COMPUTER GRAPHICS AND DISPLAY -MASTER GUIDE

INTRODUCTION:

Computer graphics involves display, manipulation and storage of pictures and experimental data for proper visualization using a computer. It provides methods for producing images and animations (sequence of images). It deals with the hardware as well as software support for generating images. 

The term computer graphics deals with: 

• The representation and manipulation of pictorial data by a computer

• The various technologies used to create and manipulate such pictorial data 

• The images so produced • The study of methods for digitally synthesizing and manipulating visual content

IMAGE AND OBJECTS :

An image is basically representation of a real world object on a computer. It can be an actual picture display, a stored page in a video memory, or a source code generated by a program. Mathematically, an image is a two - dimensional array of data with intensity or a color value at each element of the array. 

Objects are real world entities defined in three – dimensional world coordinates. In computer graphics we deal with both 2D and 3D descriptions of an object. We also study the algorithms and procedures for generation and manipulation of objects and images in computer graphics. 

IMAGE REPRESENTATION:

 Image representation is the approximations of the real world displayed in a computer. A picture in computer graphics is represented as a collection of discrete picture elements termed as pixels. A pixel is the smallest element of picture or object that can be represented on the screen of a device like computer. 

The process of determining the appropriate pixels for representing pictures or object is called rasterization, and the process of representing continuous pictures as graphical object (as a collection of discrete pixel) is called a scan conversion.

 A digital image is a 2D discrete signal. Mathematically, such signals can be represented as functions of two independent variables—for example, a brightness function of two spatial variables, f(x, y) is a 2D array of luminance values, given by

with 0 ≤ f(x, y) ≤ L, and typically L = 255, is the maximum gray level of the image.

RASTER (BITMAP) AND VECTOR – BASED GRAPHICS: 

Computer graphics can be classified into two categories: Raster(composed of pixels) or Bitmap graphics and Vector(composed of paths) graphics. 

Bitmap graphics:

• It is pixel based graphics. 

• The raster system represents an image as a 2D array where the value in the array defines color or gray scale, for the corresponding image.

• The position and color information about the image are stored in pixels arranged in grid pattern.

• Bitmap images are mapped to a grid or an array of pixels 

• The Image size is determined on the basis of image resolution. 

• These images cannot be scaled easily.

• Bitmap images are usually created and edited in photo or paint programs such as Adobe Photoshop 

• Bitmap images are used to represent photorealistic images which involve complex color variations.

The above figure shows a bitmap arrow image in its actual size and magnified image with pixel grid.

 Vector graphics: 

• The images in vector graphics are basically mathematically based images. 
• Vector based images have smooth edges and therefore used to create curves and shapes
•  The vector system relies on quick transformation and fast drawing of the primitive like lines, shapes etc.

• These images are appropriate for precise illustrations but not good for photorealistic images.
•  Vector-based images are usually created and edited in software like CoralDRAW and Adobe Illustrator 
• These images are easily scalable due to their mathematical structure.Figure 1.4(a) and (b) shows a rose image and vector description of leaf of rose. 

The above figure shows a bitmap and vector image of the letter A.

APPLICATIONS OF COMPUTER GRAPHICS 

Computer graphics finds applications in our lives starting from the most basic needs of objects representation to animation and visual effects. The following applications of computer graphics attempt to solve many of our day-to-day problems:

 Digital art: A digital art, most commonly, refers to an art created on a computer in a digital form. A digital art can be purely computer-generated, such as fractals and an algorithmic art or taken from another source like a scanned photograph or image drawn using vector graphics software. 

Special effects: Illusions used in film, television, and entertainment industries to simulate the imagined events in a story are traditionally called special effects (also known as SFX or SPFX). In modern films, special effects are usually used to alter previously-filmed elements by adding, removing, or enhancing objects within the scene.

Visual effects: Visual effects (or VFX, in short) are the term given in which images or film frames are created and manipulated for film and video. Visual effects usually involve the integration of live-action footage with computer-generated imagery or other elements (such as pyrotechnics or model work) in order to create environments or scenarios which look realistic. But visual effects may be dangerous, costly, or simply impossible to capture on a film. 

Video games: Video games find a good place in the gaming and animation industry.

 Computer-aided design: Some of the other areas of applications of computer graphics include computer-aided design (CAD). lhis is used by civil, mechanical, and electronic engineers to build a model of building, bridges, printed circuit board (PCB), etc.

 Medical imaging: It can be used to train new doctors on understanding and experimenting surgery. It is used in molecular biology to study the biological model in genes.