Rasterization (Scan Conversion)

Rasterization (Scan Conversion)

The process of representing continuous graphics object as a collection of discrete pixels by identifying their locations and setting them on is called Scan Conversion. The process of determining which pixels will provide the best approximation to the desired line is properly known as rasterization.

Other definition:

• It is the responsibility of graphics system or the application program to convert each  primitive from its geometric definition into  a set of pixels that make up the primitive in  image space. This conversion task is  generally referred to as a scan conversion  or rasterization.
• In case of line, it can be possible that any pixel may have any floating value like (2.7,5) which will not be considered by the  system.
• Therefore, the process of making these coordinate according to system’s assumption i.e (3,5) to plot the pixel is scan  conversion.

Characteristics

• Convert high-level geometry description to pixel colors in the frame buffer
• Example: given vertex x,y coordinates determine pixel colors to draw line
• Two ways to create an image:
• Scan existing photograph
• Procedural compute values (rendering)

Viewport Transformation -> Rendering -> Rasterization -> Display

• A fundamental computer graphics function
• Determine the pixels’ colors, illuminations, textures, etc.
• Implemented by graphics hardware
• Rasterization algorithms –
• Lines
• Circles
• Triangles
• Polygons
• Drawing lines on the screen
• Manipulating pixel maps (pixmaps): copying, scaling, rotating, etc
• Compositing images, defining and modifying regions
• Drawing and filling polygons
• Previously beginning(GL_POLYGON), etc
• Aliasing and anti aliasing methods.

 

Points to be remember for Scan Conversion

All the objects should be drawn with  constant brightness and Object should be independent of length &  orientation.

Scan Conversion Advantages:

1. It can be used for many different aspects of picture processing, video projectors, TV, cinema equipment, video capture cards, LCD monitors, standard and HDTV televisions, and radar displays.
2. It can be made easily using some high speed integrated circuits as a circuit board.

Scan Conversion Disadvantages

1. The process can be applied using only integrated circuits in LSI and VLSI scales.
2. In digital conversion method first the analog video signal has to be converted to digital data.