Binary Images - RIT

[Pages:45]Binary Images

u The simplest digital images are binary images. Binary images contain only one bit per pixel, so they can only represent two gray values. For example;

0 = black 1 = white

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0

Computer Memory & Storage

u If we want an image that has more than two gray levels, we have to increase the number of `bits per pixel'

binary: just white or black

grayscale: many shades of gray

Computer Memory & Storage

1 bit pixel

0 1 2 gray levels

2 bits pixel

0 0 0 1 1 0 1 1 2x2 = 4 gray levels

Computer Memory & Storage

0 0 0 0 0 1 0 1 0 3 bits 0 1 1 pixel 1 0 0 1 0 1 1 1 0 1 1 1 2x2x2 = 8 gray levels

Computer Memory & Storage

u We started to look at the bits as tokens to represent different values, but we ended up with a binary counting system.

u The largest number we can count to (and the number of different gray levels we can have) depends on how many bits we use.

000 = 0 001 = 1 010 = 2 011 = 3 100 = 4 101 = 5 110 = 6 111 = 7 ... = .

Grayscale images

u To get more than two gray values, we need a code with more than one bit per pixel.

1 bit 0 1

(2 values)

2 bits 00 01 10 11

(4 values)

3 bits 000 001 010 011 100 101 110 111

(8 values)

Binary Arithmetic

u In binary arithmetic, we can only count from 0 to 1 before we have to `carry'

u To increase the number of different values that can be represented with a binary number, (and the number of gray levels in a digital image) we have to increase the number of bits

binary

0 1 10 11 100 101 110 111 1000 1001 1010 1011 1100 1101 1110 1111 10000

...

decimal

0

1 1 bit

2

3 2 bits

4 5 6

7 3 bits

8 9 10 11 12 13 14

15 4 bits

16

...

Computer Memory & Storage

3 bits/pixel: 8 gray levels 000 111 (0 7)

4 bits/pixel: 16 gray levels 0000 1111 (0 15)

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