جامعة بابل | University of Babylon



introduction

Computer graphics is concerned with all aspects of producing pictures or images using a computer. The field began humbly almost 50 years ago, with the display of a few lines on a cathode-ray tube (CRT); now, we can create images by computer that are indistinguishable from photographs of real objects.

Computer graphics provides a set of tools to create pictures and to interact with them in natural ways. The tools consist of both hardware and software, and together they permit programmers to fashion programs with a strong graphics capability. Data are presented visually through shapes, colors, and texture rather than by tables of numbers. Words and numbers are replaced whenever possible by pictures, because the eye- brain system is better at recognizing and interpreting visual representations. With interactive graphics a person instructs the computer

using natural hand movements, such as pointing and drawing.

Cathode Ray Tubes (CRTs):

Contains a filament that, when heated, emits a stream of electrons are focused with an electromagnet into a sharp beam and directed to a specific point of the face of the picture tube. The front surface of the picture tube is coated with small phospher dots When the beam hits a phospher dot it glows with a brightness relative to the strength of the beam and how long it is hit

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How might one measure CRT capabilities?

• Size of tube

• Brightness of phosphers vs. darkness of tube

• Speed of electron gun

• Width of electron beam

• Pixels?

Terms and Concepts :

Here are a few informal definitions of the graphics field :

Image processing: (more precisely, digital image processing) is the field that deals with methods, techniques, and algorithms for image manipulation, enhancement, and interpolation.

Computer graphics: is the field concerned with the generation, manipulation, and storage of digital graphical data. This includes still images (two- and three-dimensional), animated graphics, and interactive images (virtual reality). In fact, most digital data that is not text, software, or audio, is graphics data.

Computer Graphics vs. Image Processing

In computer graphics, a computer is used to create a picture. Image processing, on the other hand applies techniques to modify or interpret existing pictures

A pixel: (from picture element) is the smallest unit of a digital image. In the computer, a pixel is represented by its color code, which is either a gray scale value or the three components of a color. We tend to think of a pixel as a small dot, circular or square.

(PIX [picture] Element) The fundamental display element of an electronic screen or bitmapped image. Screen resolution is rated by the number of horizontal and vertical pixels; for example, 1024x768 means 1,024 pixels are displayed in each row, and there are 768 rows (lines). Likewise, bitmapped images are sized in pixels: a 350x250 image has 350 pixels across and 250 down.

Pixel Structures

In storage, pixels are made up of one or more bits. The greater this "bit depth," the more shades or colors can be represented. The most economical system is monochrome, which uses one bit per pixel (on/off). Gray scale and color typically use from 8 to 24 bits per pixel, providing from 16 to 16 million colors.

Displaying the Pixel

On a display screen, pixels are either phosphor or liquid crystal elements. For monochrome, the element is either energized fully or not. For gray scale, the pixel is energized with different intensities, creating a range from light to dark. For color displays, the red, green and blue sub pixels are each energized to a particular intensity, and the combination of the three-color intensities creates the perceived color to the eye.

Raster Graphics

• A raster is defined by pixels. A pixel is the smallest display element that makes up the images seen on a computer monitor or television. In raster images, the more pixels an image contains, the higher its resolution. For example, in a raster image a square is drawn as a grid of pixels (dots) and each of those pixels will have a specific color value. A line is made up of a row of pixels with each pixel having a color value, and you work with this line by working with the group of pixels that makes up the line, not as a single object as you would in a vector file. Programs such as Photoshop, PaintShop, and PhotoPaint all work with pixels (raster images). A raster image is resolution-dependant because it contains a fixed number of pixels that are used to create the image. Since there is a fixed and limited number of pixels, a raster image will lose quality if enlarged beyond that number of pixels as the computer will have to 'make up' the missing information. This is usually the cause of the image becoming fuzzy or "steppy".

Vector Graphics

Vector-based designs produce the most clear and precise graphics possible. They use mathematically-defined areas to produce shapes, lines and curves. These graphic formats are created by using professional graphic design programs such as Adobe Illustrator. Because vector-based images are not made up of a specific number of dots, they can be scaled to a larger size and not lose any image quality. If you blow up a raster graphic, it will look blocky, or "pixelated." When you blow up a vector graphic, the edges of each object within the graphic stay smooth and clean. This makes vector graphics ideal for logos, which can be small enough to appear on a business card, but can also be scaled to fill a billboard. Common types of vector graphics include Adobe Illustrator, Macromedia Freehand, and EPS files. Many Flash animations also use vector graphics, since they scale better and typically take up less space than bitmap images.

What is the difference between vector and raster graphics?

 The difference between vector and raster graphics is that raster graphics are composed of pixels, while vector graphics are composed of paths. A raster graphic, such as a gif or jpeg, is an array of pixels of various colors, which together form an image. A vector graphic, such as an .eps file or Adobe Illustrator? file, is composed of paths, or lines, that are either straight or curved. The data file for a vector image contains the points where the paths start and end, how much the paths curve, and the colors that either border or fill the paths. Because vector graphics are not made of pixels, the images can be scaled to be very large without losing quality. Raster graphics, on the other hand, become "blocky," since each pixel increases in size as the image is made larger. This is why logos and other designs are typically created in vector format -- the quality will look the same on a business card as it will on a billboard.

Is it possible to convert a raster graphic into a vector graphic?

Answer: A raster graphic, which is made up of a specific number of pixels cannot be translated into a vector graphic, an image made up of paths. That being said, some programs like Macromedia Flash can create paths out of raster graphics so that they can be manipulated as vector images. This conversion typically reduces the image's size significantly, but different areas of the image are approximated, giving the image a stained-glass look.

While it is possible to create a vector image (i.e. an EPS file) from a raster graphic (i.e. a JPEG image), an exact conversion is not possible. Because of the approximations made in the conversion process, a scaled up vector version of an original raster graphic would most likely look worse than just scaling the raster graphic itself.

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1.3 Applications of computer graphics

•Entertainment

• Computer-aided design

• Scientific visualization

• Training

• Education

• E-commerce

• Computer art

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Computer graphics

3nd stage

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College of sciences for women ((())) Dept. of computer sciences

Year 2014-2015

Lec. (1)

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