Clarifying High Dynamic Range (HDR)

Transcription

1 Clarifying High Dynamic Range (HDR) PART OF SMPTE S MONTHLY EDUCATION SERIES Sponsored by: SMPTE Educational Webcast Sponsors Thank you to our sponsors for their generous support of SMPTE and SMPTE s Monthly Webcasts: 2 1

2 SMPTE Monthly Education Webcast Series Series of monthly 1-hour online, interactive webcasts covering a variety of technical topics Free professional development benefit for SMPTE members Sessions are recorded for member viewing convenience. 3 Views and opinions expressed during this SMPTE Webcast are those of the presenter(s) and do not necessarily reflect those of SMPTE or SMPTE Members. This webcast is presented for informational purposes only. Any reference to specific products or services do not represent promotion, recommendation, or endorsement by SMPTE 4 2

3 Today s Guest Speaker Joseph Slomka Vice President and Principal Color Scientist FotoKem 5 Your Host Joel E. Welch Director of Education SMPTE 6 3

4 Introduction This presentation will go over 3 main HDR topics Effects of HDR display on the perception of resolution and depth Experiences in support grading a HDR theatrical and a HDR video How HDR can affect the artistic process 7 What is HDR HDR is a technology that allows more more dynamic range than current displays. It allows for uncrushed blacks and unclipped whites 8 4

5 Introduction This is going to cover captured motion pictures Much of this will apply, but differently, to Computer Graphics and VFX 9 Benefits of HDR Acquisition Captures a more complete version of the scene Display Reproduces greater detail More natural image appearance* The ability to have greater local contrast The ability to have greater overall contrast Increased perception of color 10 5

6 Goals Connect the technical, scientific and artistic 11 A little about light 6

7 Stops Stops are a way of describing an amount of light One stop represent a doubling of light Increasing one stop doubles the amount of light Decreasing one stop halves the amount of light They have been used in photography because relevance to the process and have been adopted by digital cinematography stops = log 2 (linear _light) 13 How Much DR is HDR? Acquisition Display 14 7

8 How Much DR is HDR? Acquisition Film Greater than 14 stops (Kodak 5219) A good starting point for acquisition Display DCI DCP Around 10 stops at rated contrast ratio(2000:1, 1200:1) More than that is where HDR begins 15 Human Perception and Dynamic range TYING TO GETHER HDR, UHD, AND HFR 8

9 HDR, 4K,HFR: How They Fit Together Higher dynamic range allows for more image contrast The higher contrast allows for greater perception of detail Higher luminance increases the perception of flicker Higher frame-rate reduces flicker Each of these technologies increases the value of the other creating better pixels 17 Visual Limits Dynamic range of vision stops Simultaneous dynamic range stops 18 9

10 Contrast, Resolution and HDR Ability to see contrast dependent on brightness Higher contrast between pixels allows for greater perception of detail 19 HDR and Resolution Contrast sensitivity function Contrast is a key part of identifying detail 20 10

11 Contrast and Resolution Contrast and Resolution Contrast as Resolution 11

12 Contrast Sensitivity Function Attribution By: Star Whitt-Frousiakis Located at: commons.wikimedia.org/wiki/file:contrast_sensitivity_vs._spacial_frequency.png 23 Contrast Sensitivity Changes With Brightness You become more sensitive to high frequency detail in brighter light Another way to say it The brighter an image is the less contrast you need to see detail From cd/m^2 there is a significant change

13 Contrast and Depth Perception Stereo images are only part of seeing depth 25 Contrast and Depth 13

14 Ways Depth is Perceived Accommodation Convergence Binocular Parallax Monocular Movement Parallax Retinal Size Linear Perspective Texture Position Aerial Perspective Shades and Shadows 27 Ways Depth is Perceived Accommodation Convergence Binocular Parallax Monocular Movement Parallax Retinal Size Linear Perspective Texture The closer we are to an object the more detail we can see of its surface texture. Objects with smooth textures are usually interpreted being farther away. This is especially true if the surface texture spans all the distance from near to far. Position Aerial Perspective Shades and Shadows The location of a light source and see objects casting shadows on other objects bright objects seem to be closer to the observer than dark ones

15 Flicker and Luminance Flicker can be described with temporal sensitivity As average luminance increases so does flicker sensitivity Color is adaptive, flicker is not 29 Questions ASK AWAY 30 15

16 HDR and the artistic process A Different Look How can it help the story? How can it hurt? 32 16

17 Trickshot Gale Tattersall - Director of Photography Curtis Clark ASC HDR and ACES technical consultant Senior Colorist John Daro 33 Trickshot Designed to show off the C300MKII Ground up HDR Onset HDR mastering ACES 1.0 Pre-release NAB delivery 34 17

18 Onset with HDR Trick Shot Preproduction Canon monitor 400nit Available this month Using Canon raw 35 SDR Grade An experienced DP and Colorist leaves little chance for unnecessary drama 36 18

