raster graphics

Raster graphics

Raster graphics

Colour depth

0 1

1 bit pr pixel = 2 combinations (21):

2 bits pr pixel = 4 combinations (22):

00 01 10 11

4 bits pr pixel = 16 combinations(24)8 bits pr pixel = 256 combinations(28)16 bits pr pixel = 65636 combinations(216)24 bits pr pixel =16777216 combinations(224)

Colour depth

1 bpp = 21 = 2 colours

2 bpp = 22 = 4 colours

4 bpp = 24 = 16 colours

8 bpp = 28 = 256 colours

16 bpp = 216 = 65.536 colours

24 bpp = 224= 16.777.216 colours

Colour depth

Filfe formats

• TIF (Tagged Image File Format) 1-32 bit

• BMP (Windows Bitmap) 8-24 bit

• TGA (Targa) 24-32 bit

• JPG (JPEG – Joint Photographics Expert Group) 8-24 bit

• GIF (Graphics Interchange Format) 1-8 bit

• PNG (Portable Network Graphics) 4-24 bit

F.ex:

Gif-format

• Max 256 colours

• Good for logos, line drawings, buttons

• May be transparent

• May be animated

• Use LZW compression

Gif-format palette

System paletteGoes on 256-colours screens. ‘Uses ‘dithering’

Optimized paletteScreen set to more than 256 colours

Jpg-formatet

• 24 bits colour depth, ie 16.7 million colours(or 8-bit grey scale)

• Good for photos

• Extreme compression possible

Jpg compression

766 x 782 pixels, 24 bitTIF no compression1720 KB

766 x 782 pixels, 24 bitJPG compression 25104 KB

Jpg compression

• Compression factor 1-99

250x200 pixels, 24 bitKompression 15

250x200 pixels, 24 bitKompression 99

11,5 kb 1,7 kb

Jpg / gif …photos

jpg, 11,5 kb gif, 22,4 kb

200x250 pixels 200x250 pixels

Jpg / gif …drawing

gif, 6,08 kb

jpg, 5,5 kb

Anti aliasing

Digitalization

Analog(photo)

Digitalization

(f.x. Scanning)

Digital(Raster image)

Digitalization

Flatbed scanner

Lamp

Photo cells

Image

Direction of scan

Scanner head

Data for computer

Digitalization

Digital camera

CCD chipLens

light

Data forMemory

Scanning - DPI

• DPI = Dots Per Inch –

• Computer screen = 72 DPI – 10x10 cm output = 288 x 288 pixels (72 / 2,5 x 10)

• Standard laser print = 600 DPI– 10x10 cm output = 2400 x 2400 pixels (600 / 2,5 x 10)