D.3 Reflective Display Systems

This last example illustrates how conformance with the Grayscale Standard Display Function may be achieved for a thermal-dye-transfer paper printer/office-light system. The thermal-dye-transfer printer produces black-and-white grayscale prints on a semi-glossy 8-inch x 10-inch heavy-gauge paper. The print is illuminated uniformly by fluorescent lamps so that the minimum reflective density produces a Luminance of 150 cd/m2. The hypothetical transformation operator is assumed to have equal input and output digitization resolution of 8 bits.

D.3.1. Measuring the system Characteristic Curve

A print with a 64-step grayscale tablet was printed for DDLs 4, 8, 12, ...,248, 252, 255. The reflection optical densities (from 0.08 to 2.80) were measured with a densitometer. The Luminance levels corresponding to the measured optical densities and illumination conditions are plotted in Fig. D.3-1.

[pic]

Figure D.3-1 Measured and interpolated Characteristic Curve and Grayscale Standard Display Function for a printer producing reflective hard-copies

D.3.2. Application of the Grayscale Standard Display Function

This last example illustrates how conformance with the Grayscale Standard Display Function may be achieved for a thermal-dye-transfer paper printer/office-light system. The thermal-dye-transfer printer produces black-and-white grayscale prints on a semi-glossy 8-inch x 10-inch heavy-gauge paper. The print is illuminated uniformly by fluorescent lamps so that the minimum reflective density produces a Luminance of 150 cd/m2. The hypothetical transformation operator is assumed to have equal input and output digitization resolution of 8 bits.

D.3.3 Implementation of the Grayscale Standard Display Function

The measured Characteristic Curve is interpolated for the available DDLs yielding 256 Luminance levels L I,m . The Grayscale Standard Display Function is also interpolated between JNDmin and JNDmax ( DJND = [ JND max - JND min ]/255) yielding 256 Standard Luminance levels L I,STD .

For every L I,STD , the closest L J,m is determined. The data pair I , J defines the transformation between D input and D output (Table D.3-1 and Fig. D.3-2) by which the Luminance response of the Display System is made to approximates the Grayscale Standard Display Function.

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Figure D.3-2 Transformation for modifying the Characteristic Curve of the printer to a Display Function that approximates the Grayscale Standard Display Function

Table D.3-1 Look-Up Table for Calibrating Reflection Hardcopy System

P-Value DDL P-Value DDL P-Value DDL P-Value DDL
0 6 1 9 2 12 3 15
4 18 5 20 6 27 7 29
8 30 9 31 10 31 11 32
12 33 13 33 14 34 15 36
16 38 17 40 18 41 19 42
20 43 21 44 22 45 23 59
24 60 25 61 26 62 27 62
28 63 29 63 30 64 31 64
32 65 33 65 34 65 35 66
36 66 37 67 38 67 39 68
40 70 41 74 42 75 43 76
44 78 45 84 46 85 47 86
48 87 49 87 50 88 51 89
52 89 53 91 54 92 55 94
56 95 57 96 58 97 59 97
60 98 61 99 62 99 63 100
64 101 65 102 66 103 67 104
68 105 69 106 70 107 71 108
72 109 73 110 74 112 75 114
76 116 77 118 78 119 79 120
80 121 81 122 82 122 83 123
84 123 85 124 86 125 87 125
88 126 89 126 90 127 91 127
92 128 93 129 94 130 95 131
96 133 97 134 98 135 99 136
100 136 101 137 102 138 103 138
104 139 105 139 106 140 107 141
108 143 109 145 110 147 111 148
112 149 113 150 114 151 115 152
116 153 117 154 118 154 119 155
120 156 121 156 122 157 123 158
124 159 125 160 126 160 127 162
128 163 129 164 130 165 131 166
132 167 133 168 134 169 135 170
136 170 137 171 138 172 139 172
140 173 141 174 142 175 143 175
144 176 145 177 146 178 147 179
148 179 149 180 150 181 151 182
152 182 153 183 154 184 155 184
156 185 157 186 158 186 159 187
160 187 161 188 162 188 163 189
164 189 165 190 166 190 167 190
168 191 169 191 170 192 171 192
172 192 173 193 174 194 175 194
176 195 177 195 178 196 179 197
180 198 181 199 182 199 183 200
184 200 185 201 186 202 187 202
188 203 189 203 190 204 191 204
192 205 193 205 194 206 195 207
196 207 197 208 198 209 199 210
200 211 201 212 202 213 203 214
204 214 205 215 206 216 207 216
208 217 209 218 210 219 211 219
212 220 213 220 214 221 215 222
216 222 217 223 218 223 219 224
220 224 221 225 222 226 223 226
224 227 225 228 226 228 227 230
228 231 229 232 230 234 231 235
232 236 233 238 234 238 235 239
236 240 237 241 238 242 239 242
240 243 241 244 242 245 243 246
244 247 245 248 246 249 247 250
248 250 249 251 250 251 251 252
252 252 253 253 254 253 255 254

D.3.4 Measures of Conformance

The FIT and LUM metrics as proposed in Annex C are applied to determine the macroscopic and microscopic approximation of the LJ,m to the LI,STD . Fig. D.3-3 shows the perceptually linearized Display Function superimposed on the Grayscale Standard Display Function and Figure D.3-4 summarizes the results of the two metrics. FIT provides as best fit of the JNDs/Luminance interval a straight line almost perfectly parallel to the horizontal axis indicating good global fit of the transformed Display Function with the Grayscale Standard Display Function. The RMSE computed by LUM is relatively large indicating more pronounced local deviations from the Grayscale Standard Display Function as, for example, with the soft-copy Display System illustrated in Section D.1. At least in part, the larger RMSE is due to the fact that the input and output digitization resolution for the transform are equal. The transformation table (Table D.3-1) and Fig. D.3-2 show that several P-Values lead to the same Luminance levels on the transformed Display Function. In fact, only 205 of the 255 Luminance intervals lead to JNDs for the Standard Target.

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Figure D.3-3. Transformed Display Function and superimposed Grayscale Standard Display Function for a reflective hard-copy Display System. The transformed Display Function for this Display System matches the Grayscale Standard Display Function and the two curves are superimposed and indistinguishable.

[pic]

Figure D.3-4 Measures of conformance for a reflective hard-copy Display System with equal input and output digitization resolution of 8 bits