TECHNICAL FIELD

The present principles relate to adaptive resolution coding (ARC) of video images.

BACKGROUND

Recent deployment of Ultra High Definition (UHD) video content at formats of 3840×2048, and the forthcoming UHD-2 video format of 7680×4320p at 100/120 Hz has caused a need for video compression tools and systems that can manage such very high definition pictures.

In addition, the advent of Video on Demand (VOD) and Over the Top (OTT) applications, as well as an increase in video content exchanged through video streaming applications, Adaptive Resolution is foreseen as a new and challenging requirement of future video codecs.

Adaptive resolution coding in the High Definition Video Coding (HEVC) standard means adapting resolution dynamically in response to circumstances, without inserting Instantaneous Decoder Refresh (IDR) frames. Gains have been shown to be between 6.9-7.4% when using ARC compared to inserting an IDR frame. Some studies reported gains between 3-30%, depending on the original frame size and configuration, using one empirical resolution switch selection method.

In a real use case, resampling to reduced resolution has been used to facilitate sufficient coding efficiency in low bitrate applications. A first prior method reported an average Blu-ray Disc (BD) rate reduction of about 10% (up to 15%, 27.1%, and 19.4% in Y, U, V respectively) using 4K and 8K video content with a modified version of the HEVC reference software

When Adaptive Resolution Coding is implemented in a video codec, two main issues may be encountered.

First is precision loss. The lack of precision in calculations performed during upsampling or downsampling operations performed during resizing to align the reference picture resolution with the current picture size introduces some losses. The upsampling and downsampling processes use additional rounding operations with potential loss of information that accumulates with the filtering and rounding operations of the Motion Compensation (MC) filters.

The second issue is an increase in memory requirements. The decoder picture buffer (DPB) can contain all possible resolutions, which can increase the decoder memory requirements.

Another prior approach has shown that one can reduce both of these limitations by combining resizing and motion compensation together. However, the combined resizing and motion compensation processing is obtained through the use of filters with increased number of taps that increases the calculation load and can reduce the benefits of this combined approach.

SUMMARY

These and other drawbacks and disadvantages of the prior art are addressed by the present principles, which are directed to a method and apparatus for combining Adaptive Resolution Coding and Adaptive Internal Bit Depth Increase.

The present principles comprise specifying an internal bit depth increase (IBDI) associated with potentially resized reference pictures, independent of the regular bit depth of the decoded and reconstructed pictures. The resized IBDI parameter can be adapted per picture or per region. An advantage of these principles is an improvement in video coding efficiency by increasing the precision of resized pictures when Adaptive Resolution Coding is used.

According to one aspect of the present principles, a method for adaptive resolution coding is provided. The method comprises resizing an image to be used as a reference picture, and increasing the bit depth of the resized image to a greater precision than before resizing. The method further comprises storing the resized, increased bit depth image, and performing motion compensation on a current image using the stored, resized image as a reference.

According to another aspect of the present principles, an apparatus for adaptive resolution coding is provided. The apparatus comprises a processor to resize an image to be used as a reference, and further comprises shift circuitry to increase the bit depth of the resized image to a greater precision than before resizing. The apparatus also comprises memory to store the resized, increased bit depth image, and motion compensation circuitry operating on a current image and using the stored, resized image as a reference.

In one advantageous embodiment, the previously mentioned method and apparatus are implemented in an encoder.

In another advantageous embodiment, the previously mentioned method and apparatus are implemented in a decoder.

In yet another advantageous embodiment, the previously mentioned method and apparatus are implemented using bit depth information signaled in a bitstream.

In yet another advantageous embodiment, the previously mentioned method and apparatus are implemented and an increase in bit depth of resized images is performed only for images of a particular resolution.

In yet another advantageous embodiment, the previously mentioned method and apparatus are implemented and an increase in bit depth is performed on a per picture basis.

In yet another advantageous embodiment, the previously mentioned method and apparatus are implemented and a bit depth of a reference image varies per region in the reference image.

