Computer Graphics: Question Set – 02

Computer Graphics: Question Set – 02

What do you mean by Resolution in Computer Graphics? Explain its effect with diagram.

Resolution in computer graphics refers to the maximum number of pixels that can be displayed on a monitor screen without overlap. High-quality devices typically have a resolution of 1280 by 1024. High-resolution systems are sometimes known as high-definition systems.

The resolution of images on a monitor screen describes them. An image with a resolution of 800 x 600 has 800 pixels in each row and 600 pixels in each column. The image has resolution of 800 x 600 = 4,800,000 pixels.

As the resolution lowers, fewer samples are collected, and image quality deteriorates. Figure shows an image with resolutions of 256 x 256, 64 x 64, and 16 x 16 pixels.

Resolution in computer graphics
Effect of resolution on image quality

Define basic elements of computer graphics.

Computer graphics elements include animation, interaction, rendering, and modeling.

  • Animation is the simulation of temporal changes in the environment. It is commonly utilized in movies, advertising, and education.
  • Interaction is the process of generating responses to the system’s external inputs.
  • Rendering is the process of creating an image from a 2D or 3D model.
  • Modelling/Geometry is the process of creating a mathematical representation of a three-dimensional surface or object.

How real world object is converted to image?

Objects are physical entities that represent actual objects. Objects can be natural, such as flowers, clouds, mountains, and trees, or manufactured, such as a car, cell phone, book, ball, and so on. A three-dimensional coordinate system is used to represent objects. Computer graphics is concerned with the representation of real-world objects on a computer screen.

An image is a representation of real-world items on a digital display device. Objects in the real world are continuous, with a smooth boundary. They are discretized when mapped on a monitor screen and frequently have zigzag boundaries due to the grid layout of the monitor screen.

Object representation on screen
Object representation on screen

Image is formally a two-dimensional array of pixels. A pixel is an image’s smallest addressable unit. Image is defined mathematically as a function of its spatial coordinates (x, y). Where (x, y) is the pixel position in the image and function f(x, y) is the intensity or color at that place.

The diagram demonstrates how continuous shapes are changed to discrete entities while being turned into a digital image or mapped on a monitor screen.

What is Pixel? How it helps representing shapes on screen?

The pixel, as previously stated, is the smallest addressable unit of an image. It is also referred as as pel or image element. Because real-world objects are continuous in nature, they have an endless number of samples.

Only finite samples are taken into account when they are transformed into a picture and presented on the monitor screen. At the end of the day, the item on the computer screen is a collection of pixels.

The monitor screen, like the digital image, is organized into a grid with n rows and m columns. Each cell on this grid is also known as a pixel. Each grey/black cell in represents one pixel.

Pixel wise representation of image
Pixel wise representation of image

We can obtain a better idea of the pixel by zooming in on the image. In Figure each square represents one pixel.

The pixel value for a grayscale image ranges from 0 to 255, where 0 represents black and 255 represents white. The grey colours with varied intensities are represented by the in-between range.

Each pixel in a color image is a triplet of color (R, G, B) consisting of a proportion of red, green, and blue color. The final color of the pixel on the monitor screen is determined by the combination of these three components. Each component’s value ranges from 0 to 255, resulting in 255 x 255 x 255 = about 17 million distinct color tones.

Define frame buffer. What is the role of frame buffer in display?

The screen image can be thought of as a two-dimensional grid of pixels. The picture is shown by a raster system by drawing pixels in a row by row fashion from left to right. The image definition is saved in a memory known as the refresh buffer or frame buffer.

The scene to be presented is initially loaded into the frame buffer as intensity values. The frame buffer should ideally be the same size as the screen resolution. The intensity value from the frame buffer’s top left location is obtained and painted at a top-left spot on the screen. Soon after, the second pixel of the same row is painted, and the procedure is repeated.

Frame buffers in raster displays hold individual pixels of the scene, whereas frame buffers in random scan displays store commands for rendering the scene.

Resolution in computer graphics refers to number of pixels, where as frame buffer refers to memory to hold the information for those pixels

Compute the memory requirement of the frame buffer for the system having resolution 1280 x 1280 and supports 24 bits per pixel.

Number of pixel = 1280 x 1280 = 16, 38, 400

Number of bits = Number of pixels x Number of bits/pixel

=   16, 38, 400 x 24

=   3, 93, 21, 600 bits

=   39321600 / 8 = 49,15,200 Bytes  (∵ 1 Byte = 8 bits)

=   49,15,200 / 1024 = 4800 KB          (∵  1 KB = 1024 Bytes)

=   4800 / 1024 = 4.69 MB                   (∵  1 MB = 1024 KB)

Thus, the system having screen resolution 1280 x 1280 and supporting 24 bits per pixel require 4.69 MB of memory for the frame / refresh .

Define terms: Bitmap and Pixmap

If the refresh buffer employs one bit per pixel, it is referred to as a bitmap. If it employs multiple bits per pixel, it is referred to as pixmap.

A bitmap is used in a bi-level system, whereas a pixmap is used in a multi-color system.

An additional alpha channel is sometimes preserved to modify the transparency of a pixel.

Additional Reading: Bitmap and Pixmap

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