CS- 375 Graphics and Human Computer Interaction

Lecture 1: 12/4/1435

Fundamental Techniques in Graphics

Lecturer: Kawther Abas

2Angel: Interactive Computer Graphics 5E © Addison-Wesley 2009

Computer Graphics

•Computer graphics deals with all aspects of creating images with a computer–Hardware–Software–Applications

3Angel: Interactive Computer Graphics 5E © Addison-Wesley 2009

CRT

Can be used either as a line-drawing device (calligraphic) or to display contents of frame buffer (raster mode)

Computer Graphics

• “Computer graphics refers to using a computer to create or manipulate any kind of picture, image, or diagram.” ,with a graphics editing program– MS Paint– Adobe Photoshop– GIMP– Etc.

Bitmapped Graphics• There are two basic types of graphics:

– Bitmapped and and Vector

• Bitmapped graphics are much more common• Often they are called raster graphics• When you create a bitmapped graphic you are

basically creating a bunch of colored dots• The bitmapped graphic is stored as an array of dots,

or pixels each pixel gets assigned a specific color• The more pixels you have, the more detailed the

image can be

6Angel: Interactive Computer Graphics 5E © Addison-Wesley 2009

Raster Graphics

• Image produced as an array (the raster) of picture elements (pixels) in the frame buffer

bitmap graphics programs

• Some common bitmap graphics programs are:

1. Photoshop

2. Paint Shop Pro

3. GIMP

4. Photo-Paint

5. Graphic Converter

• These are paint programs

Vector Graphics

• Vector graphics are created and manipulated using drawing programs (as opposed to paint programs for bitmapped graphics)

• Instead of using pixels to describe the image, it describes the image using shapes

• Circles– Lines– Curves

• Also has to store the color of these shapes

The programs used with vector graphics

• Some of these programs include:– Corel Draw– Adobe Illustrator– Acrobat

• Most of these programs allow the use of bitmapped images as part of a vector image

Bitmap vs. Vector Images

• Bitmap and vector images are obviously different

• Both have strengths and weaknesses

• They don’t manipulate images in the same way

• They don’t store images in the same way

• The images are edited differently

Bitmap Images

1. Very flexible– Any image can be represented (with enough pixels)

2. Created by scanners, digital cameras, and other similar devices

3. Used most commonly, especially on the web4. Can be displayed directly on your computer

screen if 1 image pixel is the same size as 1 screen pixel

5. Takes a lot of memory– The color of each pixel must be stored– Can be compressed

Vector Images

1. Easy to change parts of the image since each part is stored as a different shape

2. Can manipulate the image smoothly– Rotating, changing color, size, line width, etc.

3. Limited to the shapes the program can handle

4. Typically takes less memory and disk space than a bitmap

5. Must be converted to a bitmap to display

File Formats

• Each way of storing an image is called a file format

Hopefully, you’re familiar with JPEG and GIF file formats .

• You can’t just rename “somepicture.gif” to “somepicture.jpg” and expect to get the desired result– Can’t just rename a .doc file as .ppt and expect a

presentation out of it • Images have to be converted from one file

format to another

Common File Formats

Bitmap Formats• GIF: graphics interchange

format• JPEG: joint photographic

experts group• PNG: portable network

graphic• BMP: Windows bitmap• TIFF: tagged image file

format

Vector Formats• SVG : scalable vector

graphics• EPS: encapsulated

postscript• CMX: Corel meta

exchange• PICT: Macintosh Picture• WMF: Windows metafile

It is an attribute of objects (like texture, shape, smoothness, etc.)•Color is a sensation produced by the human eye and nervous system.

It depends on:

1) spectral characteristics of the light source(s) (e.g., sunlight) illuminating the objects (relative spectral power distribution(s) SPD)

2) spectral properties of objects (reflectance)

3) spectral characteristics of the sensors of the imaging device (e.g., the human eye or a digital camera)

What is color?

• The Two Most Common Color Models:

- RGB model (Red-Green-Blue)

- CMYK model (Cyan-Magenta-Yellow-blacK)

Color Model

* Types of Color model.

1) RGB Color Model:

* Additive color model.

* For computer displays.

* Uses light to display color.

* Colors result from transmitted light.

* Red + Green + Blue = White.

Color Model

* Types of Color model.

2) CMYK Color Model:* Subtractive color model.

* For printed material.

* Uses ink to display color.

* Colors result from reflected light.

* Cyan + Magenta + Yellow = Black.

Color Model

* Types of Color model.