skills: none concepts: an image representation code, the number of bits in a code, the amount of...

Skills: noneConcepts: an image representation code, the number of bits in a code, the amount of information in an image

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Encoding images

Where does this topic fit?

• Internet concepts– Applications– Technology– Implications

• Internet skills– Application development– Content creation– User skills

Encoding image data

Data type Decade

Numeric 1950s

Alphanumeric 1960s

Text 1970s

Image 1990s

Speech 2000s

Music 2000s

Video 2000s

HD video 2010s

010101011100101010101010101010111010101010101010101010101010100101010101000010110101010101010010101101101010101010110010110010101010100101110101001010010101010101010001001010101011010011010010101010100101101001011100101010101001010101000101010101010101010010101001010101001001001001010101001000101010101110100101001010101010010101010101001010100100101010010101001001010101001010100101010100101010101001010101011110101011100001111011

All data is binary

Data + a code → information

Let’s encode this image

Each pixel has a color

Each color has a code

12 colors, 12 codes

Color CodeBlue 0000Light green 0001Dark green 0010Yellow 0011Orange 0100Red 0101Purple 0110Light grey 0111Dark grey 1000Brown 1001Black 1010White 1011

The image is 800 by 500 pixels

0000 0000 00001011 1011 1011 0101 0101

The codes for a few pixels

800 pixels

500

pixe

ls

How much memory or storage?

800 pixels

500

pixe

ls

• 500 x 800 = 400,000 pixels• 4x400,000 = 1,600,000 bits• 1,600,000/8 = 200,000 bytes

How much memory or storage?

Could we have had more than 12 colors?

Color CodeBlue 0000Light green 0001Dark green 0010Yellow 0011Orange 0100Red 0101Purple 0110Light grey 0111Dark grey 1000Brown 1001Black 1010White 1011

Color CodeBlue 0000Light green 0001Dark green 0010Yellow 0011Orange 0100Red 0101Purple 0110Light grey 0111Dark grey 1000Brown 1001Black 1010White 1011

1100110111101111

Four unused combinations

More bits means more unique codes

A 00B 01C 10D 11

A 0B 1

A 000B 001C 010D 011E 100F 101G 110H 111

A 0000B 0001C 0010D 0011E 0100F 0101G 0110H 0111I 1000J 1001K 1010L 1011M 1100N 1101O 1110P 1111

1-bit code 2-bit code 3-bit code 4-bit code

Do you see a pattern here?

A 000B 001C 010D 011E 100F 101G 110H 111

Start with a three bit code

What is the effect of adding a bit?

000001010011100101110111

Make two copies

What is the effect of adding a bit?

000001010011100101110111

00000001001000110100010101100111

Add a zero to one copy and 1 to the otherDoubling the number of possibilities

What is the effect of adding a bit?

10001001101010111100110111101111

A 0000B 0001C 0010D 0011E 0100F 0101G 0110H 0111

A 000B 001C 010D 011E 100F 101G 110H 111

3-bit code 4-bit code

I 1000J 1001K 1010L 1011M 1100N 1101O 1110P 1111

Adding a bit doubles the number of codes

Color depth

8 bits per pixel → 256 colors

16 bits per pixel → 65.5 thousand colors

24 bits per pixel → 16.7 million colors

32 bits per pixel → 4.3 billion colors

96% reduction – obvious information loss

Both have the same number of pixels – explain the loss of information.

1,080,000 pixels, no information

Pixels ↑ information ↑

Bits per pixel ↑ possible colors ↑ information ↑

The amount of information in an image

An image with a lot of information

http://som.csudh.edu/fac/lpress/presentations/telegeography2010cablemap.jpg

Even more information

http://www.dresden-26-gigapixels.com/dresden26GP

http://gigapan.org/

A library of information-rich images

Summary

Color CodeBlue 0000Light green 0001Dark green 0010Yellow 0011Orange 0100Red 0101Purple 0110Light grey 0111Dark grey 1000Brown 1001Black 1010White 1011

Self-study questions

An image is 800 by 500 pixels, and each pixel can be one of 12 colors. How much memory would it require?

An image is 800 by 500 pixels, and each pixel can be one of 256 colors. How much memory would it require?

How many different colors could one represent using an 8 bit code? A nine bit code?

Can you write a formula to compute the number of unique codes possible given the number of bits in a code?

Information rich images:

http://www.dresden-26-gigapixels.com/dresden26GP

http://som.csudh.edu/fac/lpress/presentations/telegeography2010cablemap.jpg

http://gigapan.org/

http://gigapixel.com

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