Decode to Encode: Master Complex Concepts Faster, Bridge Gaps and Be the Expert in Video Coding by Avinash Ramachandran

Author:Avinash Ramachandran [Ramachandran, Avinash]
Language: eng
Format: azw3, epub
Tags: VIDEO COMPRESSION, MPEG, HEVC, VIDEO CODING, ENCODING, H264, H265, VP9, AV1, DECODING, ML, MACHINE LEARNING
Publisher: Avinash Ramachandran
Published: 2018-11-27T16:00:00+00:00

Figure 60: A 16x16 block of residual values after prediction.

It should be noted that quantization is an irreversible process, meaning there is no way to exactly reconstruct the signal input from the quantized values. To illustrate this concept, let us now perform the reverse operations just as the decoder would do when it receives the quantized signal in Figure 62.

Figure 61: The 16x16 block after undergoing a 16x16 transform.

Figure 62: The 16x16 block after undergoing quantization.

Figure 63 shows the 16x16 block after the process of inverse quantization. This is followed by Figure 64 that shows the final reconstructed residual values at the decoder after inverse transform. While these values clearly show patterns and are a fair approximation of the original 16x16 residual block in Figure 60, it’s nowhere near an identical representation of the input source.

The above operations were performed at higher QP, upwards of 40. This introduces significant quantization of the transformed values, as we observe in Figure 62. Let us now illustrate how this QP value affects the results above by doing the same operations at around QP 30 and also at around QP 20. This is shown in Figures 65 and 66, below.

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