1. Camera Film-Filter Systems Lecture 4 Prepared by R. Lathrop 9/99 Updated 9/06

2. Radiometric Characteristics of aerial photos Film exposure at a point in a photograph is directly related to the reflectance of the object imaged at that point. Theoretically, film exposure varies linearly with object reflectance, with both being a function of wavelength. From Lillesand & Kiefer, 1994

3. Film Exposure Exposure, E = s * d 2 * t / 4 f 2 where E = film exposure, J mm -2 s = scene brightness, J mm -2 sec -1 d = diameter of lens opening, mm t = exposure time, sec f = focal length of lens, mm

4. Black & White Film B&W Panchromatic: sensitive to ultraviolet - blue -green - red (0.3 to 0.7  m) B&W Infrared: sensitive to UV to NIR (0.3 to 0.90  m) Ultraviolet blocked by haze filter

5. B&W Film Exposure process Silver halide grains in the film emulsion absorb light energy and are reduced to silver atoms During processing, the grains not exposed to light are dissolved and washed away Emulsion Base light Silver halide grains Developed film negative with metallic silver

6. B&W Film Exposure process After processing, film areas that were exposed become various shades of gray, depending on the amount of exposure Full exposure = black No exposure = white In the negative, bright areas appear dark as there is a higher concentration of silver Processing

7. Negative-to-Positive Photo Sequence To create a positive, the negative is illuminated and photographic print paper is exposed In the positive, dark areas on the negative now appear bright and bright areas appear dark, thereby back to the original object tones Processing w/ enlarging

8. Film transmittance Transmittance, T, ability of a film to pass light T p = light passing through film at point p total light incident upon the film at pt. p Opacity, O, is a measure of “darkness” of a film emulsion O p = 1/T p 40 units transmitted T p = 40/100 = 0.40 10 units transmitted T p = 10/100 = 0.10 1 unit transmitted T p = 1/100 = 0.01 Adapted from Lillesand & Kiefer

9. Film Density Density, D p = log (O p ) = log (1/T p ) Image density and visual tone vary in a nearly linear relationship

10. D - Log Exposure curve Plot of relative log exposure on X axis vs. density on Y axis Slope of straight-line portion of curve  D =   logE Slope of straight-line portion of curve important determinant of film contrast; steeper the slope, greater the contrast, greater radiometric resolution

11. D-Log E curve Plot of relative log exposure on X axis vs. density on Y axis 0 1 2 3 D min D max  D =   logE  logE DD Straight line portion Density Relative log exposure Adapted from Lillesand & Kiefer

12. Comparing D-Log E curves 0 1 2 3 D min D max Density Relative log exposure Adapted from Lillesand & Kiefer Film 1 Film 2 Density resolution Radiometric resolution

13. D - Log Exposure curve Slope of straight-line portion of curve, , important determinant of film contrast Steeper the slope, greater radiometric resolution (i.e. smallest detectable change in exposure), leads to imagery with greater contrast Film 1 has steeper  and higher radiometric resolution, greater contrast

14. Comparing D-Log E curves 0 1 2 3 D min D max Density Relative log exposure Adapted from Lillesand & Kiefer Film 1 Film 2 Density resolution Radiometric resolution

15. D - Log Exposure curve Film speed is the sensitivity of a film to light Fast film accommodates low exposure levels (i.e. it lies farther to the left on the log E axis) Film 1 is a faster film but has more limited exposure range as compared to Film 2 Tradeoff between film speed and coarser spatial resolution (larger film grains to capture low light) Film 2 provides a finer grain film

16. Comparing D-Log E curves 0 1 2 3 D min D max Density Relative log exposure Adapted from Lillesand & Kiefer Film 1 Film 2 Density resolution Radiometric resolution

17. Exposure Falloff Falloff: less light, lower exposure towards edge of image frame

18. White Light is a combination of all the visible wavelengths

19. 400 500 600 700 wavelength (nm) Human Color Vision 3 types of cones: roughly sensitive with peaks in the blue (445nm), green (535nm) and orange-red (575nm)

