Avid Technology Limited

Markus Weber

Mykola Gerasymenko

DCT-based methods for fixed bit rate, intraframe compression of video are based on the visual quality of the resulting decompressed imagery. In general, this involves assigning an initial bit budget per macroblock of a given video frame, resulting in degrees of compression, i.e., quantization scale factors, that vary among the macroblocks according to their complexity. The scale factors are then adjusted while maintaining the overall frame bit budget to reduce the visibility of artifacts in the decompressed frame. The adjustments may include increasing scale factors for simple macroblocks and reducing scale factors for complex blocks. As compared to traditional DCT-based compression schemes, the described methods may reduce the visibility of compression-related artifacts both in complex and in simple portions of the frame.

Fixed rate intraframe compression and decompression of video based on visual quality

Low bitrate encoding of HDR-coded content with codecs that achieve compression by lowering the precision of encoding can result in significant loss of color fidelity. The problem stems from the logarithmic nature of the HDR encoding and consequent excessive quantization of color components of HDR-coded material. The loss is ameliorated by applying a saturation emphasis function that boosts color values of the HDR-coded material prior to compression. In various implementations the saturation emphasis function is a monotonically increasing function that preferentially boosts lower color values. Following compression and subsequent decompression, the color boost is reversed. In video post-production workflows proxies may be compressed to very low bitrates. For such workflows, the described methods significantly reduce codec-induced color artifacts in the decompressed proxy, thus restoring the ability of editors to make valid technical decisions based on the proxy during post-production.

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Woerth, Germany

Markus Weber