First presented at GDC2018

1. WCG in GTSPORT
Hajime UCHIMURA / Polyphony Digital Inc.
uchimura@polyphony.co.jp
2018/02/28

2. Wide color gamut(WCG) in GTSPORT.
• “True wide color” is used in GTSPORT.
• Rendering on the Rec.2020 color space.
• Textures are stored in Rec.2020 color space.
• Car paints are measured in full spectrum.

3. Benefits of WCG
Realistic rendering results.
Smooth color after heavy post process.
Future proved.

4. To achieve this, we created:
Tone map to solve color saturation.
Color management/calculation system.
HDR photograph workflow.
Custom JPEGXR texture codec.

5. Results from
GTSPORT

10. Quite good, isn’t it? 

11. “Scapes” • Realistic car model rendered
over a background photograph.

13. Brand central
•Real car +
real color +
real scenery +
real time.
•Based on:
• Accurate car color
• Ultra high quality car model

14. How we did it.

15. Things already done:
• Car paints measured in full spectrum.
• Background pictures shot in RAW.
• We already had “WCG” source!
• Even before HDR TV

16. Basic strategy
Render
everything in
HDR+WCG.
Shrink it for
SDR TV.

17. Problem occurred.

18. A usual picture in Rec.709.

19. Turns saturated.
Caused by simple color conversion.

20. Saturation must be solved.
• Expensive cars are vivid!

21. “Rec.2020”

22. “Rec.709”

23. Out of gamut
colors.

24. 100 nits of
Rec.2020
• Rec.2020 colors,
simply converted to Rec.709.
• Rendered in sRGB

25. 200 nits

26. 1000 nits.

27. Gamut mapping
required.

28. Ideas not used
• Tried so many ideas.
• Tonemap after color conversion.
• Luminance tonemap.
• HSV, Yxy, YCoCg, YUV space.

29. Yxy bleach is
not natural.
Ideas not used(2)

30. Our solution:
• Use tone map as gamut map.
• Tonemap before color conversion.

31. 1.660227 −0.587547 −0.072839
−0.124554 1.132926 −0.008349
−0.018155 −0.100603 1.118998
Linear Rec.2020 HDR tone map HDR
SDR tone map Rec.2020 to Rec.709 SDR

32. Tone map?

33. S-Shaped
Function.

34. Limits
lightness.

35. With & w/o tonemap, 100 nits

36. 200 nits

37. 500 nits

38. “GT Tonemap”
• Linear middle section.
• Contrast adjustable toe.
• Smooth shoulder.
• Variable peak.
• https://www.desmos.com/cal
culator/et1qmcg10s

39. “Hue shifting”
• With this tonemap operator, hue shifts in bright part.
• Solutions needed… 

40. But wait…

41. Hue shifts even in real! Shot on Nexus5X

42. “Hue shifting”

43. “Looks natural”
• Problem solved

44. HDR/SDR compatibility.
• The majority are SDR.
• SDR TV user are very important!

45. HDR/SDR with “GT Tonemap”
• Variable peak brightness design.
• Toe & mid same shape on both HDR/SDR.

46. 100 nits
peak
(for SDR)

47. 250 nits
peak

48. 1000 nits
peak

49. SDR boost.
• SDR TVs are brighter than HDR TV.
• Image is enhanced.
• Measured and approximated it.
• sRGB 1.0 = 250 nits, by our approx.

50. Darken SDR? Brighten HDR?
• In GTSRPOT, we darked SDR.
• SDR linearity recovered, looks more realistic.

51. WCG assets.

52. Car paints
Measure car paint in full spectrum.
Convert spectrum to Rec.2020 with CIE1931
CMFs.
Fit BRDF parameter with color samples.

53. BRDF fitting sample
• Smooth BRDF is recovered from
discrete sample below.

54. Capturing photos in WCG.
• We used ILCE-A7 series DSLR.
• Measured color matrices with
Macbeth chart and high CRI LED light.
• Created in-house HDR tool with
measured color matrices.

55. In-house HDR tool.
• “ScapesMixer”.
• Based on Debevec97[1] and Mitsunaga99[2].
• Designed to process huge amount of pictures.
• It has panorama stitcher built in.
[1] Paul E. Debevec and Jitendra Malik. Recovering High Dynamic Range
Radiance Maps from Photographs. In SIGGRAPH 97, August 1997.
[2] Radiometric self calibration, CVPR99.

56. Server storage.
• Radiance HDR format
• Paired with metadata file.
• “hdrmix”
• In-house tool refers this metadata file.
• Photoshop 2017 breaks HDR pixel value.
• Fixed in Photoshop CC2018.

57. Disk package.
• Compress with JPEGXR.
• Rec.2020 is used instead of scRGB.
• To optimize speed, we developed custom JPEGXR codec.
• Fastest JPEGXR encoder/decoder in the world, maybe.

58. Conclusion
WCG has a lot of benefits!
I recommend HDR and WCG for photo realistic games.
With HDR 1st workflow, SDR image also will be better!

59. • HDR理論と実践
https://d65.xyz/?p=46
• シリコンスタジオによる
HDR出力対応の理論と実践
https://www.siliconstudio.co.jp/rd/presentations/
• Advanced Techniques and Optimization of
HDR Color Pipelines
https://gpuopen.com/gdc16-wrapup-presentations/
• HDR COLOR GRADING AND DISPLAY IN FROSTBITE
https://www.ea.com/frostbite/news/
high-dynamic-range-color-grading-and-display-in-frostbite
References