Richard Sharman richardsha@tiscali.co.uk GP 2007
Making the most of your bits Common picture problems Auto-fix Algorithms Exposure correction Solutions Summary 2
Common picture problems Under exposure Backlit Snow/beach Over Exposure Clipping Close flash 3
Autofix Processes Cameras Auto-white Auto-exposure Photo processing Auto-levels Auto-contrast 4
Levels Camera original Green channel Corrected picture Corrected green 5
Auto-contrast Camera original After auto-contrast 6
Auto-levels Camera original After auto-levels 7
Exposure correction Unbuild/adjust gain/rebuild Standards Adjust gain/correct gamma 8
Exposure correction Unbuild/adjust/rebui ld Display space Scene space Un-build Adjust gain Display space Re-build 9
OECF standard ISO 14524 Photography Electronic still-picture cameras Methods for measuring opto-electronic conversion function (OECFs) Camera under test Light Test chart Light 10
srgb Standard IEC 61966-2-1 Colour Measurement and Management in Multimedia Systems and Equipment Part 2-1 Default colour space - srgb Gamma output = Scene Input * 12.92 for (Scene Input <=0.0031308 ) = 1.055*Scene Input^(1/2.4))-0.055 for (Scene Input >0.0031308) Scene = Gamma Input/12,93 for (Gamma Input <=0.04045) =((Gamma Input+0.055)/1.055)^2.4)) for (Gamma Input >0.04045) 11
Unbuild/rebuild normal Camera original After unbuild After unbuild/rebuild 12
Missing values What does it mean How many bits How regenerate them 13
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
Unbuild/rebuild normal Camera original After unbuild After unbuild/rebuild After JPEG save 15
-2 stops unbuild/rebuild - 2 Stops original Unbuilt Gain corrected Gamma corrected 16
-2 stops unbuild/rebuild, after JPEG save Normal -2 Stops TIFF -2 Stops JPEG 10-2 Stops JPEG 7 17
Exposure correction Gain/gamma correct Adjust gain Adjust gamma 18
-1 Stop original -1 Stop level corrected -1 Stop gamma corrected 19
Normal -1 Stop unbuild/build -1Stop gain/gamma 20
-1 Processed to match normal -1 Processed using soft clip 21
-2 Stops original -2 Stops level corrected -2 Stops gamma corrected 22
Normal -2 Stops unbuild/rebuild -2 Stops gain/gamma JPEG 10 save 23
+1 stop unbuild/rebuild +1 Stop original Unbuild Gain correct Gamma correct 24
+1 stop gain/gamma correction +1 Stop original Gain corrected Gamma corrected 25
Normal +1 Stop unbuild/build +1Stop gain/gamma 26
Gain/gamma Normal +1 Stop -1 Stop -2 Stop Auto-levels 27
Auto-levels Camera original Corrected Auto-contrast 28
Auto-levels Camera original Corrected Auto-contrast 29
Camera original TIFF Histogram JPEG Histogram 30
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
Making the most of your pixels Applications Interpolation methods Picture sizes Preparing the picture Conclusions 32
Applications Whole picture enlargements Selective enlargements 33
Interpolation methods Pixel replicate Bilinear Bicubic Stair step Photo-Zoom S-Spline Fractal 34
PhotoZoom screen shot 1 35
PhotoZoom screen shot 2 36
Genuine Fractal screen shot 1 37
Genuine Fractal screen shot 2 38
Zoom examples x2/4 Bicubic S-spline XL Fractal x2 x4 39
Zoom examples x6/8 Bicubic S-spline XL Fractal x6 x8 40
Selective enlargements 175% Camera originals Bi-cubic S-spline XL Fractals 41
Selective enlargements 400% Camera originals Bi-cubic S-spline XL Fractals 42
Selective enlargements 600% Camera originals Bi-cubic S-spline XL Fractals 43
Picture Size Pixels vs. picture size, cm Sensor size Total Pixels 3M pixel 2048 x 1536 6Mpixel 2848 x 2136 8M pixel 3264 x 2448 10Mpixel 3648 x 2736 True Pixels (single chip) 75% Quality print size 250ppi X2Poster 150ppi X4 Poster 150ppi 1536x 1152 21 x 15 15 x 12 Acceptable print /x1 poster 150ppi 35 x 26 26 x 20 70 x 52 52 x 40 140 x 104 104 x 80 2136 x 1602 29 x 22 22 x 16 48 x 36 36 x 27 96 x 72 72 x 54 192 x 144 144 x 108 2448 x 1836 33 x 25 25 x 19 55 x 41 41 x 31 110 x 82 82 x 62 220 x 162 164 x 124 2736 x 2052 37 x 28 28 x 21 62 x 46 46 x 35 124 x 92 92 x 70 248 x 184 184 x 140 44
Picture Size Pixels vs. picture size, inches Sensor size Total Pixels 3M pixel 2048 x 1536 6Mpixel 2848 x 2136 8M pixel 3264 x 2448 10Mpixel 3648 x 2736 True Pixels (single chip) 75% Quality print size 250ppi X2Poster 150ppi X4 Poster 150ppi 1536x 1152 8x6 6 x 4.5 Acceptable print size/x1poster 150ppi 14 x 10 10 x 8 27 x 20 20 x 15 54x 40 40 x 30 2136 x 1602 1 1 x 8.5 8.5 x 6.5 19 x 14. 14 x 11 38 x 28 28 x 22 76 x 56 56 x 44 2448 x 1836 13 x 10 10 x 7 22 x 16 16 x 12 44 x 32 32 x 24 88 x 64 65 x 48 2736 x 2052 15 x 11 11 x 8 24 x 18 18 x 14 48 x 36 36 x 28 96 x 72 72 x 56 45
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
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