Color Effects from LUT

The image processing topic that is going to be presented this time will be very short but it's an interesting theme which is largely used to apply specific color effects to an image. I'm talking about the LUT (Lookup Tables). All you must know to follow this tutorial is how to read the content of a file whatever the programming language you are using.
Now, let's talk about what we can find in a LUT file. It can contain tones of data but in our case, what you will generally find is 256 lines filled each time with 3 values (separated by spaces).
What are these 3 values? Well... It's again the values of our 3 (Red,Green,Blue) pixel components. And why there are exactly 256 lines? These lines correspond to the different intensity levels that a pixel of an image can take. The intensity level of a pixel is a value between 0 and 255 so there are 256 possibilities of values. Let's see how to apply a LUT to an image...

The first thing you have to do is to transform your image in grey level with the method of your choice. You may understand that you can get different results with just one LUT by changing the grey level method that you apply on your image. If you don't know how to transform your image in grey level, I can only suggest you to read my last post where you will find all what you need. What we have to do after this is to replace all pixel components of our grey level image by their corresponding values in the LUT. We won't open a file and read the line corresponding to the intensity level of the current grey pixel for each pixel of our image obviously. The best thing we can do is to load all data of the LUT file in an array of 256 indexes. Each index will contain 3 values: Red, Green, Blue. At the index i (I mean at array.(i)), there will be the (Red,Green,Blue) values retrieved at the line i in the LUT file and corresponding to the color that will replace all pixels of your grey level image that have an intensity level of i. In conclusion, the function which applies a color effect from a LUT to an image may look like that :

As you see, we get the array corresponding to the LUT that we want to apply to our image with the get_lut function, then we browse the image matrix representation, we get the grey level of the current pixel with the get_grey function which returns a (Grey,Grey,Grey) pixel (according to the grey level method we want to use which explains the presence of the parameter style which is just a string variable) and we replace the current pixel by the new (Red,Green,Blue) values located at the index r of the array where r is the grey level value of the Red component of the current pixel (but I could have written array.(g) or array.(b) because the grey level of a pixel verifies Red=Green=Blue).
Now, here is the get_lut function :

Some explanations : Firstly, the integer n determines the name of the LUT file that will be open. Then we create an array of 256 indexes initialized with (0,0,0). It's this same array that will be send to the previous lut function after getting all the data of the LUT file. We have a counter named cpt which will help us to fill the 256 indexes of the array. We open the specified file and while we are not at the end of this file, we get a line in a string variable, we split each line into 3 values which represent a new (Red,Green,Blue) pixel (note that I have a function named split which can put all elements of a string variable in a list, the character used to separate these elements must be specified, plus, the ios function converts a string variable to an integer (ios stands for int_of_string)) and we fill the current index with these 3 values. Finally, at the end of the file, we can close it and send the array to the previous lut function.

Here is the content of the LUT_autumn, LUT_copper, LUT_fire, LUT_jet and LUT_spectrum files and the different results of these effects using at each time the "Averaging" grey level method.

Autumn

Copper

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

Fire

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

Jet

0 0 131
0 0 135
0 0 139
0 0 143
0 0 147
0 0 151
0 0 155
0 0 159
0 0 163
0 0 167
0 0 171
0 0 175
0 0 179
0 0 183
0 0 187
0 0 191
0 0 195
0 0 199
0 0 203
0 0 207
0 0 211
0 0 215
0 0 219
0 0 223
0 0 227
0 0 231
0 0 235
0 0 239
0 0 243
0 0 247
0 0 251
0 0 255
0 4 255
0 8 255
0 12 255
0 16 255
0 20 255
0 24 255
0 28 255
0 32 255
0 36 255
0 40 255
0 44 255
0 48 255
0 52 255
0 56 255
0 60 255
0 64 255
0 68 255
0 72 255
0 76 255
0 80 255
0 84 255
0 88 255
0 92 255
0 96 255
0 100 255
0 104 255
0 108 255
0 112 255
0 116 255
0 120 255
0 124 255
0 128 255
0 131 255
0 135 255
0 139 255
0 143 255
0 147 255
0 151 255
0 155 255
0 159 255
0 163 255
0 167 255
0 171 255
0 175 255
0 179 255
0 183 255
0 187 255
0 191 255
0 195 255
0 199 255
0 203 255
0 207 255
0 211 255
0 215 255
0 219 255
0 223 255
0 227 255
0 231 255
0 235 255
0 239 255
0 243 255
0 247 255
0 251 255
0 255 255
4 255 251
8 255 247
12 255 243
16 255 239
20 255 235
24 255 231
28 255 227
32 255 223
36 255 219
40 255 215
44 255 211
48 255 207
52 255 203
56 255 199
60 255 195
64 255 191
68 255 187
72 255 183
76 255 179
80 255 175
84 255 171
88 255 167
92 255 163
96 255 159
100 255 155
104 255 151
108 255 147
112 255 143
116 255 139
120 255 135
124 255 131
128 255 128
131 255 124
135 255 120
139 255 116
143 255 112
147 255 108
151 255 104
155 255 100
159 255 96
163 255 92
167 255 88
171 255 84
175 255 80
179 255 76
183 255 72
187 255 68
191 255 64
195 255 60
199 255 56
203 255 52
207 255 48
211 255 44
215 255 40
219 255 36
223 255 32
227 255 28
231 255 24
235 255 20
239 255 16
243 255 12
247 255 8
251 255 4
255 255 0
255 251 0
255 247 0
255 243 0
255 239 0
255 235 0
255 231 0
255 227 0
255 223 0
255 219 0
255 215 0
255 211 0
255 207 0
255 203 0
255 199 0
255 195 0
255 191 0
255 187 0
255 183 0
255 179 0
255 175 0
255 171 0
255 167 0
255 163 0
255 159 0
255 155 0
255 151 0
255 147 0
255 143 0
255 139 0
255 135 0
255 131 0
255 128 0
255 124 0
255 120 0
255 116 0
255 112 0
255 108 0
255 104 0
255 100 0
255 96 0
255 92 0
255 88 0
255 84 0
255 80 0
255 76 0
255 72 0
255 68 0
255 64 0
255 60 0
255 56 0
255 52 0
255 48 0
255 44 0
255 40 0
255 36 0
255 32 0
255 28 0
255 24 0
255 20 0
255 16 0
255 12 0
255 8 0
255 4 0
255 0 0
251 0 0
247 0 0
243 0 0
239 0 0
235 0 0
231 0 0
227 0 0
223 0 0
219 0 0
215 0 0
211 0 0
207 0 0
203 0 0
199 0 0
195 0 0
191 0 0
187 0 0
183 0 0
179 0 0
175 0 0
171 0 0
167 0 0
163 0 0
159 0 0
155 0 0
151 0 0
147 0 0
143 0 0
139 0 0
135 0 0
131 0 0
128 0 0

Spectrum

Download the files there...

How the Image Processing works?

Thursday, May 8, 2014

Color Effects from LUT