A video coding pipeline is provided that can accommodate high dynamic range (HDR) and wide color gamut (WCG) content at a fixed bitrate. The video coding pipeline relies on separate chromaticity and luminance-specific transforms in order to process image content. Image content may be converted into a nearly perceptually uniform color space for coding in constant luminance. Moreover, chromaticity transforms are utilized which reduce coding errors in the chroma components (at the fixed bitrate) by enlarging the distribution of code words for compression.
TECHNICAL FIELD(1) The present disclosure relates generally to video coding.DESCRIPTION OF THE RELATED ART(2) Interest in distributing video or other visual content having high dynamic range (HDR) and wide color gamut (WCG) is growing due to its ability to provide a viewing experience that is more enhanced when compared to conventional standard dynamic range (SDR) and standard color gamut (SCG) content. SDR content typically has a brightness of e.g., 0.1 to 100 nits, a range that is significantly less than that which the human eye can see in real life. However, footage that is filmed or re-mastered in HDR and WCG contains more information, which in turn necessitates larger file sizes along with increased bitrate.BRIEF SUMMARY OF THE DISCLOSURE(3) Various embodiments are directed to providing better content (e.g., picture) quality at a fixed bitrate through the use of a constant luminance coding pipeline in which image content is converted into a nearly perceptually uniform luminance/chrominance (Y/U′V′) color space. Additionally, various chromaticity transforms (performed using a dedicated chromaticity transform separate and distinct from the luminance transform) are disclosed for use in the coding pipeline.(4) In accordance with one embodiment of the present disclosure, a computer-implemented method comprises converting an additive color model signal into a uniform color space signal having chromaticity components and a luminance component. The computer-implemented method fu
1. A computer-implemented method, comprising: converting an additive color model signal into a uniform color space signal having chromaticity components and a luminance component; transforming the chromaticity components by applying a chromaticity-specific transform to the chromaticity components, wherein the chromaticity-specific transform maps a main triangular representation of the chromaticity components in the uniform color space to a four-sided polygonal representation of the chromaticity components in the uniform color space; transforming the luminance component by applying a luminance-specific transform to the luminance component; quantizing the transformed chromaticity components and luminance component; and encoding the quantized chromaticity components and luminance component.
15. A non-transitory computer readable medium having computer executable program code embodied thereon, the computer executable program code configured to cause a processor to: decode quantized color and brightness components of an input bitstream carrying an image signal represented by a first color space model having brightness and color components; dequantize the quantized color and brightness components; apply a first inverse transform to the dequantized color component, wherein the first inverse transform maps a four-sided polygonal representation of the color component in the first color space model to a triangular representation of the color components in the first color space model; apply a second inverse transform to the dequantized brightness component separately from applying the first inverse transform to the color component; and convert the image signal represented by a first color space model into that represented by a second color space model, the second color space model being an additive color space model.
19. A system, comprising: a processor comprising: a converter, a first transformer, an opto-electrical transfer function, and an encoder; a non-transitory computer-readable medium coupled to the converter, the first transformer, the opto-electrical transfer function, and the encoder, the non-transitory computer-readable medium having computer executable program code embodied thereon, the computer executable program code configured to cause a processor to: convert an image signal represented by a first color space model into that represented by a second color space model having brightness and color components using the converter; apply a first transform to the color component using the first transformer, wherein the first transformer maps a triangular representation of the color components in the second color space model to a four-sided polygonal representation of the color components in the second color space model; apply a second transform to the brightness component using the encoder separately from applying the first transform to the color component; quantize the transformed color and brightness components using the quantizer; and encode the quantized color and brightness components and output a bitstream using the encoder.