Efficient Image Super-Resolution through Reference-based Quantization

Core Concepts

A novel reference-based quantization method, RefQSR, that exploits image self-similarity to improve the computational efficiency and performance trade-off of existing super-resolution network quantization techniques.

Abstract

The paper proposes a reference-based quantization method, RefQSR, for efficient image super-resolution (SR) networks. The key ideas are:

1. Patch Clustering: RefQSR divides the input image into patches and clusters them into reference and query patches using a trainable patch clustering block called ClustBlock. ClustBlock extracts textural features from the patches and groups them based on similarity.

2. Reference-based Quantization: The reference patches are quantized using high-bit precision, while the query patches are quantized using low-bit precision. A reference-based error refinement (RefER) block is introduced to compensate for the quantization errors of the query patches by leveraging the features from the associated reference patches.

3. Integration with Existing Quantization Methods: RefQSR can be integrated with various existing SR network quantization methods, including fixed-precision (PAMS, DDTB) and mixed-precision (CADyQ, CABM) techniques, to improve their computational complexity and SR performance trade-off.

The experimental results on several SR networks (SRResNet, CARN, ELAN) demonstrate the effectiveness of RefQSR, achieving significant BitOPs savings (up to 76.9%) while maintaining similar or better SR performance compared to the baseline quantization methods.

Stats

SRResNet-DDTB (8bit) achieves 25.89 PSNR with 21.81 BitOPs on the Urban100 dataset.
SRResNet-DDTB (4-3bit) with RefQSR achieves 25.92 PSNR with 2.14 BitOPs, a 76.9% reduction in BitOPs.
CARN-CADyQ (δ-3bit) with RefQSR achieves 25.93 PSNR with 2.20 BitOPs, a 29.7% reduction in BitOPs.
ELAN-DDTB (4-3bit) with RefQSR achieves 25.99 PSNR with 3.47 BitOPs, a 47.6% reduction in BitOPs.

Quotes

"RefQSR selects several representative patches and quantizes them using high-bit precision. Then, the selected patches are assigned as references and used to assist in low-bit quantization of the rest of the patches, called query patches, in an image."
"RefER takes features from a query patch and its associated reference patch as input and fuses them to compensate for quantization errors of the query patch."

Key Insights Distilled From

RefQSR

by Hongjae Lee,... at arxiv.org 04-03-2024

https://arxiv.org/pdf/2404.01690.pdf

Deeper Inquiries

How can the proposed RefQSR framework be extended to handle other low-level vision tasks beyond super-resolution, such as denoising or inpainting

The RefQSR framework can be extended to handle other low-level vision tasks by adapting the patch clustering and reference-based quantization approach to suit the specific requirements of tasks like denoising or inpainting. For denoising, the clustering algorithm can group patches based on noise levels or patterns, allowing the reference patches to guide the denoising process for query patches. In the case of inpainting, the reference patches can be selected based on the surrounding context of missing regions, enabling the network to fill in the gaps accurately. By customizing the clustering criteria and the reference patch selection process, RefQSR can effectively address a variety of low-level vision tasks beyond super-resolution.

What are the potential limitations of the image self-similarity assumption used in RefQSR, and how could the method be further improved to handle more diverse image content

While image self-similarity is a powerful concept utilized in RefQSR for efficient quantization, it may have limitations when dealing with highly diverse image content. One potential limitation is the assumption that patches with similar patterns or structures will benefit from the same quantization precision. In more complex images with diverse textures and content, this assumption may not hold true, leading to suboptimal quantization results. To address this limitation, RefQSR could be improved by incorporating adaptive mechanisms that dynamically adjust the clustering and quantization strategies based on the content complexity of the input image. By integrating adaptive learning mechanisms or incorporating additional image analysis techniques, RefQSR can enhance its ability to handle a wider range of image content effectively.

Can the RefER block be adapted to leverage additional information, such as semantic or contextual cues, to further enhance the quantization error compensation for query patches

The RefER block can be adapted to leverage additional information, such as semantic or contextual cues, by incorporating features that capture higher-level image attributes. For instance, semantic segmentation masks or object detection outputs can provide valuable information about the content of the image, which can be used to refine the quantization error of query patches more effectively. By integrating semantic information into the RefER block, the network can prioritize error compensation in regions of interest or areas with specific semantic relevance. This adaptive refinement mechanism can enhance the overall performance of RefQSR by incorporating contextual cues to guide the quantization error compensation process for query patches.