1. CS 101 – Nov. 18 Finish image enhancement Communication (Chapter 15)
Basic communication model
Cryptography
Error detection
Local Area Networks

2. Filters on Steroids Darken OK Brighten OK Darken too much
Brighten too much

3. Filters on Steroids (cont’d)
+ Contrast OK
- Contrast OK
Too much contrast
Too little contrast

4. Enhancements How to tell if image needs enhancing? Image processing
 Histogram can help.
Image processing
Detecting edges and blobs
Applications: maze; counting stars
Photoshop
inspect, make simple changes to image

5. Histogram Shows distribution of pixel values
2 operations based on histogram:
“histogram stretching”: increase contrast
“thresholding”: Use low points in distribution to serve as cut-offs to reduce the dynamic range. E.g. Dynamic range of 4 (0-3) would require 3 thresholds.

7. This one may need help

8. Communication model Claude Shannon, 1940s Broadcast = 1 to many
Networking = 1 to 1
Six elements:
Source
Destination
Transmitter
Receiver
Channel/medium
_____________
For more on Shannon’s vast contributions, please watch

9. Two directions Transmit: Receive:
Encode your message in binary (e.g. ASCII)
Encrypt if desired
Receive:
Decrypt if necessary
Decode from binary to ordinary text

10. Cryptography Big research area Terminology: Plaintext Ciphertext
Encrypt & decrypt functions

11. Encryption examples Caesar cipher Cryptogram
One-time Pad & Japanese Naval Codes
Dictionary table
Additive table
Destroy each page as you use it

12. Breaking codes Like solving a cryptogram
Distribution of letters (‘e’ versus ‘q’)
Digraphs, trigraphs
Common words
Eric Nave’s “Betrayal at Pearl Harbor”