Attributes

Attributes

Any parameter that affects the way a primitive is to be displayed referred to as an attribute parameter

Line Attributes

1.Line Type:

possible line type attribute include solid lines, dashed lines, dotted lines

2.Line Width

possible line width attribute include thicker line, thinner line and standard line. 3. Line Color

no of colors that can be provided to an output primitives depends upon the display device we used.

4. Pen and brush options

lines generated with pen or brush shapes can be displayed in various widths by changing the size of the mask. These shapes can be stored in a pixel mask that identifies the array of pixel positions that are to be set along the line path

Curve Attribute

Area Fill Attributes

Options of filling a defined region include a choice between a solid color or a patterned fill and choices for the particular colors and patterns.

Basic Fill Styles:

Hollow fill, Solid fill , Patterned fill

Character Attributes:

Text Attributes

A set of characters are affected by a particular attribute.

(Font,size,style,color,alignment,hight,bold,italic,)

Marker Attributes

A particular character is affected by a particular attribute. (marker type, marker precision).

Antialiasing

The distortion (or) deformation of information due to low frequency sampling is called aliasing. The aliasing effect can be reduced by adjusting intensities of pixels along the line to minimize the effect of alising is called antialiasing.

We can improve the appearance of displayed raster lines by applying antialisaing methods that compensate for the under sampling process.

Methods of antialising

1. Increasing Resolution

2. Unweighted area sampling

3. Weighted area sampling

4. Thick line segments

1. Increasing Resolution

The alising effect can be minimized by increasing resolution of the raster display. By increasing resolution and making it twice the original one, the line passes through twice as many column of pixels and therefore has twice as many jags, but each jag is half as large in x and in y direction.

This improvement cause increase in cost of memory, bandwidth of memory and scan-conversion time. So it is a expensive method to reduce the aliasing method.

2. Unweighted area sampling

In general the line drawing algorithm select the pixels which is closer to the true line. In antialsing instead of picking closest pixel, both pixels are high lighted. However their intensity values may differ.

In unweighted area sampling, the intensity of pixel is proportional to the amount

of line area occupied by the pixel. It produces better results than does setting pixels either to full intensity or to zero intensity.

3. Weighted area sampling

In weighted area sampling small area closer to the pixel center has greater

intensity than does one at a greater distance. Thus in weighted area sampling the intensity of the pixel is dependent on the line area occupied and the distance of area from the pixel’s center.

4. Thick line segment

In raster displays it is possible to draw lines with thickness greater than one pixel. To produce a thick line, we have to run two line drawing algorithms in parallel to find the pixels along the line edges, and while stepping along the line we have to turn on all the pixels which lie between the boundaries.