How to Stress Test LUTs in DaVinci Resolve — Transcript

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1. 0:00hi i'm stefano engeschwantner and in
2. 0:02this video i will talk about my favorite
3. 0:05test image to stress test luts i'm going
4. 0:08to talk how it's designed and i will
5. 0:10also talk about
6. 0:12this lego set here which can help us to
7. 0:14understand certain things we first
8. 0:16perceive in our
9. 0:17test image
10. 0:19and i want to close a gap between the
11. 0:21test images and real world footage
12. 0:24at the very end i will also explain the
13. 0:26limits of test images but first let's
14. 0:29get started with the color wheel
15. 0:33so here we have our well-known color
16. 0:34wheel in which primary colors red green
17. 0:37and blue are arranged in a circle
18. 0:39similar colors are next to each other
19. 0:41and the complementary colors the magenta
20. 0:44and yellow are opposite to our primary
21. 0:46colors
22. 0:47we can unroll this color wheel and scale
23. 0:49it so it will fill the entire screen
24. 0:53next we overlay grayscale gradient over
25. 0:55the image so that there is a zero to one
26. 0:57hundred percent saturation range from
27. 1:00the top to the center and a one hundred
28. 1:02to zero percent brightness range from
29. 1:05the center to the bottom of our image
30. 1:08this defines lightness as a range of
31. 1:10values of each color in a u range from
32. 1:13full saturation to zero rather than
33. 1:16actual luminance
34. 1:18first let's take a look at the kodak
35. 1:202383 lut by davinci resolve
36. 1:24i applied a node underneath where i
37. 1:26crank up the contrast and move the pivot
38. 1:28around
39. 1:30i can also activate the color space
40. 1:31transform and change the color space to
41. 1:34re-log c for example
42. 1:37we can observe that we always have a
43. 1:39smooth transition between the use and a
44. 1:41nice transition from the top to the
45. 1:43bottom of our image
46. 1:46now let's take a look at the first bad
47. 1:48lot
48. 1:50this is what it looks when i activate
49. 1:52the lot
50. 1:53if i increase the contrast we see that
51. 1:55we no longer have a smooth transition
52. 1:57between our use
53. 1:59this slot was designed for our log c so
54. 2:02it is fair to apply color space
55. 2:04transform
56. 2:05but we are still seeing the same issues
57. 2:08for comparison this is what it looks
58. 2:11like when we adjust the contrast after
59. 2:12appliance a lot
60. 2:14so it looks different
61. 2:16and if we increase the contrast and
62. 2:19pivot in this node we see that we no
63. 2:21longer have a smooth transition from top
64. 2:23to bottom
65. 2:24but from my understanding this was
66. 2:27designed to be at the very end of the
67. 2:30note 3 so i think it is fair to change
68. 2:32the contrast in the note before the lot
69. 2:34and i know some people say well i don't
70. 2:37create test images i grade real footage
71. 2:41so let's take a look at what the slot
72. 2:43does with real life images
73. 2:46so let's have a look at this test image
74. 2:48here
75. 2:49and this was shot on blackmagic pocket
76. 2:52camera 4k
77. 2:54and in the first node i applied
78. 2:56my color space transform from black
79. 2:58magic to re-log c
80. 3:00and in the second node i adjust the
81. 3:02contrast and if i change the pivot we
82. 3:05see a nice transition
83. 3:08and now i will apply the lut
84. 3:13and we can see
85. 3:14here some issues
86. 3:17and the transitions between the use
87. 3:20so here we see
88. 3:22we have a dark blue then it goes to a
89. 3:25brighter blue and
90. 3:28a dark cyan color and a bright sign
91. 3:32and this is exactly
92. 3:35what we see here in our test image too
93. 3:39so i think this test image is really
94. 3:42helpful
95. 3:43and
96. 3:45sometimes when you apply
97. 3:47a lot to
98. 3:48real footage
99. 3:49you may think well it looks good
100. 3:52in this area until
101. 3:54you have a blue jacket and then you
