Histogram Equalization

Adviser ：葉家宏 老師Presenter ：邱怡雯Date : 2011/03/28

Outline

Introduction

Results Global histogram equalization Local histogram equalization

Conclusions

Introduction

Step 1: Find histogram of input imageStep 2: Calculate the CDF of each gray level valueStep 3: Mapping to new gray level table

Results Global histogram equalization

Results

1 23 45 67 89 1111331551771992212430

1000

2000

3000

4000

5000

6000

GOLDHILL-before

GOLDHILL-be-fore

1 21 41 61 81 1011211411611812012212410

2000400060008000

1000012000140001600018000

JET-before

JET-before

1 23 45 67 89 1111331551771992212430

500100015002000250030003500400045005000

PEPPER-before

PEPPER-before

1 24 47 70 93 1161391621852082312540

2000

4000

6000

8000

10000

12000

14000

TIFFANY-before

TIFFANY-before

Results

1 23 45 67 89 1111331551771992212430

1000

2000

3000

4000

5000

6000

GOLDHILL-after

GOLDHILL-after

1 20 39 58 77 96 1151341531721912102292480

2000400060008000

1000012000140001600018000

JET-after

JET-after

1 23 45 67 89 1111331551771992212430

500100015002000250030003500400045005000

PEPPER-after

PEPPER-after

1 23 45 67 89 1111331551771992212430

2000

4000

6000

8000

10000

12000

14000

TIFFANY-after

TIFFANY-after

Global histogram equalization

Results Local histogram equalization

Results

1 23 45 67 89 1111331551771992212430

200400600800

10001200140016001800

GOLDHILL-local

GOLDHILL-local

1 20 39 58 77 96 1151341531721912102292480

1000

2000

3000

4000

5000

6000

7000

JET-local

JET-local

1 23 45 67 89 1111331551771992212430

200400600800

100012001400160018002000

PEPPER-local

PEPPER-local

1 23 45 67 89 1111331551771992212430

1000

2000

3000

4000

5000

6000

7000

TIFFANY-local

TIFFANY-local

Local histogram equalization

Conclusions

Histogram equalization can increase the contrast of many images