Skills: noneConcepts: the amount of information in an image

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Compression and information

Where does this topic fit?

• Internet concepts– Applications– Technology– Implications

• Internet skills– Application development– Content creation (image)– User skills

Original

29% reduction

96% reduction

256 colors

2 colors4 colors8 colors16 colors

64 colors128 colors 32 colors

Less variety → less information

Fewer pixels → less information

322 X 345111,090 pixels355 X 383

135,965 pixels

Summary

1. We can tolerate lossy compression for images. Is lossy compression of text permissible?

2. If we used a lossy compression technique on an audio file, what would happen?

3. The image of Lucas remained the same size -- 359 by 381 pixels after we compressed it, but something changed – what changed?

4. How is lossless compression of a spreadsheet or text file possible if if none of the numbers or letters change? What must have changed? (Hint: review our presentation Data + code → information).

5. If the pixels making up an image can have only two different colors – for example black or white – how many bits do you need to store each pixel?

6. If the pixels making up an image can have only four different colors – for example black, white, and two shades of grey – how many bits do you need to store each pixel?

7. We saw that compressing an image or resizing it to be smaller discarded information. Does resizing an image to make it larger create new information?

Questions