Intro To Media Tech: Lecture 3

Front 1

Bitmap images

Back 1

store images as a list of numbers, one per pixel

.bmp

Front 2

Advantages

Back 2

Quality

Front 3

Disadvantages

Back 3

Size

Front 4

Calculating Size of Bitmap

Back 4

(W*H*D/8,000,000)

Front 5

Compression

Back 5

Lossy and Lossless

Front 6

Lossy

Back 6

reduces size by discarding data

Front 7

Advantage

Back 7

Large reduction in size vs. lossless

Front 8

Disadvantage

Back 8

Can reduce quality

Front 9

reducing colour depth

Back 9

reducing colour depth can cause posterizing

Front 10

avoiding this by using a colour palette

Back 10

indexing colour: only stores most common colours in image

index included at start of file

Front 11

chrome sub sampling (lossy)

Back 11

120 million rod cells sense luminance (brightness)

6 million cones sense chromo (colour)

Front 12

Subsampling

Back 12

store Y(luminance)
B-Y

R-Y
this is called the YCbCr colour space

Front 13

Luminance

Back 13

Y=R+G+B

R=(R-Y)+Y
B=(B-Y)+Y

G=Y-R-B

Front 14

Subsampling to compress

Back 14

break image into 2x2 blocks

store luminance for each pixel

average

Front 15

JPEG

Back 15

Joint Photographic Experts Groups uses Chroma Subsampling

Front 16

compression artefacts

Back 16

sub sampling causes articling round sharp edges, photos look ok; logos and diagrams can look poor though

Front 17

lossless

Back 17

reduces size without discarding data ; less effective than lossy at reducing file size

Front 18

Run Length Encoding

Back 18

reduces file size by removing runs of repeated data

Front 19

WWWWWBBBWWWWWBWWWWWWWWW

Back 19

5W3B5W1B9W

Front 20

Supported file formats that use lossless

Back 20

TIFF (Tagged Image File Format) < uses RLE

PNG (Portable Network Graphics)

GIF ( Graphics Interchange Format)

Front 21

Vector Images

Back 21

Geometrical Primitives: Points, Lines, Curves and Polygons
These primitives are called objects

Front 22

Rendering

Back 22

Vector images must be rendered or rasterized at display time which is computationally expensive

Front 23

scaling

Back 23

they can be scaled to any size without any loss of quality and are often far smaller than their bitmap equivalent

Front 24

common uses

Back 24

drawing

charts and graphs

fonts

.svg is part of html5