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Picture Quality Improvement Schemes for HDTV Applications

Picture Quality Improvement Schemes for HDTV Applications. Hiroshi Shimamoto Kunal Ghosh. Outline.  Overall Project Motivation Improve picture quality by minimizing colour aliasing effects Project Objectives o Explore new color filter arrays for increasing resolution

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Picture Quality Improvement Schemes for HDTV Applications

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  1. Picture Quality Improvement Schemes for HDTV Applications Hiroshi Shimamoto Kunal Ghosh

  2. Outline  Overall Project Motivation • Improve picture quality by minimizing colour aliasing effects • Project Objectives o Explore new color filter arrays for increasing resolution o Explore new demosaicing algorithms for color interpolation  Project Approach o Simulate images with new CFA and examine H resolution o Suppress V colour aliasing using vertical O-LPF • Simulate images with new demosaicing algorithm • Propose Directions for Future Work

  3. Standard Bayer CFA RGB CFA Bayer’s pattern Nyquist frequencies are different between G and B/R

  4. New 4x2 CFA (Shimamoto et. al 2006) G B R G = + … G R B G Nyquist’s frequencies are same But Optical LPF for vertical direction will be needed

  5. Simulations with ISET • ISET 2.0 was used for all the simulations • The simulation routine was setup as follows: • Scene was created (e.g., ‘frequencyOrientation’, ‘slantedBar’) • Scene FOV was matched to sensor FOV • Optical image was created using typical optics, optional O-LPF • Sensor image was created with CFA option parametrized • Demosaiced image was computed using parametrized scripts • Analyses: • Plot MTF in sensor image regions with CFA, O-LPF combinations • Plot chromaticity of various regions in demosaiced images • Evaluate performance using MTF and chromaticity plots

  6. Bayer CFA Simulations (1) No diffuser (all pass filter) 256x256 pixel count sensor Bayer CFA Bilinear demosaicing Demosaiced image Scene Entire image Horizontal Vertical Scene Chromaticity

  7. Bayer CFA Simulations (2) O-LPF (H, V sd 1pixel) 256x256 pixel count sensor Bayer CFA Bilinear demosaicing Demosaiced image Scene Entire image Horizontal Vertical Scene Chromaticity

  8. 4x2 CFA Simulations (1) No diffuser (all pass filter) 256x256 pixel count sensor New 4x2 CFA Bilinear demosaicing Demosaiced image Scene Entire image Scene Chromaticity Horizontal Vertical

  9. 4x2 CFA Simulations (2) O-LPF (V sd 1pixel) 256x256 pixel count sensor New 4x2 CFA Bilinear demosaicing Demosaiced image Scene Entire image Scene Chromaticity Horizontal Vertical

  10. 4x2 CFA Simulations (3) O-LPF (V sd 2 pixel) 256x256 pixel count sensor New 4x2 CFA Bilinear demosaicing Scene Demosaiced image Entire image Scene Chromaticity Horizontal Vertical

  11. CFA Results Summary  4x2 CFA • Minimized color aliasing (R, G, B) in horizontal direction as expected • Vertical O-LPF reduces colour aliasing, but lowers vertical resolution • 2 pixel diffuser in vertical direction suppresses most of colour aliasing • Explore CFA variations to minimize vertical color aliasing

  12. New Demosaicing Purpose: false color elimination in high spatial frequency B’=(2G+R)/3 R’=(2G+B)/3

  13. New Demosaicing Simulations Demosaiced image Bayer + Bilinear Demosaiced image Bayer + New Demosaic Scene Scene Chromaticity

  14. Color Change Error (future work) No diffuser (all pass filter) 256x256 pixel count sensor New Demosaicing Bilinear demosaicing Demosaiced image Scene Entire image Scene Chromaticity

  15. Conclusions  Colour Filter Arrays • Simulated images with various CFAs and quantified performance • Confirmed better Horizontal resolution with 4x2 CFA • Demonstrated techniques to suppress Vertical colour aliasing • Demosaicing o Simulated new demosaiced images o Suitable for monochrome image but more work needed for color o Some adaptive method should be added  Take-aways • Explored picture quality improvement schemes • Gained insights into understanding CFA variations on images • Proposed a new demosaicing algorithm • Leveraged ISET as a tool for simulations and analyses

  16. Appendix

  17. 3x3 CFA Simulations G B R R G B R G B Demosaiced image O-LPF (V sd 1 pixel) Bilinear 2D demosaiced image O-LPF (V sd 1 pixel) Scene Entire image Entire image Scene Chromaticity

  18. 4x2 CFA Simulations (3) Bayer Convert to HDTV image Using Electrical LPF 4x2 Demosaiced image Once aliasing occurred, It will not recovered electrically

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