/**
 * GaussianSmoother — 3D Gaussian smoothing for segmentation masks.
 *
 * Applies a separable 3D Gaussian blur to a single label channel within a
 * MaskVolume, then thresholds the result back to a binary mask. This smooths
 * jagged edges and fills small holes in segmentation annotations.
 *
 * Pure, stateless utility — no DOM/Canvas/GUI dependencies.
 *
 * Performance: uses direct typed-array access (bypassing getVoxel/setVoxel
 * boundary checks) and branch-free convolution for the interior region.
 */
import type { MaskVolume } from './MaskVolume';
export declare class GaussianSmoother {
    /**
     * Smooth a single label channel in-place using separable 3D Gaussian blur.
     *
     * Steps:
     *  1. Extract — create a Float32Array with 1.0 where voxel === channel, 0.0 elsewhere.
     *  2. Blur — apply separable Gaussian (X → Y → Z) on the float buffer.
     *  3. Threshold — binarize at 0.5.
     *  4. Write back — overwrite/erase voxels according to the thresholded result.
     *
     * @param volume  The MaskVolume to operate on (modified in-place).
     * @param channel The label value to smooth (must be > 0).
     * @param sigma   Base Gaussian sigma in voxel units (default 1.0).
     * @param spacing Optional voxel spacing [sx, sy, sz]. When provided, per-axis
     *                sigma is computed as `sigma / spacing[axis]` so that the
     *                physical smoothing radius is isotropic.
     */
    static gaussianSmooth3D(volume: MaskVolume, channel: number, sigma?: number, spacing?: [number, number, number]): void;
    /**
     * Generate a normalized 1D Gaussian kernel truncated at ±3σ.
     *
     * @param sigma Standard deviation (in voxels). Must be > 0.
     * @returns Normalized Float32Array of odd length.
     */
    static generateKernel1D(sigma: number): Float32Array;
    /**
     * In-place single-axis convolution with zero-padding at boundaries.
     *
     * Uses a 3-segment approach: left boundary (with bounds check),
     * middle interior (branch-free, ~95% of work), right boundary
     * (with bounds check). This eliminates per-element branching
     * in the hot inner loop.
     *
     * @param data   Flat float buffer (width × height × depth).
     * @param width  X dimension.
     * @param height Y dimension.
     * @param depth  Z dimension.
     * @param axis   0 = X, 1 = Y, 2 = Z.
     * @param kernel 1D convolution kernel (odd length).
     */
    private static convolve1D;
}