Computer Graphics: Question Set – 04

Explain text mode and graphics mode.

Text Mode:

In text mode, the screen is internally rendered as text rather than pixels. The screen is divided into a rectangular grid (cell or termed box), with each cell capable of bolding only one character.

Text mode with 25 rows and 80 columns of characters is supported by all video standards. Text mode uses mono-space typefaces, which means that each character is the same width on the screen. So that the output can be appropriately aligned.

Text mode screen manipulation is faster than its counter part and requires less memory.

Text mode
Graphics mode

Graphics Mode:

It is a computer display mode that uses pixels to create an image. The screen is internally represented as a grid of pixels in graphics mode. The smallest addressable entity on the screen is the pixel.

Pixels are used to represent everything, including characters. More smooth shapes and typefaces are supported in Graphics mode. In text mode, graphical objects such as a circle, line, triangle, and so on cannot be displayed.

The application programmer can switch between text and graphical mode as needed.

Enlist supported display mode for various adapters

Adapter AcronymFull formResolutionAspect RatioColor Supported
SXGASuper Extended Graphics Array1280 x 10245:4224
SVGASuper Video Graphics Array800 x 6004:316
VGAVideo Graphics Array640 x 4804:316
MCGAMulti-Color Graphics Adapter320 x 200,
640 x 480
4:3
4:3
256
2
EGAEnhanced Graphics Adapter640 x 350,
640 x 200,
320 x 200
4:3
4:3
4:3
16
16
16
Hercules720 x 3484:32
CGAColor Graphics Adapter640 x 200,
320 x 200,
160 x 200
4:3
4:3
4:3
2
4
16

Explain the Rasterization process in graphics pipeline

Tessellation is a procedure that converts each thing into triangles. Later on, triangles are broken down into the smallest parts known as pixels. Through the process of rasterization, the entire continuous scene is drawn in a discrete form on a monitor.

The pixel’s color is determined by the light source, viewing direction, object material property, and so on. Finally, the result is combined and shown on the monitor screen.

Rasterization process in graphics pipeline
Rasterization process in graphics pipeline

Compare Bitmap Graphics and Vector Graphics

Sr. No.Bitmap GraphicsVector Graphics
1.Represents scene using pixels.Represents scene using mathematical formulas.
2.Bitmap graphics is resolution dependent.Vector graphics is resolution independent.
3.Bitmap images scale poorly.Vector images are good at scaling.
4.Good for representing realistic scenes.Good for the images having large area of constant colors.
5.On scaling, border starts appearing zigzag.Sustains the change in scale.
6.Such images are suited for web applications.Not suited for web applications.
7.Requires more memory compared to vector graphics.Requires less memory compared to bitmap images.
8.Modification is difficult.Modification is easier.
9.Conversion from bitmap to vector graphics is difficult.Conversion from vector to bitmap graphics is easy.
10.Examples :  JPEG, GIF, BMP etc.Examples : True type fonts, Postscripts, Logo etc.

Define: Rasterization

To keep the scene on the screen, it is necessary to constantly redrawing all of the pixels on the monitor screen. This is known as refreshing, and such a display system is known as refresh CRT.

Define Persistence rate. What is the effect of it on display?

The persistence rate specifies how long pixels continue to emit light after the CRT beam has been removed.

Persistence of phosphor refers to the amount of time it takes for emitted light to degrade to one-tenth of its original intensity.

Because phosphor has a lower persistence rate, higher refresh rates are required to keep a picture on the screen without flickering.

What is aspect ratio?

Another feature of a video display is the aspect ratio, which is the ratio of the number of vertical pixels required to draw the same length of a line in both directions.

A 9/16 aspect ratio means that a vertical line drawn with 9 points has the same length as a horizontal line drawn with 16 points.

The distance between two vertical pixels is generally greater than the distance between two horizontal pixels.

Screens with different aspect ratio

Explain horizontal and vertical retrace.

When each scan line (row) is completed, the electron guns are shut off and relocated to the beginning pixel of the following scan line. This horizontal movement is referred to as horizontal retrace. Electron guns are transferred to the first pixel of the first row after reaching the last pixel of the screen. Vertical retrace refers to the vertical movement of electron weapons.

Rasterization - interlaced display
Retrace

What is random scan display?

The electron beam in a random scan system exactly follows the section of the screen where the image is to be displayed. Because the image is recorded in terms of line drawing commands rather than individual pixels, it is also known as vector displays, stroke-writing displays, or calligraphic displays.

Scholarly Reading: Aspect Ratio

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