Modified Pseudo-Cylindrical Mapping for Spherical Video Compression
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Solution Overview
Problem
Current panoramic image compression methods, such as equi-rectangular and pseudo-cylindrical projections, result in pixel redundancy and distortion, particularly at the poles, leading to inefficient storage and bandwidth usage in Virtual Reality (VR) systems.
Innovation Solution
A modified pseudo-cylindrical mapping process that moves the bottom one-third of the image to the top corners and fills non-effective areas with linear-interpolated pixels, reducing the image size by one-third and minimizing distortion, while maintaining the surface area equivalence to the original spherical image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If equi-rectangular projection is used to map spherical images, then the equatorial region is relatively undistorted, but polar regions experience significant distortion and pixel redundancy
Solution Approach 1:
The patent applies parameter changes by modifying the projection formula from standard equi-rectangular to modified pseudo-cylindrical projection. Specifically, it adjusts the mapping parameters to transform the spherical coordinate system, changing how pixels are distributed across the image plane. This parameter modification reduces pixel density in polar regions while maintaining equatorial undistortion, directly resolving the contradiction between projection precision and pixel quantity.
Solution Approach 2:
The patent implements local quality by applying different projection characteristics to different regions of the spherical image. The modified pseudo-cylindrical projection maintains uniform pixel distribution and minimal distortion in the equatorial region while reducing pixel density and distortion in polar regions. This regional differentiation allows each area to have optimal pixel characteristics for its specific location on the sphere.
2Manufacturing precision
If pseudo-cylindrical projection is used to map spherical images, then polar objects maintain correct area, but the image size cannot be reduced compared to equi-rectangular projection
Solution Approach 1:
The patent applies parameter changes by modifying the projection formula to create a modified pseudo-cylindrical projection that differs from the standard version. Specifically, it adjusts the mapping parameters to enable image size reduction while preserving the area-accurate representation of polar objects. This parameter modification allows the projection to achieve both polar accuracy and compression efficiency.
Solution Approach 2:
The patent extracts and removes redundant pixel information from the projection. By applying the modified pseudo-cylindrical projection, it identifies and eliminates unnecessary pixels in polar regions where the standard projection creates redundancy. This extraction of redundant information enables image compression while maintaining the accurate area representation of polar objects through the modified projection parameters.
3Measurement precision
If higher-resolution cameras are used to capture panoramic images, then image quality improves, but storage and transmission requirements increase
Solution Approach 1:
The patent applies parameter changes through the modified pseudo-cylindrical projection that optimizes pixel distribution for storage efficiency. By changing the projection parameters, it reduces the total number of pixels required to represent the spherical image while maintaining acceptable quality. This parameter modification enables higher-resolution capture to be achieved with reduced data volume requirements.
Solution Approach 2:
The patent implements local quality by optimizing pixel density distribution across different spherical regions. The modified projection allocates pixels more efficiently, providing appropriate resolution in equatorial regions while reducing pixel count in polar regions. This local optimization maintains image quality where needed while reducing overall data volume for storage and transmission.
Data Source
AI summary
A panoramic video stream is compressed. Sinusoidal projection is performed on spherical input images to generate pseudo-cylindrical projection images. A lower-left region and a lower-right region of the image are cut and moved to upper corners of the rectangular bounding box around the pseudo-cylindrical projection image. These upper corners are non-effective areas of default dark pixels with no image pixels. A bottom one-third of the rows of pixels from the image that contained the moved regions are deleted, compressing the image by 33%. Default dark pixels in interface regions between the moved regions and the pseudo-cylindrical projection image are linear interpolated to provide gradual changes in pixel values across the remaining formerly non-effective regions, preventing encoding artifacts caused by abrupt changes in pixel values. Functions may be implemented using lookup tables. Non-focus image areas may be downsampled for additional compression using multi-resolution mapping and adaptive view streaming.