 100′ brick wall, but this is an unwieldy solution because the file size of such a photo gets to be quite large and memory intensive. The industry standard approach is to use “tileable” texture maps. These are photos that have been processed, usually by hand, to correct splotches or misalignments. When done well, tileable textures can be completely convincing.
It’s worth noting that texture maps don’t have to be still, but can be drawn from animated sources, like pre-recorded videos. For example, that’s how we create a roaring fire in an interior animation panning past a fireplace.
Procedural textures (also known as “parametric”) are ones that are defined completely by software code. A seminal example in 3DS Max is the “noise” texture. Noise is generated by using a software algorhythm that mimics fractal-like patterns often seen in nature, for example the wave pattern on the surface of water. 3DS Max comes with several dozen parametric textures, for example, checker, dent, marble, smoke and wood. The problem inherent in most of these parametric textures is that they tend to look unrealistic when used with their default values. Their primary utility is as a base to which one adds other textures, sometimes several layers deep, only then do the resulting materials start to look realistic.
From Textures to Materials
It’s not our intention to get bogged down in nomenclature and terminology, but it’s important to clarify the terms “texture” and “material”. Using the analogy of a cookbook, materials are like recipes and textures are like ingredients. Like a recipe, materials contain a set of instructions on how to combine ingredients, the ingredients in this case being the visual characteristics of objects. So, in addition to defining the texture, here’s a list of the visual characteristics that materials define:
In all 3D production studios, materials are defined and then saved to libraries. Our studio has several thousand materials at our disposal, containing every category seen in 3D architectural imagery: brick, stone, steel, glass, tile, wood floors, grass, ground cover, leaves, flowers – the list is vast. This makes the process of texturing pretty efficient. When applying textures to a client’s model, materials are almost never created from scratch. Instead, the materials are pulled from a library and then modified as required to get the look exactly right.