Presentation on theme: "with RGB Reversibility"— Presentation transcript:
1 with RGB Reversibility YCoCg:A Color Spacewith RGB Reversibility(FRExt)1st Feb 2006
2 Profiles H.264 has four profiles: Baseline (IP Video phone, Simple streaming)Main Profile (Digital Storage Media, Television Broadcasting)Extended Profile (Streaming video)High Profile (Content contribution, Content distribution, Studio editing, post processing)
3 High ProfileThere are four High Profiles (Fidelity range extensions-FRExt)High Profile is to support the 8-bit video with 4:2:0 sampling for applications using high resolution.High 10 Profile is to support the 4:2:0 sampling with up to 10 bits of representation accuracy per sample.High 4:2:2 Profile is to support up to 4:2:2 chroma sampling and up to 10 bits per sample.High 4:4:4 Profile is to support up to 4:4:4 chroma sampling, up to 12 bits per sample, and integer residual color transform for coding RGB signal.Mainly targeting the HD DVD, Broadcast, Editing, Digital still camera market
5 MacroBlock (MB) structure in 4:4:4 format YCbCr16In 4:4:4 video, luma and both the chroma componentswill have same spatial resolution
6 High Profile Applications using High Profile Use more than 8 bits per sample of source video accuracyUse higher resolution for color representation than what is typical in consumer applications (i.e., 4:2:2 or 4:4:4 sampling as opposed to 4:2:0 chroma sampling format)Perform source editing functions such as alpha blending (a process for blending of multiple video scenes, best known for use in weather reporting where it is used to super- impose video of a newscaster over video of a map or weather-radar scene)Use very high bit ratesUse very high resolutionAchieve very high fidelity – even representing some parts of the video losslesslyAvoid color-space transformation rounding errorUse RGB color representation
8 In 4:4:4 video, FRExt has Residual Color Transform. Keep RGB domain (same depth) for input, output and stored reference pictures and use the forward and inverse color transformations inside the encoder and decoder for processing of the residual data only.Eliminates color-space conversion error without significantly increasing the overall complexity of the system.
9 H.264 Encoder= Residual Color Transform RGB to YCoCg
10 Residual color transform exploits the redundancy among the residual data of each RGB component after intra/inter prediction. The correlation among the color components still exists even after the intra/inter prediction. To decorrelate this redundancy, we apply the YCoCg color transform to the residual data.This scheme can be easily incorporated into the existing JVT specification.This technique achieves better coding efficiency than applying the color transform outside the coding loop as manifested in the simulation results of , .YCoCg color space has improved coding gain relative to both RGB and YCbCr.Y = Luminance componentCo = Orange Chroma componentCg = Green Chroma component
11 YCbCr Color Space There are two problems with this approach. Since the samples are actually represented using integers, rounding error is introduced in both the forward and inverse color transformations.The second is that, because the above transformation was not originally designed for digital video compression, it uses a sub-optimal trade-off between the complexity of the transformation (with difficult-to-implement coefficient values such as and ) and coding efficiency.
12 YCoCg Color Space Forward Color Space Transform Inverse Color Space Transform
13 So encoder/decoder needs only additions and shifts to RGB YCoCg
14 R, G, and B are the residual data and Y, Co, and Cg are the residue transformed data
15 Simulation Results that show the coding gain for Y component in dB Seq.bit rate (Mbps)1040100Analog TVNA11.5Trees and Bicycle0.50.60.8Man in Restaurant0.7Rolling Tomatoes1.2Card TossDinnerThe coding gain using residual color transform for Y component in YCoCg color domain is about 0.5~1.5 db depending on the bit rate.Note: These results are taken from 
16 ConclusionYCoCg color space transformation has three important features:1. Exactly reversible in integer arithmetic. (i.e MSE=0)2. Minimal increase in dynamic range; no increase for Y and only 1 bit increase for Co and Cg.3. Higher coding gain than other color spaces.
20 References JVT document - JVT-I014r3.doc (ftp://standards.polycom.com) JVT document - JVT-L025.doc JVT document - JVT-Q059_L.doc & JVT-Q059_L.xls Soon-kak Kwon, A. Tamhankar, K. R. Rao, “Overview of H.264/MPEG-4 Part10”, Special issue on “ Emerging H.264/AVC video coding standard”, J. Visual Communication and Image Representation, vol.17, 2006 G. Sullivan, P. Topiwala and A. Luthra, “The H.264/AVC Advanced Video Coding Standard: Overview and Introduction to the Fidelity Range Extensions,” SPIE Conference on Applications of Digital Image Processing XXVII, vol. 5558, pp , Aug H.264 : International Telecommunication Union, “Recommendation ITU-T H.264: Advanced Video Coding for Generic Audiovisual Services,” ITU-T, 2003