Differentiable JPEG: The Devil is in the Details (2309.06978v4)

Abstract: JPEG remains one of the most widespread lossy image coding methods. However, the non-differentiable nature of JPEG restricts the application in deep learning pipelines. Several differentiable approximations of JPEG have recently been proposed to address this issue. This paper conducts a comprehensive review of existing diff. JPEG approaches and identifies critical details that have been missed by previous methods. To this end, we propose a novel diff. JPEG approach, overcoming previous limitations. Our approach is differentiable w.r.t. the input image, the JPEG quality, the quantization tables, and the color conversion parameters. We evaluate the forward and backward performance of our diff. JPEG approach against existing methods. Additionally, extensive ablations are performed to evaluate crucial design choices. Our proposed diff. JPEG resembles the (non-diff.) reference implementation best, significantly surpassing the recent-best diff. approach by $3.47$dB (PSNR) on average. For strong compression rates, we can even improve PSNR by $9.51$dB. Strong adversarial attack results are yielded by our diff. JPEG, demonstrating the effective gradient approximation. Our code is available at https://github.com/necla-ml/Diff-JPEG.

• The paper presents an improved surrogate model that captures unmodeled JPEG quantization details for differentiability.
• It achieves a 3.47 dB average PSNR boost and up to 9.51 dB improvement under strong compression scenarios.
• The method delivers more effective gradients for adversarial attacks, enhancing integration into neural network pipelines.

Differentiable JPEG: The Devil is in the Details

The paper entitled "Differentiable JPEG: The Devil is in the Details" presents a novel approach to integrating JPEG compression into deep learning pipelines by approximating the JPEG process differentiably. JPEG, being a ubiquitous image compression standard, inherently lacks differentiability due to its discrete nature, which poses a significant limitation for its integration with gradient-based learning systems such as deep neural networks. Several attempts have been made to address this challenge, focusing primarily on constructing differentiable substitutes for JPEG components. This paper improves upon these by addressing previously unmodeled aspects and offering enhanced performance.

The authors conduct a thorough review of existing differentiable JPEG approaches, categorizing them into three types: straight-through estimators (STE), surrogate models, and noise-based methods. While STE assumes constant gradients through non-differentiable functions, surrogate models employ differentiable approximations, and noise-based methods introduce data perturbations emulating JPEG artifacts. The novel contribution of this paper lies in the development of an improved surrogate model that captures critical unmodeled details, such as quantization table bounds and clipping in the image range, which existing models tend to neglect.

In terms of numerical performance, the proposed method significantly surpasses existing differentiable JPEG implementations. On average, it offers a PSNR improvement of 3.47 dB, and this enhancement extends to a remarkable 9.51 dB under strong compression scenarios, indicating its superior fidelity to the non-differentiable reference JPEG.

The paper also provides empirical evidence through adversarial attack experiments to assess the quality of gradients derived from the differentiable JPEG function. Here, the new method produces more effective adversarial examples than its predecessors, demonstrating its utility for tasks reliant on gradient flow.

The implications of this research are far-reaching. Practically, it facilitates the integration of JPEG compression into diverse AI applications where backward gradients matter, improving upon tasks like data hiding, adversarial attacks, and deepfake detection. Theoretically, it sets a benchmark in the differentiation of traditionally non-differentiable processes, expanding the scope of automated differentiation in machine learning.

Future developments in this field might focus on further improving the fidelity and efficiency of differentiable JPEG models. Additionally, adapting this differentiability framework to other compression standards could optimize their employment in neural network training, potentially enabling end-to-end learning systems to natively incorporate compression artifacts. As a consequence, studies like this underscore the vital significance of bridging traditional data processing methods with artificial intelligence, ensuring computational efficiency and enhanced performance.