Richard Sharman.

Transcription

1 Richard Sharman GP 2007

2 Making the most of your bits Common picture problems Auto-fix Algorithms Exposure correction Solutions Summary 2

3 Common picture problems Under exposure Backlit Snow/beach Over Exposure Clipping Close flash 3

4 Autofix Processes Cameras Auto-white Auto-exposure Photo processing Auto-levels Auto-contrast 4

5 Levels Camera original Green channel Corrected picture Corrected green 5

6 Auto-contrast Camera original After auto-contrast 6

7 Auto-levels Camera original After auto-levels 7

8 Exposure correction Unbuild/adjust gain/rebuild Standards Adjust gain/correct gamma 8

9 Exposure correction Unbuild/adjust/rebui ld Display space Scene space Un-build Adjust gain Display space Re-build 9

10 OECF standard ISO Photography Electronic still-picture cameras Methods for measuring opto-electronic conversion function (OECFs) Camera under test Light Test chart Light 10

11 srgb Standard IEC Colour Measurement and Management in Multimedia Systems and Equipment Part 2-1 Default colour space - srgb Gamma output = Scene Input * for (Scene Input <= ) = 1.055*Scene Input^(1/2.4)) for (Scene Input > ) Scene = Gamma Input/12,93 for (Gamma Input <= ) =((Gamma Input+0.055)/1.055)^2.4)) for (Gamma Input > ) 11

12 Unbuild/rebuild normal Camera original After unbuild After unbuild/rebuild 12

13 Missing values What does it mean How many bits How regenerate them 13

14 How many bits 8 bits 8 bits 7 bits 7 bits 6 bits 6 bits 8 bits 8 bits 7 bits 7 bits 6 bits 6 bits 14

15 Unbuild/rebuild normal Camera original After unbuild After unbuild/rebuild After JPEG save 15

16 -2 stops unbuild/rebuild - 2 Stops original Unbuilt Gain corrected Gamma corrected 16

17 -2 stops unbuild/rebuild, after JPEG save Normal -2 Stops TIFF -2 Stops JPEG 10-2 Stops JPEG 7 17

18 Exposure correction Gain/gamma correct Adjust gain Adjust gamma 18

19 -1 Stop original -1 Stop level corrected -1 Stop gamma corrected 19

20 Normal -1 Stop unbuild/build -1Stop gain/gamma 20

21 -1 Processed to match normal -1 Processed using soft clip 21

22 -2 Stops original -2 Stops level corrected -2 Stops gamma corrected 22

23 Normal -2 Stops unbuild/rebuild -2 Stops gain/gamma JPEG 10 save 23

24 +1 stop unbuild/rebuild +1 Stop original Unbuild Gain correct Gamma correct 24

25 +1 stop gain/gamma correction +1 Stop original Gain corrected Gamma corrected 25

26 Normal +1 Stop unbuild/build +1Stop gain/gamma 26

27 Gain/gamma Normal +1 Stop -1 Stop -2 Stop Auto-levels 27

28 Auto-levels Camera original Corrected Auto-contrast 28

29 Auto-levels Camera original Corrected Auto-contrast 29

30 Camera original TIFF Histogram JPEG Histogram 30

31 Bits Summary Take an exposure series of a picture with some reference colours Use soft clips instead of hard clips Generate a range of correction curves JPEG save 31

32 Making the most of your pixels Applications Interpolation methods Picture sizes Preparing the picture Conclusions 32

33 Applications Whole picture enlargements Selective enlargements 33

34 Interpolation methods Pixel replicate Bilinear Bicubic Stair step Photo-Zoom S-Spline Fractal 34

35 PhotoZoom screen shot 1 35

36 PhotoZoom screen shot 2 36

37 Genuine Fractal screen shot 1 37

38 Genuine Fractal screen shot 2 38

39 Zoom examples x2/4 Bicubic S-spline XL Fractal x2 x4 39

40 Zoom examples x6/8 Bicubic S-spline XL Fractal x6 x8 40

41 Selective enlargements 175% Camera originals Bi-cubic S-spline XL Fractals 41

42 Selective enlargements 400% Camera originals Bi-cubic S-spline XL Fractals 42

43 Selective enlargements 600% Camera originals Bi-cubic S-spline XL Fractals 43

44 Picture Size Pixels vs. picture size, cm Sensor size Total Pixels 3M pixel 2048 x Mpixel 2848 x M pixel 3264 x Mpixel 3648 x 2736 True Pixels (single chip) 75% Quality print size 250ppi X2Poster 150ppi X4 Poster 150ppi 1536x x x 12 Acceptable print /x1 poster 150ppi 35 x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x

45 Picture Size Pixels vs. picture size, inches Sensor size Total Pixels 3M pixel 2048 x Mpixel 2848 x M pixel 3264 x Mpixel 3648 x 2736 True Pixels (single chip) 75% Quality print size 250ppi X2Poster 150ppi X4 Poster 150ppi 1536x x6 6 x 4.5 Acceptable print size/x1poster 150ppi 14 x x 8 27 x x 15 54x x x x x x x x x x x x x x 7 22 x x x x x x x x x 8 24 x x x x x x 56 45

46 Picture preparation Use the highest quality setting from your camera with maximum number of pixels Use sharpest image setting you can, from camera, which gives no obvious edge effect Use the lowest ISO setting to give the lowest noise level in the picture Use tripod and/or flash 46

47 Pixel conclusions For whole picture enlargements up to x4 using bicubic, s-spline, or fractals or x8+ using sspline For selective enlargements up to x4 47