Chroma from Luma (CfL) in AV1

Presented at the VideoLan Dev Days 2017. In this presentation I give an overview of CfL In action by describing the 3 steps required to build the Chroma from Luma prediction.
https://vimeo.com/269083327

Transcript

1. Chroma from Luma (CfL) in AV1 VideoLan Dev Days 2017 Luc Trudeau @trudluc David Michael Barr @barrbrain Alliance for Open Media Working Group, September 2017 Mozilla and the Xiph.Org Foundation You can download these slides from https://tinyurl.com/cfl-vdd2017 This work is licensed under a Creative Commons Attribution 4.0 International License. 1
2. What is Chroma from Luma? IIntra prediction tool Only available to chroma planes (uv_mode) Predicts chroma using coincident-reconstructed luma pixels Adopted in AV1 (Not on by default yet (working on it)) 2
3. What does it do? Builds prediction based on reconstructed luma pixels Signals scaling factors (Different from LM Mode (HEVC) and Thor) 3
4. CfL In Action 4 Chroma DC_PRED CFL_PRED Scaling factors (-0.25, 0.125) Height = 1.1 cone hat
5. CfL in Actions 3 Steps 1. Compute Luma AC contribution 2. Scale Chroma Plane 3. Add Chroma DC_PRED 5
6. CfL in Action Step 1: Compute AC Contribution 6 Subsample Average 202 Reconstructed Luma Pixels AC Contribution
7. CfL in Action Step 2: Scale Chroma Planes 7 AC Contribution α Cb = -0.25 α Cr = 0.125 Scaled
8. CfL in Action Step 3: Add Chroma DC_PRED 8 Scaled Values Chroma DC_PRED CfL Prediction
9. UV Mode Selection Example (https://goo.gl/6tKaB8) CFL_PRED 17% DC_PRED 44.36% SMOOTH_PRED 4.85% TM_PRED 7.98% 9 Ohashi0806shield.y4m QP = 55
10. Subset1 Objective-1 fast Results (AWCY High Latency) PSNR PSNR-HVS SSIM CIEDE20001 PSNR Cb PSNR Cr MS SSIM Average -0.46 -0.29 -0.33 -4.65 -12.99 -10.84 -0.32 Ref : https://arewecompressedyet.com/?job=master%402017-07-26T10%3A40%3A11.180Z&job=cfl-baseline%402017-07-29T00%3A04%3A47.130Z 10 1. CIEDE2000 is the only metric that combines luma and chroma plane (The distance measured is more perceptually uniform) PSNR PSNR-HVS SSIM CIEDE20001 PSNR Cb PSNR Cr MS SSIM Average -0.43 -0.42 -0.38 -2.41 -5.85 -5.51 -0.40 1080p -0.32 -0.37 -0.28 -2.52 -6.80 -5.31 -0.31 1080p Screen -1.82 -1.72 -1.71 -8.22 -17.76 -12.00 -1.75 360p -0.15 -0.05 -0.10 -0.80 -2.17 -6.45 -0.04 720p -0.12 -0.11 -0.07 -0.52 -1.08 -1.23 -0.12 Ref: https://arewecompressedyet.com/?job=master%402017-09-13&job=cfl-inter%402017-09-13T14%3A13%3A13.918Z
11. Awesome for Gaming (Twitch dataset) 11 https://arewecompressedyet.com/?job=no-cfl-twitch-cpu2-60frames%402017-09-18T15%3A39%3A17.543Z&job=cfl-inter-twitch-cpu2-60frames%402017-09-18T15%3A40%3A24.181Z
12. Chroma from Luma in AV1 What’s next? Optimizations SIMD / Neon Future Work 4:2:2 Support CfL in Inter (In another codec) Design document available at https://tinyurl.com/cfl-design-doc 12 Patches Welcome!