Unit 54 Digital Graphics

JPEG:

This is the right format for those photo images which must be very small files, for example, for web sites or for email .JPG is often used on digital camera memory cards. The JPG format is best for colour photos. But if your page doesn't have a solid background then the JPEG may not float on top of the background very seamlessly.

Raster:

In computer graphics, a raster graphics image is a dot matrix data structure representing a generally rectangular grid of pixels, or points of colour, viewable via a monitor, paper, or other display medium. Raster images are stored in image files with varying formats.

Advantages:

The geographic location of each cell is implied by its position in the cell matrix. Accordingly, other than an origin point, e.g. bottom left corner, no geographic coordinates are stored.

Due to the nature of the data storage technique data analysis is usually easy to program and quick to perform.

The inherent nature of raster maps, e.g. one attribute maps, is ideally suited for mathematical modelling and quantitative analysis.

Discrete data, e.g. forestry stands, is accommodated equally well as continuous data, e.g. elevation data, and facilitates the integrating of the two data types.

Disadvantages:

The cell size determines the resolution at which the data is represented. It is especially difficult to adequately represent linear features depending on the cell

resolution. Accordingly, network linkages are difficult to establish. Since most input data is in vector form, data must undergo vector-to-raster

conversion. Besides increased processing requirements this may introduce data integrity concerns due to generalization and choice of inappropriate cell size.

Vector:

Vector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygons - all of which are based on mathematical expressions - to represent images in computer graphics. Vector graphics are based on vectors (also called paths), which lead through locations called control points or nodes.

Advantages:

The important point of vector graphics is the power of scalability. If you try to enlarge the pixel based image, it only enlarge the size of the squares making up the image area and pixel based image will be jagged. If you consider the vector image, it will remain in its best quality.

Data can be represented in original resolution without generalization. In some data like hard copy maps, no data conversion is needed.

Disadvantages:

The drawing image containing trapping information can only be scaled up to 20% larger or smaller.

Thin lines in vector images may disappear if we reduce the size too much. Photographs cannot be taken as vector images. It must be drawn by the artist, and

must be editing in software like adobe illustrator.

Tiff:

The ability to store image data in a lossless format makes a TIFF file a useful image archive, because, unlike standard JPEG files, a TIFF file using lossless compression (or none) may be edited and re-saved without losing image quality. This is not the case when using the TIFF as a container holding compressed JPEG.