1 of 17 Digital Image Processing Image Enhancement Ashourian

2 of 32 Contents –What is image enhancement? –بهبود کیفیت تصویر چیست –Different kinds of image enhancement –انواع روشهای بهبود کیفیت تصویر –Histogram processing –پردازش هیستوگرام –Point processing –پردازش نقطه ای –Neighbourhood operations –عملیات همسایه ای

3 of 32 A Note About Grey Levels رنج دامنه بین 0 تا 255 یا 0 تا 1 است

4 of 32 What Is Image Enhancement? The reasons for doing this include: –Highlighting interesting detail in images –Removing noise from images –Making images more visually appealing –هدف از بهبود کیفیت تصویر مشخص کردن بهتر جزییات در تصویر حذف نویز دلپذیر تر بودن از نگاه چشم است

5 of 32 Image Enhancement Examples

6 of 32 Image Enhancement Examples (cont…)

7 of 32 Image Enhancement Examples (cont…)

8 of 32 Image Enhancement Examples (cont…) Images taken from Gonzalez & Woods, Digital Image Processing (2002)

9 of 32 Spatial & Frequency Domains There are two broad categories of image enhancement techniques –Spatial domain روشهای تغییر در حوزه مکان Direct manipulation of image pixels –Frequency domain روشهای تغییر در حوزه فرکانس Manipulation of Fourier transform or wavelet transform of an image این فصل در مورد حوزه مکان می باشد

10 of 32 Image Histograms The histogram of an image shows us the distribution of grey levels in the image Massively useful in image processing, especially in segmentation هیستوگرام فراوانی روشنایی ها را نشان می دهد Grey Levels Frequencies

11 of 32 Histogram Examples Images taken from Gonzalez & Woods, Digital Image Processing (2002)

12 of 32 Histogram Examples (cont…) Images taken from Gonzalez & Woods, Digital Image Processing (2002)

13 of 32 Histogram Examples (cont…) Images taken from Gonzalez & Woods, Digital Image Processing (2002)

14 of 32 Histogram Examples (cont…)

15 of 32 Histogram Examples (cont…) Images taken from Gonzalez & Woods, Digital Image Processing (2002)

16 of 32 Histogram Examples (cont…) Images taken from Gonzalez & Woods, Digital Image Processing (2002)

17 of 32 Histogram Examples (cont…) Images taken from Gonzalez & Woods, Digital Image Processing (2002)

18 of 32 Histogram Examples (cont…) Images taken from Gonzalez & Woods, Digital Image Processing (2002)

19 of 32 Histogram Examples (cont…) Images taken from Gonzalez & Woods, Digital Image Processing (2002)

20 of 32 Histogram Examples (cont…) Images taken from Gonzalez & Woods, Digital Image Processing (2002)

21 of 32 Histogram Examples (cont…) Notice the relationships between the images and their histograms Note that the high contrast image has the most evenly spaced histogram تصاویری که کنتراست بیشتری دارند هیستوگرامشان پخش تر است

22 of 32 Contrast Stretching چگونه می توان کنتراست را تغییر داد؟

23 of 32 Histogram Equalisation فرمول جبرانسازی هیستوگرام The formula for histogram equalisation is given where –r k :input intensity –s k :processed intensity –k : the intensity range (e.g 0.0 – 1.0) –n j :the frequency of intensity j –n :the sum of all frequencies

24 of 32 Equalisation Transformation Function Images taken from Gonzalez & Woods, Digital Image Processing (2002)

25 of 32 Equalisation Examples Images taken from Gonzalez & Woods, Digital Image Processing (2002) 1

26 of 32 Equalisation Transformation Functions The functions used to equalise the images in the previous example

27 of 32 Equalisation Examples 2

28 of 32 Equalisation Transformation Functions The functions used to equalise the images in the previous example

29 of 32 Equalisation Examples (cont…) 3 4

30 of 32 Equalisation Examples (cont…) 3 4

31 of 32 Equalisation Transformation Functions The functions used to equalise the images in the previous examples

32 of 32 Summary We have looked at: –Different kinds of image enhancement –Histograms –Histogram equalisation Next time we will start to look at point processing and some neighbourhood operations