Date post: | 03-Jan-2016 |
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Upload: | devin-parks |
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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)