Factors Involved in a 3D Image
There is, as I’ve demonstrated generally above, a lot that goes into rendering a 3D image. But, let’s look a bit at how we can go about making a 3D image appear realistic on a 2D screen. A number of factors go into this: 2D shapes, applying textures, applying environmental factors like lighting and perspective, and using anti-aliasing and interpolation to being smoothness to the image. Let’s go over this stuff, shall we?
Shapes
When you look at your screen, you will see a variety of 2D shapes. This is because all your screen is capable of rendering are 2D shapes. Even in the case of 3D, your monitor must display it through a 2D medium. Therefore, a technique is used to generate shapes which look 2D out of 2D shapes. All sorts of 2D shapes are used: circles, squares, triangles, etc. But, all of these shapes can be summed up with the term polygon. The word polygon comes from poly-, meaning “many”, and -gon, meaning “angles. A polygon, then, is any shape containing three or more line segments. A triangle is the simplest form.
Interestingly enough, any 3D object can be approximated through the use of polygons. In the case of rather detailed objects or those with a fine, curved surface, thousands of polygons might be needed to properly generated the surface. The larger the number of polygons, the more accurate the depiction will be. Smaller numbers of polygons will give a curved surface a more jagged look. To the right, you can see a kettle made up of a wire frame constructed of polygons. You can see that the more curved portions of the object, the handles, have a mugh higher density of smaller polygons in order to accurately depict the surface.
Textures
When you add a surface to a basic 3D wire frame, you begin to make it look like a 3D object. Think of it as if you are wrapping the wire frame with a paint job. With any texture, though, there are a variety of properties which the 3D artist can choose from. To show you, look at any object in the room in which you are reading this. Notice how every object has a different series of colors on it. Not only that, each has a different texture: smooth, slightly bumpy. The surface might be reflective, meaning other object in the space might be viewable as reflections on another object.
In 3D software, programmers use bitmaps as textures for their 3D worlds. They can assign a series of properties to each, and take advantage of certain abilities of the video card processor to perform manipulations for them. Here are a few:
- Alpha Blending. This is the method used by the card to blend two bitmaps together so that that one looks transparent. In order to understand this, lets look at this situation: imagine a checkered table cloth and a piece of blue transparent glass. When seeing this on a video card with alpha blending, you will see the table cloth behind the blue glass. This is successful blending of the two images so that it looks real.
- Filtering. This eliminates the blocks in a 3D image.
- Interpolation. This is where the video processor can interpolate on both the X and Y axis. This is very noticeable. On a card without interpolation, when you enlarge a video clip to full screen, the video will look choppy and jagged. the interpolation smoothes out the image, making it look realistic.
- Fogging. Pretty much like it sounds. This refers to the card’s ability to blend an object into a fixed color as it moves away, giving the ability to make the object look as if it is disappearing into the fog.
- MIP Mapping. This is the ability for the card to store several versions of a textured bitmap in order to quickly display the image in varying sizes. A prime example would be a game where you are approaching a textured wall. As you move toward it, the texture will appear to get larger. This will happen very quickly. Without MIP mapping, the textured wall will blink and sparkle as you approach while the chip continually recalculates the texture for the new size.
- Perspective Correct. This makes a textured 3D image look realistic from any angle.
- Texture Mapping. This puts a bitmap onto a 3D surface to make the object look more realistic. An example is in Microsoft Monster Truck Madness. The program continually throws a bitmap of sand onto the dunes in order to make them seem real.
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