19 Secret HDR Grade Secret 2000 nit 4k prototype display with SMPTE 2084 encoding Graded on the show floor using ACES 1.0 on the Mistica Separate grade on selected shots Tradeshow goodness 37 Notes HDR monitoring on set with 400 nit HDR display HDR presentation and final grade on 2000 nit Sense of depth Texture 38 19

20 San Andreas Director of Photography Steve Yedlin Senior Colorist - Walter Volpatto Dolby Technical Lead - Thaddeus Beier Dolby Assistant Colorist -Rick Taylor 39 Feature Color Correction San Andreas Theatrical Master Video Master 108 nits Dolby Vision 4000 nits 40 20

21 San Andreas Acquired with ARRI Alexa Using custom color science from Steve Yedlin. 41 Strong Vision The photography was captured with a specific vision The DCP grade was made in a way similar to a traditional film grade Very few windows, highlights were allowed to blow out if that is how they fell on the rendering 42 21

22 HDR Color Setup The look for the 2d version had a directed artistic vision Preserving that look and mapping it to HDR was central to the design process The HDR lookup table was set so that everything below diffuse white was left untouched. Above diffuse white the lut was stretched to show additional highlight detail, then preserving the original roll off No access to an HDR display before the session 43 HDR Color Setup Results The DCP material was graded in a way that did not constrain the dynamic range and was ideal for HDR Many scenes were completely unchanged Many scenes were mostly unchanged 44 22

23 Unexpected Results and Notes Technically the look of the film was largely preserved Most of a frame is composed below diffuse white The notes from the grading colorist are nuanced 45 Consistent Pixels : Inconsistent Feel Ideally the state of adaptation would remain constant over the picture with the highlights being perceived as specular detail This didn t hold up everywhere Vistas, cityscapes, outdoors, fire and machines were amazing Scene with sufficient highlight caused faces to feel dim Vision adjusted to specular light, not nominal This was true even with just 1 more stop of range Even a small amount of highlight in a scene caused the issue Technically correct, artistically incorrect 46 23

24 Inconsistent Look Unwanted details Lights become directional New light shapes 47 Colorist Notes After the project was delivered 4 different paths were identified: 1. Start from scratch No tone map or trims 2. Stretch the signal Extend the contrast, blacker blacks, whiter whites 3. Raise exposure Make everything brighter 4. Combination Make it brighter with limited additional highlights 48 24

25 My Notes It all makes sense once you see it The way we see and the way we create are not the same Cinematography is concerned about ratios We should be as well Different results Trickshot vs San Andreas 49 Questions ASK AWAY 50 25

26 Problems in HDR Exposure and Dynamic Range Exposure- Brightness or darkness of a scene Dynamic range- the range of available light 52 26

27 No Agreed Upon Image Parameters There is no standard for black, white or grey in HDR This is a problem 53 This is One of the Two Big Headaches A lot of high tech solutions are being developed to deal with this issue No desire to limit all masters to the smallest dynamic range No display reaches the highest value of 10,000 Capture becomes extremely challenging 54 27

28 Wide Variety in Display Performance Display peak white values vary greatly cd/m^2 Black levels as well LCD to OLED blacks 55 Current TV s Have a Lot of Variability Current home TV s have a lot of variability Target master luminance is typically 100 nits Homes can have nits However dynamic range is fixed 56 28

29 Won t someone think of the Children Editors Advertisers? If exposure values vary to much editorial becomes impossible Selling ads also becomes difficult viewing an SDR ad in HDR content could look very different 57 Picking a Point, nit Picking Cinematographers already solved this issue Build the image around people Dynamic range built around that 58 29

30 Good HDR comes from artists Although the cameras capture HDR it needs artistic direction Post conversion of HDR is more difficult than starting with HDR 59 Questions ASK AWAY 60 30

31 The Wild West of HDR Several Specifications, But No Standards Competing specifications mean no standards 62 31

32 Competing Formats BBC Technicolor Dolby Phillips 63 No Perfect Answer Each solution comes from a specific viewpoint and solves specific issues The rooms I am in mention Dolby and BBC as the main proposals I may just be in the wrong rooms 64 32

33 BBC Attempts to be compatible with existing monitors, TV and distribution Keeps the midtone and shadows the same as rec709 Adjusts highlights for the extra dynamic range No-metadata 65 Dolby A new approach not backwards compatible Based on decades of vision research Fully designed end to end Provide SDR compatibility mode PQ encoding Uses metadata to provide display mapping 66 33

34 Technicolor Encoding curve with parameters Uses metadata Supports a variety of encoding scenarios 67 Philips Parameter based HDR Uses HDR grade as starting point Tone-mapping and metadata produce the Standard Dynamic range 68 34

35 Blu-ray Also Complicates This As part of the Blu-ray HDR specification there is a limit to an APL of 400 nits 69 Q&A Verbal Questions Take Priority! Joseph Slomka Vice President and Principal Color Scientist FotoKem Joel E. Welch 70 35

36 SMPTE Education Webcast Series Sponsors Thank you to our sponsors for their generous support of SMPTE and SMPTE s Monthly Webcasts: 71 36