Signal Processing for Implicit Neural Representations
Dejia XuPeihao WangYifan JiangZhiwen FanZhangyang Wang
Develops an implicit signal processing framework that uses analytical high-order differential operators to perform continuous convolutions, low-level filtering, and high-level classification directly on coordinate-based neural representations without requiring explicit decoding.
Implicit Neural Representations (INRs) have emerged as a powerful way to represent continuous multimedia data, such as images, video, and 3D shapes, using multi-layer neural networks. Unlike standard digital representations that store values on discrete pixel or voxel grids, INRs model data as continuous functions. However, editing and processing these neural signals directly has remained an intractable problem because their parameters are difficult to interpret. Current solutions typically decode the neural representations back into discrete grids before editing them, which destroys their continuous nature, consumes significant memory, and limits resolution.
The main objective of the article is to develop and evaluate a mathematical framework and architecture that can directly modify and process implicit neural representations without converting them into discrete grids. The authors introduce the Implicit Neural Signal Processing Network (INSP-Net) along with its convolutional extension (INSP-ConvNet), establishing that continuous signal transformations can be executed analytically via differential operators.
The authors based their approach on the mathematical insight that spatial gradients of neural networks can be calculated in closed form and naturally preserve translation invariance. They proved theoretically that any continuous convolution filter can be uniformly approximated by a linear combination of high-order differential operators. INSP-Net builds computational graphs of an INR's spatial derivatives and merges them through an inception fusion block, where operator weights can be either hand-crafted or trained on data. To validate this framework, the authors conducted experiments across low-level 2D image tasks (edge detection, blurring, deblurring, denoising, and inpainting), 3D geometry smoothing using signed distance functions, and high-level image classification on benchmark datasets.
The experimental and theoretical findings highlight several key capabilities of the proposed system. First, the mathematical proofs confirm that INSP-Net can approximate arbitrary continuous convolution filters while inherently preserving shift invariance. Second, in low-level image processing, INSP-Net performed competitively with or superior to established baselines; for example, in image denoising, it achieved 24.02 dB PSNR compared to 20.51 dB from a dedicated restoration model, and successfully executed text removal and patch inpainting without explicit masks. Third, the framework effectively smoothed complex 3D surfaces by applying continuous filter operations directly to geometric distance fields. Finally, when evaluating high-level vision, INSP-ConvNet classified implicit representations directly, reaching 88.1% accuracy on MNIST and 62.5% on CIFAR-10, slightly outperforming standard convolutional networks operating on explicit pixel grids (87.6% and 59.5%, respectively) and vastly surpassing direct parameter classifiers (which achieved around 10%).
These findings demonstrate that digital signal processing and deep convolutional operations can occur entirely within continuous implicit domains, eliminating the need to rasterize data into fixed resolutions. This capability helps preserve fine details, avoids resolution-dependent memory overhead, and opens the door to end-to-end processing pipelines operating natively on coordinate-based neural representations.
Organizations developing implicit representation pipelines should consider adopting derivative-based operators to perform filtering, transformation, and semantic extraction directly on continuous models. For future development, engineering efforts should focus on optimizing the numerical stability and memory efficiency of computing high-order derivatives, as well as designing more compact parameterizations to scale multi-layer implicit networks to larger, real-time vision workflows.
While the theoretical results guarantee universal approximation of convolutions, they rely on infinite-sequence approximations, and real-world implementations must truncate derivative orders. Additionally, current experiments rely on per-scene network optimization, and high-order automatic differentiation creates memory and stability bottlenecks that limit deeper cascading. Readers can place high confidence in the proof-of-concept demonstrations across standard vision benchmarks, though scaling to production workloads will require further advances in derivative computation efficiency.
- Paper: Implicit Neural Representations with Periodic Activation Functions, Vincent Sitzmann et al. (2020). This foundational work introduces periodic activation functions (SIRENs) that enable implicit neural representations to accurately model signals and their spatial derivatives, which forms the core mechanism for derivative-based signal processing.
- Paper: Fourier Features Let Networks Learn High Frequency Functions in Low Dimensional Domains, Matthew Tancik et al. (2020). This paper establishes the theoretical foundation for using Fourier feature mappings in coordinate-based MLPs to overcome spectral bias and represent high-frequency continuous signals.
- Paper: DeepSDF: Learning Continuous Signed Distance Functions for Shape Representation, Jeong Joon Park et al. (2019). This work introduces continuous signed distance functions parameterized by neural networks, providing key 3D implicit geometric representations used in spatial filtering and surface smoothing experiments.
- Paper: Occupancy Networks: Learning 3D Reconstruction in Function Space, Lars Mescheder et al. (2018). This paper establishes continuous 3D function-space representation via neural network decision boundaries, pioneering continuous coordinate-based architectures.
- Paper: NeRF: Representing Scenes as Neural Radiance Fields for View Synthesis, Ben Mildenhall et al. (2020). This paper defines the modern continuous implicit neural representation paradigm mapping spatial coordinates directly to signal values via multilayer perceptrons.
- Paper: Learning nonlinear operators via DeepONet based on the universal approximation theorem of operators, Lu Lu et al. (2021). This work establishes the universal approximation theory for learning operators on continuous function spaces, underlying the continuous operator mapping principles used to process implicit signals.
- Paper: Equivariant Architectures for Learning in Deep Weight Spaces, Aviv Navon et al. (2023). This paper directly builds on the challenge of operating over implicit neural representations by proposing equivariant architectures for learning and processing in raw neural network weight spaces.
- Paper: Neural Operator: Learning Maps Between Function Spaces With Applications to PDEs, Nikola Kovachki et al. (2023). This work generalizes operator learning across continuous, infinite-dimensional function spaces independently of grid discretization, extending continuous domain processing concepts.
- Paper: Convolutional Neural Operators for robust and accurate learning of PDEs, Bogdan Raonic et al. (2023). This study advances continuous-discrete equivalent convolutional operators designed to prevent aliasing when evaluating continuous PDE functions.
