1. Remote Sensing and Image Processing: 2 Dr. Hassan J. Eghbali

2. Image processing: image display and enhancement Purpose visual enhancement to aid interpretation enhancement for improvement of information extraction techniques Today we will look at image display and histogram manipulation (contrast ehancement etc.) Dr. Hassan J. Eghbali

3. Image Display The quality of image display depends on the quality of the display device used –and the way it is set up / used … computer screen - RGB colour guns –e.g. 24 bit screen (16777216) 8 bits/colour (2 8 ) or address differently Dr. Hassan J. Eghbali

4. Colour Composites ‘Real Colour’ composite red band on red green band on green blue band on blue Swanley, Landsat TM 1988 Dr. Hassan J. Eghbali

5. Colour Composites ‘Real Colour’ composite red band on red Dr. Hassan J. Eghbali

6. Colour Composites ‘Real Colour’ composite red band on red green band on green Dr. Hassan J. Eghbali

7. Colour Composites ‘Real Colour’ composite red band on red green band on green blue band on blue approximation to ‘real colour’... Dr. Hassan J. Eghbali

8. Colour Composites ‘False Colour’ composite NIR band on red red band on green green band on blue Dr. Hassan J. Eghbali

9. Colour Composites ‘False Colour’ composite NIR band on red red band on green green band on blue Dr. Hassan J. Eghbali

10. Colour Composites ‘False Colour’ composite many channel data, much not comparable to RGB (visible) –e.g. Multi-temporal data –AVHRR MVC 1995 April August September April; August; September Dr. Hassan J. Eghbali

11. Greyscale Display Put same information on R,G,B: August 1995 Dr. Hassan J. Eghbali

12. Density Slicing Dr. Hassan J. Eghbali

13. Density Slicing Dr. Hassan J. Eghbali

14. Density Slicing Don’t always want to use full dynamic range of display Density slicing: a crude form of classification Dr. Hassan J. Eghbali

15. Density Slicing Or use single cutoff = Thresholding Dr. Hassan J. Eghbali

16. Density Slicing Or use single cutoff with grey level after that point ‘Semi-Thresholding’ Dr. Hassan J. Eghbali

17. Pseudocolour use colour to enhance features in a single band –each DN assigned a different 'colour' in the image display Dr. Hassan J. Eghbali

18. Pseudocolour Or combine with density slicing / thresholding Dr. Hassan J. Eghbali

19. Histogram Manipluation WHAT IS A HISTOGRAM? Dr. Hassan J. Eghbali

20. Histogram Manipluation WHAT IS A HISTOGRAM? Dr. Hassan J. Eghbali

21. Histogram Manipluation WHAT IS A HISTOGRAM? Frequency of occurrence (of specific DN) Dr. Hassan J. Eghbali

22. Histogram Manipluation Analysis of histogram –information on the dynamic range and distribution of DN attempts at visual enhancement also useful for analysis, e.g. when a multimodal distibution is observed Dr. Hassan J. Eghbali

23. Histogram Manipluation Analysis of histogram –information on the dynamic range and distribution of DN attempts at visual enhancement also useful for analysis, e.g. when a multimodal distibution is observed Dr. Hassan J. Eghbali

24. Histogram Manipluation Typical histogram manipulation algorithms: Linear Transformation input output 0 255 0

25. Histogram Manipluation Typical histogram manipulation algorithms: Linear Transformation input output 0 255 0 Dr. Hassan J. Eghbali

26. Histogram Manipluation Typical histogram manipulation algorithms: Linear Transformation Can automatically scale between upper and lower limits or apply manual limits or apply piecewise operator But automatic not always useful... Dr. Hassan J. Eghbali

27. Histogram Manipluation Typical histogram manipulation algorithms: Histogram Equalisation Attempt is made to ‘equalise’ the frequency distribution across the full DN range Dr. Hassan J. Eghbali

28. Histogram Manipluation Typical histogram manipulation algorithms: Histogram Equalisation Attempt to split the histogram into ‘equal areas’ Dr. Hassan J. Eghbali

29. Histogram Manipluation Typical histogram manipulation algorithms: Histogram Equalisation Resultant histogram uses DN range in proportion to frequency of occurrence Dr. Hassan J. Eghbali

30. Histogram Manipluation Typical histogram manipulation algorithms: Histogram Equalisation Useful ‘automatic’ operation, attempting to produce ‘flat’ histogram Doesn’t suffer from ‘tail’ problems of linear transformation Like all these transforms, not always successful Histogram Normalisation is similar idea Attempts to produce ‘normal’ distribution in output histogram both useful when a distribution is very skewed or multimodal skewed Dr. Hassan J. Eghbali

31. Colour Spaces Define ‘colour space’ in terms of RGB Only for visible part of spectrum: Dr. Hassan J. Eghbali

32. Colour Spaces RGB axes: Dr. Hassan J. Eghbali

33. Colour Spaces RGB (primaries) as axes Dr. Hassan J. Eghbali

34. Colour Spaces Alternative: CMYK ‘subtractive primaries’ often used for printing (& some TV) Dr. Hassan J. Eghbali

35. Colour Spaces Alternative: CMYK ‘subtractive primaries’ Dr. Hassan J. Eghbali

36. Colour Spaces Other important concept: HSI transforms Hue(which shade of color) Saturation (how much color) Intensity also, HSV (value), HSL (lightness) Dr. Hassan J. Eghbali

37. Colour Spaces Other important concept: HSI transforms Dr. Hassan J. Eghbali

38. Practical 1 Histogram manipulation –Contrast stretching and histogram equalisation visual (qualitative) enhancement of images according to brightness Highlight clouds / sea / land in AVHRR image of UK Multispectral information –Different DN (digital number) values in different bands –Due to different properties of surfaces Dr. Hassan J. Eghbali