In this chapter, you will learn

By Netbalone - www.netbalone.com

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In this chapter, you will learnIn this chapter, you will learn

– How computer handles graphic objects

– The differences between a bitmap file and a vector file

– The differences among different common graphic file formats


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Number of Bits No. of states1 28

162432

Handling Computer Handling Computer GraphicsGraphics

– Computer Handles data in binary format: 0 or 1 (bit)

28 = 256216 = 65,535

224 = 16,777,216232 = 4,294,967,296


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Bitmap Graphics

• A bitmap graphic is represented by a dot pattern

• Each dot is called a Pixel (picture element)• A pixel has a single color only

Pixel


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To have a better understanding of bitmap graphics, let’s start with the simplest type of bitmap picture - Monochrome (i.e. B&W) Bitmap


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• A pixel can be Black or white (2 states)• So, 1 bit can be used to code the color

B&W Bitmap Graphics

111111111111111111111111110001111111111101111111111111000111111111111000111111111111011111111111110000111111111111001111111111111011111111111101111111111111

1 - White0 - Black

1 - White0 - Black


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B&W Bitmap Graphics

• Therefore, a full screen (800 x 600) monochrome bitmap picture requires storage of

(800 x 600 x 1) bits= 480000 bits= 60000 bytes= 58.59 kB


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Grayscale Bitmap Graphics

• Grayscale graphics are created by using shades of gray• 8 levels of grayscale

000 001 010 011 100 101 110 111

How many bits should be used to How many bits should be used to represent the gray colors of each represent the gray colors of each pixel?pixel?

3 bits3 bits


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How many bits are necessary to represent 256 colors in each pixel?

8 bits8 bits


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• How many bits are necessary to represent a 800 x 600 graphic of 256 colors?

Question:Question:

Number of bits used= 800 x 600 x 8 bits= 3,840,000 bits

(Storage required: 468.75 kB)

The larger the resolution and the no. of colors, the more storage spaces are required to hold the graphic

The larger the resolution and the no. of colors, the more storage spaces are required to hold the graphic


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Vector Graphics

• A vector graphic is divided into objects

• Each object is defined by the method of drawing it

This picture contains 3 objects:a line, a circle and a rectangle

This picture contains 3 objects:a line, a circle and a rectangle


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How to draw the circle?

• The circle is represented by a mathematical formula:

Circle(50,100,150,black,1,green)Circle(50,100,150,black,1,green)

Radius

Center

Line colorLine thickness

Fill color

A few bits is enough to save the properties of this circle!A few bits is enough to save the properties of this circle!


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Graphics:• It requires less storage space• When a vector graphic is enlarged, it remains intact (no

distortion)

Enlarging a Vector Graphic

Enlarging a Bitmap Graphic

The line is as smooth as before

The line thickened & saw-tooth resulted


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Common Graphic File Format

Bitmap (.bmp) - a common graphic file format;can be read by almost all programs

Gif (.gif) - a compressed bitmap file format. It can support up to 256 colors

Jpeg (.jpg) - a lossy compressed bitmap file format. But it can support up to 16.7 million colors

(because it applies lossy compression, some of the details is lost!)


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Jpeg Format (5kB)Gif Format (26kB)


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Comparison Table:

Fileformat

File Size Maximum numberof colours support

Quality of image Remarks

Bmp Large(uncompressed bitmap)

256 Good seldom used due to itslarge file size.

Gif Small(compressed bitmap)

256 Good commonly used

Jpg smallest (Lossycompression)

16.7 million varied, best fortrue colour photo

File size and quality offile can be controlled,Used in most digital

cameraVector Small Depends on

different softwareCompatible to a

few software onlyProprietary format


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8-bit color means 28 = 256 different colors

16-bit (High) color means 216 = 65535 different colors

24-bit (True) color means 224 = 16777216 different colors

How colors are represented?

The number of bits used to represent colors is called color depth.The number of bits used to represent colors is called color depth.


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RGB Color Scheme

• All colors are made up of 3 primary colors of light: Red (R), Green (G) and Blue (B)

• Different intensities of red, green and blue can mix up different colors

• In computer, 8 bits are used to represent 256 levels of each of these primary colors

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Example:

• RGB(255,0,0) = Red

• RGB(0,255,0) = Green

• RGB(0,0,255) =

• RGB(0,0,0) =

• RGB(255,255,255) =

• RGB(255,0,255) =

Http://www.phy.ntnu.edu.tw/~hwang/image/rgbColor.html

Blue

Black

White

Magenta

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CMYK Color Scheme

• For printing, publisher will find CMYK scheme more suitable for ink used.

• CMYK represents 4 colors: Cyan, Magenta, Yellow and blacK.

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In this chapter, you will learn