102. 3:56enable it
103. 3:58and then you see oh okay it's
104. 4:01um it will break my image
105. 4:04so let's move on to the next slot um bad
106. 4:07lut number two
107. 4:09so here we have our new lut i enable the
108. 4:12node with a lot in it and we can spot
109. 4:15some
110. 4:17artifacts
111. 4:18we don't have some problems here in the
112. 4:20highlights
113. 4:21and i switched to sony s lock
114. 4:25and so
115. 4:27and because
116. 4:27lut expects sony s lock as input
117. 4:30then it looks a little bit better
118. 4:34but still um
119. 4:36it doesn't make sense
120. 4:38that we have here in magenta spot and
121. 4:41the highlights
122. 4:43and if we crank up the contrast
123. 4:48and change the pivot
124. 4:52we can really
125. 4:54see some strange artifacts
126. 4:56and let's switch to our lego set
127. 4:59and um i did a color space transform
128. 5:02from
129. 5:04black magic white gamma to sony s-log
130. 5:08i applied the lut everything looks fine
131. 5:12but if i change the contrast
132. 5:15um just to contrast before the lut
133. 5:18we can
134. 5:20spot here those
135. 5:22magenta
136. 5:24colors in the yellow highlights
137. 5:27and if i adjust the curves
138. 5:30we can make it more visible and it's
139. 5:33pretty obvious that
140. 5:35yeah that that this is not perfect
141. 5:39and here's another example
142. 5:42and this is without the lut
143. 5:45and this is a color space transformed to
144. 5:47sony s log
145. 5:49we applies a lot and
146. 5:53at the first glance it is not really
147. 5:55visible
148. 5:56but if we look very closely we can see
149. 5:59the
150. 6:01magenta
151. 6:02in the highlights
152. 6:04and if i increase the contrast here
153. 6:09um
154. 6:10yeah it's really really visible
155. 6:14yeah so let's move on to the next slot
156. 6:17lut number three
157. 6:22i enable the lut and we can immediately
158. 6:24spot the hard edges in the green area
159. 6:30i switch to our test image and this is
160. 6:32without the lut
161. 6:35and now i will enable the lot
162. 6:43these slots you've seen here came from
163. 6:45very popular and expensive lut packs and
164. 6:48the people behind those slots call
165. 6:50themselves professionals and name
166. 6:52clients like netflix sony universal nike
167. 6:55on their websites
168. 6:57but none of these i've tested so
169. 6:59far are professional quite the opposite
170. 7:02next i want to talk about the
171. 7:04limitations of the test image by showing
172. 7:06you some real professional luts designed
173. 7:09for red color space
174. 7:11in the first node i transform the color
175. 7:13space to red
176. 7:15and at the first glance everything looks
177. 7:17fine
178. 7:18we see a nice gradient vertically and
179. 7:20between our u's
180. 7:22however if i push the contrast further
181. 7:25we now notice some artifacts
182. 7:27and this is not because it is a bad lut
183. 7:30but because our test image only covers
184. 7:32the rgb color space
185. 7:34we can apply a color space transform to
186. 7:37red color space but it is not the same
187. 7:40like capturing data coming from a real
188. 7:42red camera so keep in mind that the test
189. 7:46image has limits and not every artifact
190. 7:48we see means that the lut is bad
191. 7:51we have to be really careful with
192. 7:53testing and judging a lot based on test
193. 7:55images but hopefully this video helps to
194. 7:58understand that the test image can be
195. 8:01very helpful
196. 8:02a test image allows us to get a first
197. 8:04impression of a lot
198. 8:06and after that we can dig deeper into
199. 8:09the area that looks weird
200. 8:11by the way the test images and the lego
201. 8:13footage are available for download on my
202. 8:15website for free
203. 8:18you can find the link in the description
204. 8:20of this video
205. 8:21so that's it please comment i really
206. 8:23love to hear your thoughts on the topic
207. 8:26have a nice day and see you next time