Rendering Techniques in Computer Graphics

Rendering is the process of visualization image from 2D or 3D with a computer program. Rendering process based on geometry, viewpoint, texture, lighting, and shading information describing the virtual scene that used to give the concept of an artist’s impression of a scene. Rendering is also used to the final process of calculating effects in a video editing program such as giving models and animation their final appearance.

In the case of 3D graphics, scenes can be pre-rendered or generated in real time. Pre-rendering is a slow, computationally intensive process that is typically used for movie creation, where scenes can be generated ahead of time, while real-time rendering is often done for 3D video games and other applications that must dynamically create scenes. 3D hardware accelerators can improve real time rendering performance.

In the sketch, rendering is used, which adds in bitmap textures or procedural textures, lights, bump mapping and relative position to other objects. Several images (frames) must be rendered and stitched together to making an video animation.

In rendering techniques, for tracing every particle of light in a scene is almost impractical and spend amount of time. Therefore, more efficient modeling techniques have emerged:

• Rasterization and scanline rendering

Geometrically projects objects in the scene to an image plane, without advanced optical effects. There are two approachment, pixel-by-pixel (image order) and primitive-by-primitive (object order). In high-level representation of an image necessarily contains elements are referred to as primitives in a different domain from pixels. In a schematic drawing, for instance, line segments and curves might be primitives. In rendering of 3D models, triangles and polygons in space might be primitives. Pixel-by-pixel approach is impractical or too slow, for instance, large areas of the image may be empty of primitives, this approach must pass through them. In rasterization will ignore those areas, this approach is the rendering method by one loop through each of the primitives, determines which pixels in the image it affects, and modifies those pixels accordingly. This method used by all current graphics cards. Rasterization usually becomes an option when interactive rendering is needed, however, the pixel-by-pixel approach can often produce higher-quality images and more flexible.

For the older form of rasterization, entire face (primitive) is rendered by a single colour. It’s more complicated, because we must render the vertices of a face by first and then rendering the pixels of that face as a blending of the vertex colors.

• Ray Casting

Geometry model in ray casting is parsed pixel by pixel, line by line, from the point of view outward, as if casting rays out from the point of view. the color value of the object at the point of intersection may be evaluated using several methods. the simplest method, its color value becomes the value of that pixel. The color may be determined from a texture-map. The more sophisticated method is to modify the colour value by an illumination factor. To reduce artifacts, a number of rays in slightly different directions may be averaged.

This technique is considered quite faster than ray tracing, because geometric rays are traced from the eye of the observer, then tracing is carried out from the object where the light originated from and the object is looking for the light source.

However compared to ray tracing, the images generated with ray casting are not very realistic. Due to the geometric constraints involved in the process, not all shapes can be rendered by ray casting.

• Ray Tracing

Rendering technique by tracing the path of light as pixels in an image plane and reproduces the path that each light ray follows in reverse direction from the eye back to its point of origin. The process will continue to repeat until all pixels are formed. This technique involves reflection, refraction, or shadow effects from points within the scene. Ray tracing also accumulate the color value of the light and the value of the reflection coefficient of the object in determining the color of the depiction on the screen. By using this ray tracing technique, effects such as reflection, refraction, scattering, and chromatic aberration can be obtained.

Often, ray tracing methods are utilized to approximate the solution to the rendering equation by applying Monte Carlo methods to it. Some of the most used methods are path tracing, bidirectional path tracing, or Metropolis light transport, but also semi realistic methods are in use, like Whitted Style Ray Tracing, or hybrids.

• Radiosity

This technique is not usually implemented as a rendering technique, but instead calculates the passage of light as it leaves the light source and illuminates surfaces that usually rendered to the display using one of the other three techniques.

This techniques is a rendering techniques based on detailed analysis of light reflection from diffusion surfaces. This techniques divide field into smaller field to find color details so that the process is slow, but the resulting visualization is neat and smooth. Radiosity is more precisely used for the final result of an object.

Rendering Method

• Hidden Line Rendering

This method is used to represent objects whose surface is covered or blocked by other objects with lines representing the sides of the object, but some lines are not visible because of the surface that blocks them.

• Ray Tracing Rendering

This method produces photorealistic images. The basic concept of this method is to follow the process experienced by a light on its way from the light source to the screen and estimate what kind of color is displayed on the pixel where the light falls. The process will be repeated until all the required pixels are formed. The idea of ​​this method originated from Rene Descartes’s experiment, in which he showed the formation of a rainbow using a glass ball filled with water by resuming the direction of light.

• Shaded Rendering

In this method, the computer is required to perform various calculations both lighting, surface characteristics, shadow casting, etc. This method produces a very realistic image, but the disadvantage is the long rendering time required.

• Wireframe Rendering

In wireframe rendering, an object is formed only visible lines that describe the edges of an object. This method can be done by a computer very quickly, the only drawback is the absence of a surface, so that an object looks transparent. So there is often a misunderstanding between the front and back side of an object.