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Computer Graphics Techniques and Applications Chapter 1 - Graphics Fundamentals Dr Brett Stevens e-mail: [email protected] phone: 023 9284 5482 address: West Wing, Eldon Building notes: http://techfaculty.port.ac.uk/cgtap 16 Hours -

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computer graphics techniques and applications

Computer Graphics Techniques and Applications

Chapter 1 - Graphics Fundamentals

Dr Brett Stevens

e-mail: [email protected]

phone: 023 9284 5482

address: West Wing, Eldon Building

notes: http://techfaculty.port.ac.uk/cgtap

slide2

16 Hours

-

Lectures to take place in Mercantile House, Room 5.02.

This will include computer graphics theory and discussion of relevant social and technical issues.

20 Hours

-

Practicals to take place in Mercantile House, Room 3.04b.

This will include access to graphics production facilities for formal tutorial sessions and continuing project work.

1 Hour

-

Exam, which will constitute 60% of your grade.

This will be an individual, open book, computer based test.

Ongoing

-

Coursework, which will constitute 40% of your grade.

There will also be an assessed, continuous practical component that will help develop practical and problem solving skills.

slide3

Unit Web Site

Notes:

http://techfaculty.port.ac.uk/cgtap/index.htm

Books:

http://techfaculty.port.ac.uk/cgtap/booklist.htm

Coursework:

http://techfaculty.port.ac.uk/cgtap/assessment.htm

2d vs 3d graphics
2D vs 3D Graphics
  • Coordinate Systems
    • Cartesian Coordinates.
      • Axis, (pl axes).
      • Origin.
  • 2D has “x axis” and a “y axis”
  • 3D has “x axis”, “y axis” and a “z axis”
piet mondrian circa early c20th
Piet Mondrian (circa EarlyC20th)

Red, Yellow and Blue 1921 (oil on canvas)

depth cues

Physiological

Pictorial

Monoscopic

Motion Parallax

Accommodation

Occlusion

Relative Height

Relative Size (Requires Expected Size)

Linear Perspective

Foreshortening

Texture Gradients

Shading and Shadows

Aerial Perspective

Relative Brightness

Stereoscopic

Convergence

Stereopsis

Depth Cues
slide8

Leonardo da Vinci

The Last Supper, 1498

slide10

2D Graphics

  • Information stored within that framework can be subdivided into two categories.
    • Bitmapped (or raster) graphics created with paint programs, such as Corel’s Photopaint or Adobe’s Photoshop.
    • Vector graphics created and manipulated with a draw programs, such as Coreldraw or Adobe’s Illustrator
slide11

2D - Bitmapped Graphics

Bitmapped (Raster) graphics use a 2D array of points (pixels).

Like Pointalism.

Gray Weather by

George Seurat (1859-1891)

slide12

Bitmapped Graphics

  • The number of pixels used in a bitmap is its spatial resolution (e.g. 1024x768).
  • The number of bits (i.e. 0s and 1s) used to represent a colour is known as the bit depth or colour resolution. e.g. 24 bit.
    • This is not the number of colours itself.
bit depths and colours
Bit Depths and Colours
  • 1 bit = 2 Colours (Actually Black or White)
  • 4 bit = 16 Colours
  • 8 bit = 256 Colours (GIFs)
  • 24 bit = 16,777,216 Colours (JPGs)
  • 48 bit = 281,474,979,710,656 (PNGs)
file sizes and bit depths
File Sizes and Bit Depths

File size of a bitmap is

(Resolution x Bit depth + file overhead) / 8 = Size in Bytes

slide16

Greyscale to Black and White.

Grey Scale

Threshold

Dithered

slide17

Dithering an Image.

What is the theoretical file size of the image before and after dithering?

Then create the display matrix again but with the dither matrix, 3,6,9,12 (ordered from the top left to the bottom right) and work through the exercise again. What do you notice.??

slide18

Aliased and Anti-Aliased Images.

To display a ‘continuous’ line it must be divided amongst discrete pixels. This can lead to the line looking jagged or aliased.

slide19

Perfect and Sub-Pixel Sampling

This requires enough bit depth to support the ‘extra’ colours

slide20

Bitmap Compression

  • The file size for storing bitmapped graphics can be very large.
  • codecs specify how a file should be COmpressed and DECompressed.
    • Lossless compression (gif, png)
    • Lossey compression (jpg)
file sizes and bit depths21
File Sizes and Bit Depths

(Spatial resolution * Colour resolution) + file overhead) / 8 compression ratio

= File Size in Bytes (divide this by 1024 to get the size in KB).

All these factors are dictated by the file type …

slide22

2D Vector Graphics

Vector graphics use a mathematical representation.

Primitives are the basic shapes from which drawings are constructed.

The term refers to geometry, shape and position.

The primitives have attributes, which specify additional display information, such as the colour of an element, its orientation

slide23

Michelangelo Buonarroti

Pieta 1498-99 Marble. Basilica of St Peter, Vatican

slide24

3D - Volume or Surface Graphics

  • Volume uses a 3D array of points (voxels). Like bitmaps.
  • Surface graphics use a description of an object’s boundaries (polygons). Like vectors.
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