PureCV

A high-performance, pure Rust computer vision library focusing on the core and imgproc modules of OpenCV. PureCV is built from the ground up to be memory-safe, thread-safe, and highly portable without the overhead of C++ FFI.

🎯 Philosophy

Unlike existing wrappers, PureCV is a native rewrite. It aims to provide:

• Zero-FFI: No complex linking or C++ toolchain requirements.
• Memory Safety: Elimination of segmentation faults and buffer overflows via Rust's ownership model.
• Modern Parallelism: Native integration with Rayon for effortless multi-core processing.
• Portable SIMD: Optional SIMD acceleration via pulp — auto-detects x86 SSE/AVX, ARM NEON, and WASM simd128 at runtime. Zero unsafe, zero #[cfg(target_arch)].

✨ Features

purecv-core

• Matrix Operations: Multi-dimensional Matrix<T> with support for common arithmetic (add, subtract, multiply, divide) and bitwise logic (bitwise_and, bitwise_or, bitwise_xor, bitwise_not). Matrix and scalar variants for all operations.
• Factory Methods: Intuitive initialization with zeros, ones, eye, and diag.
• Comparison: compare, compare_scalar, min, max, abs_diff, in_range.
• Structural: flip, rotate, transpose, repeat, reshape, hconcat, vconcat, copy_make_border, extract_channel, insert_channel.
• Math: sqrt, exp, log, pow, magnitude, phase, cart_to_polar, polar_to_cart, convert_scale_abs.
• Stats: sum, mean, mean_std_dev, min_max_loc, norm, normalize, count_non_zero, reduce.
• Linear Algebra: gemm, dot, cross, trace, determinant, invert, solve, solve_poly, set_identity.
• Sorting: sort, sort_idx with configurable row/column and ascending/descending flags.
• Clustering: kmeans with random, k-means++, and user-supplied initialization strategies.
• Transforms: transform (per-element matrix transformation), perspective_transform (projective / homography mapping).
• Random Number Generation: randu (uniform distribution), randn (normal/Gaussian distribution), set_rng_seed.
• Channel Management: split, merge, mix_channels.
• Utilities: add_weighted, check_range, absdiff, get_tick_count, get_tick_frequency.
• ndarray Interop: Optional, zero-cost conversions to/from ndarray::Array3 via the ndarray feature flag.
• SIMD Acceleration (simd feature): Trait-based dispatch via pulp for f32, f64, and u8 types. Accelerated operations include add, sub, mul, div, min, max, sqrt, dot, sum, add_weighted, convert_scale_abs, and magnitude. Falls back to scalar loops at zero cost when disabled.

purecv-imgproc

• Color Conversions: High-performance cvt_color supporting RGB, BGR, Gray, RGBA, BGRA and more. Up to 6.6× speedup with Parallel + SIMD. SIMD-accelerated paths (simd feature) use fixed-point integer arithmetic (coefficients 77/150/29 ≈ 0.299/0.587/0.114 × 256) for all *_to_gray conversions — portable to x86 SSE/AVX, ARM NEON, and WASM simd128 via pulp.
• Edge Detection: canny, sobel, scharr, laplacian. Optimized fast_deriv_3x3 kernel delivers up to 12× speedup with Parallel. For f32 inputs, the pulp-powered simd_deriv_3x3_row_f32 interior kernel adds a further 1.5× boost, reaching 22× total speedup (28.59 ms → 1.28 ms) with Parallel + SIMD — the highest combined speedup in the project.
• Filtering: blur, box_filter, gaussian_blur, median_blur, bilateral_filter. The bilateral filter achieves 7.1× speedup with Parallel (1.43 s → 202 ms on 512×512); SIMD provides no additional gain due to the non-vectorizable per-pixel exponential weight computation.
• Thresholding: threshold with all 5 OpenCV-compatible types (BINARY, BINARY_INV, TRUNC, TOZERO, TOZERO_INV). SIMD-accelerated fast path for u8, f32, and f64 via the SimdElement::simd_threshold() trait method. Works seamlessly with parallel feature for row-level Rayon dispatch.

🚀 Getting Started

Installation

Add the following to your Cargo.toml:

[dependencies]
purecv = "0.1"

Feature Flags

Flag	Default	Description
std	✅	Standard library support
parallel	✅	Multi-core parallelism via Rayon
ndarray	❌	Interop with the ndarray crate (zero-cost views & ownership transfers)
simd	❌	SIMD acceleration via pulp (x86 SSE/AVX, ARM NEON, WASM simd128)
wasm	❌	WebAssembly-specific optimizations

To enable the ndarray feature:

[dependencies]
purecv = { version = "0.1", features = ["ndarray"] }

To enable SIMD + Parallel for maximum performance:

