Usability of Digital Cameras for Verifying Physically Based ...

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(a) (b) (c) Figure 57: Scatter plots of (a) L ∗ , (b) a ∗ , and (c) b ∗ values for using an ICC profile for test case 1 (8bit), comparing measured values to reproduced values. 76
Using an ICC profile obviously improves the quality of camera characterization compared to relying on the camera’s color space only. Although the mean ∆E∗ ab 10∆E∗ ab . value is only slightly lower, the maximum value could be reduced by around 7.3 Implementing an Adapted Mapping In order to be able to convert the RGB values of a photograph to XYZ space one has to find a transformation that provides a best agreement between these RGB values and the measured XYZ values. ICC profiles internally use either look-up- tables or matrices to implement this transformation. We implemented a mapping by ourselves for two reasons: first, this mapping possibly yields better results because we can better address particular properties of our data and secondly, because we also wanted to provide an approach that does not rely on expensive profiling software, but gives more accurate results than using the camera’s color space. Izadan and Nobbs [Iza06] did a comparison between iteration and regression methods using either XYZ or L ∗ a ∗ b ∗ color space. Basically, all methods yield comparable results. They conclude that regression method with L ∗ a ∗ b ∗ approach will lead to the best results. We based our calculations on polynomial regression with least squares fitting described by Hong et al. [HLR00], who have shown that a higher order polynomial is able to produce satisfactory characterization accuracy. Let R ∈ R n×m denote a matrix of RGB vectors and L ∈ R n×3 the correspond- ing matrix of L ∗ a ∗ b ∗ vectors, the mapping from RGB to L ∗ a ∗ b ∗ can be represented by L = RM, (1) where the matrix M ∈ R m×3 is derived by the following equation: M = (R T R) −1 R T L. (2) Here, n is the number of samples and m is the number of terms of the polyno- mials. The number and the grade of these terms define the type of the mapping. As our image is gamma corrected and therefore not linear, a higher order polynomial will most probably give better results than a linear polynomial. On the other 77
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DISSERTATION Usability of Digital C
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Kurzfassung Physically Based Render
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Acknowledgements I want to thank We
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3 Colorimetry 32 3.1 Color Spaces .
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E.5 Treating the Camera as a Black
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20 The CIE 1931 chromaticity diagra
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53 (a) Density plot for using the c
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List of Tables 1 Camera settings th
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1 Introduction In recent years, a l
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1.3 Applications of Physically Base
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matter are calculated in XYZ space.
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Figure 2: A photograph of the real
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(a) Photo (b) Default (c) 2 Bounces
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y a light source on top of the cube
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Figure 7: Points A to F were select
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Figure 9: A difference image of pho
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Figure 12: From top to bottom: a hi
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(a) Figure 13: (a) Left side: measu
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Figure 14: Six photocells were posi
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Figure 16: The left image shows a r
Page 41 and 42: (a) (b) Figure 18: (a) The validati
Page 43 and 44: shape of the caustic. 2.3 Analytica
Page 45 and 46: two test cases, but instead of the
Page 47 and 48: segments of the sphere and its actu
Page 49 and 50: of luminance [GJB80]. In XYZ color
Page 51 and 52: where L ∗ � � Y m = 903.3 Yn
Page 53 and 54: (a) (b) Figure 21: Chromaticity dia
Page 55 and 56: 4 Digital Cameras Pattanaik et al.
Page 57 and 58: Figure 23: The RAW image data is co
Page 59 and 60: 5 Physically Based Rendering System
Page 61 and 62: see section 7.4. By avoiding XYZ sp
Page 63 and 64: Figure 27: The sensor plane marking
Page 65 and 66: (a) (b) Figure 30: (a) ColorChecker
Page 67 and 68: available on MAC systems. We chose
Page 69 and 70: (a) (b) (c) Figure 34: Standard dev
Page 71 and 72: Figure 35: Eighty measurement spots
Page 73 and 74: (a) (b) (c) (d) Figure 37: (a) Lumi
Page 75 and 76: (a) (b) Figure 40: (a) Luminance di
Page 77 and 78: i \ j 0 1 2 3 4 5 6 7 8 9 10 11 12
Page 79 and 80: (a) (b) (c) (d) Figure 43: (a) Lumi
Page 81 and 82: (a) (b) Figure 46: Standard deviati
Page 83 and 84: (a) (b) Figure 49: (a) The measurem
Page 85 and 86: of each patch using a spectrophotom
Page 87 and 88: Figure 51: L ∗ a ∗ b ∗ differ
Page 89 and 90: (a) (b) Figure 53: (a) Density plot
Page 91: (a) (b) (c) Figure 55: Histograms o
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Page 99 and 100: in the light transport simulation o
Page 101 and 102: the internal data of a camera and w
Page 103 and 104: etter results: One can measure the
Page 105 and 106: Figure 62: A Mathematica generated
Page 107 and 108: their internal color space. This mi
Page 109 and 110: Figure 66: Surface reflectance valu
Page 111 and 112: as bad compared to other methods. S
Page 113 and 114: in sufficient detail. The approach
Page 115 and 116: A Radiometric and Photometric Quant
Page 117 and 118: B.6 Goniophotometer A goniophotomet
Page 119 and 120: C.3 Color Chart Figure 68: A Konica
Page 121 and 122: D Web Resources of Validation Data
Page 123 and 124: 8 bit jpg 16 bit 29 11.58 11.52 11.
Page 127 and 128: E.2 Using an ICC Profile 8 bit jpg
Page 131 and 132: 8 bit jpg 16 bit 124 11.08 10.89 11
Page 133 and 134: 1 2 3 4 31 9.10 3.61 4.26 5.96 32 8
Page 135 and 136: 1 2 3 4 93 6.25 4.11 4.05 8.69 94 4
Page 137 and 138: E.4 Adaptive Mapping - Higher Order
Page 139 and 140: 5 6 7 8 9 10 11 62 3.42 2.52 2.51 2
Page 141 and 142: 5 6 7 8 9 10 11 124 2.10 2.14 2.96
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R G B 31 -38.94 -25.49 29.26 32 -9.
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R G B 93 103.86 109.28 55.06 94 31.
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References [3dS06] 3D Studio Max: w
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[HLR00] Guowei Hong, M. Ronnier Luo
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Color Imaging Conference, pages 250
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[VMKK00] V. Volevich, K. Myszkowski
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