SlidingConv: Domain-Specific Description of Sliding Discrete Cosine Transform Convolution for Halide

Abstract

Filtering is a fundamental tool in image processing, and its acceleration affects many applications. Therefore, various algorithmic and hardware accelerations have been proposed for filtering. Recursive processing using infinite impulse response (IIR) filtering is an efficient algorithm, and various hardware acceleration methods have been applied to IIR filtering. In addition, a domain-specific language (DSL) of RecFilter was proposed to generate efficient IIR code for various hardware applications as an extension of image processing language, Halide. Recursive filters based on sliding discrete cosine transform (SDCT) have been the most efficient approximations in recent years. For hardware acceleration, parallelization of recursive filters is challenging. One of the most efficient methods is tile-based parallelization. However, even if a function is optimized and modularized, it is not sufficiently optimized for applications where various pre/post-processing steps are coupled before and after filtering. Additionally, multiplatform deployment requires reimplementation of the code. In this study, we extended Halide for SDCT convolutions to realize efficient computing of image processing applications with filtering, named SlidingConv. The experimental results showed that SlidingConv is faster than the hand-tuned CPU code and 1/1900 of the hand-tuned code length, running more efficiently than de facto libraries like OpenCV. To verify its efficiency, we deployed the code on various hardware (x86/64 CPU with AVX2/AVX-512, ARM CPU, and GPU). In addition, we verified that the proposed method can accelerate image processing with pre/post-processing for filtering. Our code is available at https://fukushimalab.github.io/SlidingConv/.

Keywords

• Image processing
• parallel recursive filtering
• sliding DCT
• domain-specific language
• Halide