[dependencies]
purecv = { version = "0.1", features = ["parallel", "simd"] }

Usage Example

use purecv::core::{Matrix, Size, Scalar};
use purecv::imgproc::{cvt_color, ColorConversionCodes};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Create a 3-channel matrix initialized to ones
    let mat = Matrix::<f32>::ones(480, 640, 3);
    
    // Create an identity matrix
    let identity = Matrix::<f32>::eye(3, 3, 1);
    
    println!("Matrix size: {}x{}", mat.cols, mat.rows);
    Ok(())
}

ndarray Interoperability

With the ndarray feature enabled, you can convert between Matrix<T> and ndarray::Array3<T>:

use purecv::core::Matrix;

// Matrix → ndarray (zero-cost view)
let mat = Matrix::<f32>::ones(480, 640, 3);
let view = mat.as_ndarray_view(); // ArrayView3<f32>, shape (480, 640, 3)

// Matrix → ndarray (ownership transfer)
let mat2 = Matrix::<f32>::ones(480, 640, 3);
let arr = mat2.into_ndarray();

// ndarray → Matrix (guarantees contiguous C-order layout for SIMD/WASM)
let mat3 = Matrix::from_ndarray(arr);

// Also works via the From trait
let arr2 = ndarray::Array3::<f32>::zeros((100, 100, 3));
let mat4: Matrix<f32> = Matrix::from(arr2);

Running Examples

Explore the capabilities of PureCV by running the provided examples:

# Basic matrix arithmetic
cargo run --example arithmetic

# Structural operations (flip, rotate, split/merge)
cargo run --example structural_ops

# Color conversion (RGB to Grayscale)
cargo run --example color_conversion

# Thresholding — all 5 types (BINARY, BINARY_INV, TRUNC, TOZERO, TOZERO_INV)
cargo run --example threshold

# Image filters (blur, gaussian, canny, sobel, …) — requires examples/data/butterfly.jpg
cargo run --example filters

🧪 Testing & Benchmarking

Running Tests

PureCV uses a comprehensive suite of unit tests to ensure correctness and parity with OpenCV.

# Run all tests
cargo test

Running Benchmarks

Performance is a core focus. Benchmarks are available for arithm, imgproc, and structural modules across four configurations:

# Standard (sequential, no SIMD)
cargo bench --no-default-features

# SIMD Only (sequential + auto-vectorization)
RUSTFLAGS="-C target-cpu=native" cargo bench --no-default-features

# Parallel (Rayon multi-threading)
cargo bench --features parallel

# Parallel + SIMD (maximum throughput)
RUSTFLAGS="-C target-cpu=native" cargo bench --features parallel

Key Performance Highlights (1024×1024 matrices, updated 2026-03-17)

Operation	Standard	Parallel + SIMD	Speedup
cvt_color_rgb2gray	2.66 ms	404 µs	6.6×
sobel_3x3 (generic)	22.79 ms	1.87 ms	12×
sobel_3x3_f32_dx ★	28.59 ms	1.28 ms	22×
sobel_3x3_f32_dy ★	26.24 ms	1.27 ms	21×
bilateral_filter (512×512)	1.43 s	202 ms	7.1×
laplacian_3x3	45.91 ms	4.44 ms	10.4×
dot	997 µs	157 µs	6.4×
gemm_256×256	15.71 ms	4.40 ms	3.7×
canny	57.61 ms	12.54 ms	4.6×

★ Uses non-zero sinusoidal data to exercise the simd_deriv_3x3_row_f32 SIMD kernel. Best combined speedup in the project.

Full results in benches/benchmark_results.md

🗺 Roadmap

• Phase 1: Core Foundation - Matrix types, arithmetic, geometric utilities, and basic structural transforms.
• Phase 2: Performance - SIMD acceleration via pulp, Rayon parallelism, and Criterion benchmarking across 32 operations.
  • PR 1 — SIMD infra + arithm kernels (add, sub, mul, div, dot, magnitude, add_weighted, convert_scale_abs, sqrt, min, max, sum).
  • PR 2 — Color + Threshold SIMD: fixed-point cvt_color_*_to_gray kernels, simd_threshold() for all 5 types on u8/f32/f64, new threshold example.
  • PR 3 — Derivatives SIMD: fast_deriv_3x3 interior SIMD pass (simd_deriv_3x3_row_f32) achieving 22× speedup on sobel_3x3_f32; new benchmarks for sobel_3x3_f32_dx/dy and bilateral_filter.
• Phase 3: WebAssembly - wasm-bindgen wrappers, wasm-pack build, CI matrix with wasm32-unknown-unknown + simd128.
• Phase 4: Image Processing - Advanced filtering, convolutions, and feature detection.
• Visual examples — Load real images, apply threshold + cvt_color, save PNG output (follow-up to filters.rs).

📄 License

This project is licensed under the LGPL-3.0 License.