20. Primary Colors Red Green Blue

21. Color Additive Process R G B M Y C W Black background

22. Subtractive Primary Colors Yellow (R+G) absence of blue Cyan (G+B) absence of red Magenta (R+B) absence of green

23. YC M R G B B Color Subtractive Process White background

24. Color film 3 dye layers sandwiched to a base Yellow dye layer controls blue light passing through image Magenta dye layer controls green light Cyan dye layer controls red light Blue sensitive layer Blue blocking filter G (& B) sensitive layer R (& B) sensitive layer Base & Backing

25. Color film Film Image colors GR Original colors YMC BGR Dye Layers B

26. Color Infrared (CIR) film Blue absorbing filter Near infrared sensitive dye layer - cyan dye which controls red light on image Green sensitive layer - yellow dye which controls blue light on image Red sensitive dye layer - magenta dye which controls green light on image Blue blocking filter NIR (& B) sensitive layer G (& B) sensitive layer R (& B) sensitive layer Base & Backing

27. Color Infrared film Original colors Film Image colors NIR Filter GR YMC BGR Dye Layers B

28. An example-plant leaves Chlorophyll absorbs large % of red and blue for photosynthesis- and strongly reflects in green (.55um) mm Peak reflectance in leaves in near infrared (.7-1.2mm) up to 60% of infrared energy per leaf is scattered up or down due to cell wall size, shape, leaf condition (age, stress, disease), etc. Reflectance in Mid IR (2-4mm) influenced by water content-water absorbs IR energy, so live leaves reduce mid IR return

29. Color Infrared film Original colors Red to magenta NIR Filter GR YMC BGR B

30. What color is it? What color would a green astroturf field (with low NIR reflectance) look like on Color IR film? What color would a field of flowering yellow mustard plant look like on Color IR film? What color would a magenta (purple) cow (with low NIR reflectance) look like on color IR film?

31. What color would a green astroturf field (with low NIR reflectance) look like on Color IR film? Original colors Film Image colors NIR Filter GR YMC BGR B Blue

32. RU Stadium and Practice Field Natural grass Synthetic turf Photo from 1995

33. ‘False color’ imagery On a computer screen, can re-arrange the individual color layers or bands of a digital image can be switched around For a CIR, normal rendition NIR  R, R  G, G  B The image to the right is scrambled. Match the original wavebands to the display colors. ?  R, ?  G,  ?  B

34. What color would a field of flowering yellow mustard plant look like on Color IR film? Original colors Film Image colors NIR Filter GR YMC BGR Dye Layers B White to pink

35. What color would a magenta cow look like on Color IR film? Original colors Film Image colors NIR Filter GR YMC BGR Dye Layers B Green

36. Filters Short wavelength blocking filter (high pass) selectively absorbs energy below a certain wavelength Haze filters to absorb UV (<0.4 um) Yellow filter to absorb blue (<0.5 um) Bandpass filters block energy above and below a certain range of wavelengths

37. Computer Image Display Computer Display Monitor has 3 color planes: R, G, B that can display DN’s or BV’s with values between 0-255 3 layers of data can be viewed simultaneously: 1 layer in Red plane 1 layer in Green plane 1 layer in Blue plane

38. Image Display: RGB color compositing Red band DN Blue band DN Red band DN = 0 Blue band DN = 200 Green band DN Green band DN = 90 Blue-green pixel (0, 90, 200 RGB)

39. Landsat MSS bands 4 and 5 GREEN RED

40. Landsat MSS bands 6 and 7 INFRARED 2INFRARED 1 Note: water absorbs IR energy-no return=black

41. combining bands creates a false color composite Rutgers Manhattan Philadelphia Pine barrens Chesapeake Bay Delaware River MSS “false”color composite

42. RGB Additive Color Process colorRGB white255255255 black000 red25500 yellow2552550 cyan0255255 magenta2550255 orange = ___ ___ ___

43. Additive color process Snow reflects highly in the visible and near- IR wavelengths but absorbs (low DN) in the mid-IR and thermal-IR wavelengths. For a 'false color' composite that consists of NIR=red, MIR=green, and RED=blue, snow is what color? __________________

44. Additive color process Stressed vegetation with chlorophyll degradation reflects more highly in the red wavelengths than healthy green vegetation. For a ‘true color' composite that consists of Red=red, Green=green, and Blue=blue, stressed vegetation is what color? __________________ For a 'false color' composite that consists of NIR=red, Red=green, and Green=blue, stressed vegetation is what color? __________________

45. RGB Color Systems

46. IHS Color System IHS: Intensity-Hue-Saturation