Computer GraphicsComputer GraphicsAn IntroductionAn Introduction

Jimmy LamThe Hong Kong Polytechnic University

AgendaAgenda

Introduction to Computer GraphicsIntroduction to Computer Graphics Computer SystemComputer System Image Specifications (resolution and Image Specifications (resolution and

colour depth)colour depth) Image mode (bit-mapped and vector)Image mode (bit-mapped and vector) Image Colour (RGB, CMYK and Image Colour (RGB, CMYK and

channel)channel) CAD/CAM systemCAD/CAM system

The ComputerThe Computer

CPU – fetches, decodes and executes CPU – fetches, decodes and executes instructions through active RAM instructions through active RAM memorymemory

Storage memoryStorage memory

I/O device – scanner, printer, monitorI/O device – scanner, printer, monitor

Computer Image (1)Computer Image (1)

1. Resolution

– With larger screen you could see larger With larger screen you could see larger number of pixelsnumber of pixels

– The most common display – The most common display – 640 x 480 pixels or 1024 x 756 pixels640 x 480 pixels or 1024 x 756 pixels

– The greater the screen resolution – dpi (dot per The greater the screen resolution – dpi (dot per inch), the clearer the imageinch), the clearer the image

– Standard resolution is 72 dpiStandard resolution is 72 dpi

Computer Image (2)Computer Image (2)

2. Graphic board

– It supports various numbers of bits per It supports various numbers of bits per pixelpixel

– A bit is the smallest amount of binary A bit is the smallest amount of binary information used by the computer and information used by the computer and graphic boards operate on an 8-, 12-, graphic boards operate on an 8-, 12-, 16- or 32-bit-per-pixel system16- or 32-bit-per-pixel system

Computer Image (3)Computer Image (3)

The greater the bit depth the greater the The greater the bit depth the greater the number of colours that can be displayednumber of colours that can be displayed

Standard board is 8-bit for 256 coloursStandard board is 8-bit for 256 colours

16-bit board – 32,76816-bit board – 32,768

24-bit board – 16.7 million24-bit board – 16.7 million

Computer Image (4)Computer Image (4)

3. Scanner

Available in B/W, greyscale and colourAvailable in B/W, greyscale and colour

Transfer artwork, images or founded Transfer artwork, images or founded objects into the computerobjects into the computer

Requires good deal of memory space on Requires good deal of memory space on the hard diskthe hard disk

The higher the resolution of the scan, The higher the resolution of the scan, the more memory is requiredthe more memory is required

If the resolution of scan is equal to If the resolution of scan is equal to the screen resolution, the scale of the screen resolution, the scale of print out would be the same as seen print out would be the same as seen on screenon screen

Basic Image ModesBasic Image Modes

Bitmap (1)Bitmap (1) Computer graphics - 2 main categories: bitmap/ vector. Computer graphics - 2 main categories: bitmap/ vector.

Bitmap images--technically called raster images--use a Bitmap images--technically called raster images--use a grid of colors known as pixels to represent images. grid of colors known as pixels to represent images.

When working with bitmap images, pixels are edited When working with bitmap images, pixels are edited rather than objects or shapes.rather than objects or shapes.

Bitmap images are resolution-Bitmap images are resolution-dependent, contain a fixed number dependent, contain a fixed number of pixelsof pixels

Details could be lost and appear Details could be lost and appear

jagged if scaled on-screen or if jagged if scaled on-screen or if printed at a lower resolutionprinted at a lower resolution

Bitmap (2)

VectorVector

Vector graphics are made up Vector graphics are made up of lines and curves defined by of lines and curves defined by mathematical objects mathematical objects

Vector graphics are resolution-Vector graphics are resolution-independentindependent

Can be scaled to any size and printed Can be scaled to any size and printed at any resolution without losing detail at any resolution without losing detail or clarity.or clarity.

The best choice for representing bold The best choice for representing bold graphics that must retain crisp lines graphics that must retain crisp lines when scaled to various sizes e.g. when scaled to various sizes e.g. logos.logos.

Vector (2)

Bitmap Image Vector Image

QuestionsQuestions

What type of image file (bitmap or What type of image file (bitmap or vector) is normally used to represent vector) is normally used to represent textile fabric (knitted or woven)?textile fabric (knitted or woven)?

For fashion design, what kind of For fashion design, what kind of image file will be used and why?image file will be used and why?

Image ColourImage Colour

What colour images are displayed by What colour images are displayed by computer monitor?computer monitor?

What colour images are printed out What colour images are printed out by computer printer and textile by computer printer and textile printer?printer?

How do you match colour of your How do you match colour of your fabric samples to the computer fabric samples to the computer monitor?monitor?

Colour: GrayscaleColour: Grayscale Grayscale uses tints of black to represent a Grayscale uses tints of black to represent a

design. design.

A brightness value ranging from 0% (white) to A brightness value ranging from 0% (white) to 100% (black). 100% (black).

Images produced using B/W or grayscale Images produced using B/W or grayscale scanners are typically displayed in grayscale.scanners are typically displayed in grayscale.

Convert artwork to high-quality black-and-Convert artwork to high-quality black-and-white artwork.white artwork.

Colour:RGBColour:RGB

Primary colours – Red, Green, Blue, Primary colours – Red, Green, Blue, most widely usedmost widely used

Called additive colors because white is Called additive colors because white is created by adding R, G, and B togethercreated by adding R, G, and B together

Additive colors are used for lighting, Additive colors are used for lighting, television, and computer monitorstelevision, and computer monitors

Colour: CMYKColour: CMYK

Cyan, Magenta, Yellow, and BlackCyan, Magenta, Yellow, and Black

RGB model depends light source to create RGB model depends light source to create color, the CMYK model is based light-color, the CMYK model is based light-absorbing quality of ink printed on paperabsorbing quality of ink printed on paper

Combining pure C, M, and Y pigments Combining pure C, M, and Y pigments resulted in black. So they are called resulted in black. So they are called subtractive colors. Black (K) ink is added subtractive colors. Black (K) ink is added for better shadow densityfor better shadow density

Colour: ChannelsColour: Channels

Channels – image component contain Channels – image component contain pixel information for any given colour pixel information for any given colour – e.g. RGB, CMYK, Grayscale– e.g. RGB, CMYK, Grayscale

Resolution – measurement of Resolution – measurement of fineness of detail, the higher the fineness of detail, the higher the resolution, the finer the detailresolution, the finer the detail

CAD/CAMCAD/CAM

CAM – more process oriented, CAM – more process oriented, concept of time is importantconcept of time is important

CAD defines a part, whereas CAM CAD defines a part, whereas CAM defines a part’s manufacturing defines a part’s manufacturing processes, from raw material to processes, from raw material to finished productfinished product

Can CAD and CAM join as one?Can CAD and CAM join as one? Yes, but…Yes, but…

The differences between the two will The differences between the two will impede their integration, because their impede their integration, because their workflows and final products are so workflows and final products are so differentdifferent

Also because of the nature inherent in how Also because of the nature inherent in how they are usedthey are used

It probably will for the foreseeable futureIt probably will for the foreseeable future

QuestionsQuestions

How can you match colour between How can you match colour between two fabric samples?two fabric samples?

Is it possible to use CAD system to Is it possible to use CAD system to eliminate colour different between eliminate colour different between two fabric samples?two fabric samples?