/** @format */
/**
 * Provides filter and unfilter operations for WebP images.
 */
export declare class WebPFilters {
    /** No filter constant. */
    static readonly filterNone = 0;
    /** Horizontal filter constant. */
    static readonly filterHorizontal = 1;
    /** Vertical filter constant. */
    static readonly filterVertical = 2;
    /** Gradient filter constant. */
    static readonly filterGradient = 3;
    /** End marker for filters. */
    static readonly filterLast: number;
    /** Best filter constant. */
    static readonly filterBest = 5;
    /** Fast filter constant. */
    static readonly filterFast = 6;
    /** Array of unfilter functions. */
    static readonly unfilters: (typeof WebPFilters.horizontalUnfilter | undefined)[];
    /**
     * Predicts a line of pixels using previous data.
     */
    private static predictLine;
    /**
     * Applies horizontal filter or unfilter to image data.
     */
    private static doHorizontalFilter;
    /**
     * Applies vertical filter or unfilter to image data.
     */
    private static doVerticalFilter;
    /**
     * Predicts a gradient value for filtering.
     */
    private static gradientPredictor;
    /**
     * Applies gradient filter or unfilter to image data.
     */
    private static doGradientFilter;
    /**
     * Applies horizontal filter to image data.
     */
    private static horizontalFilter;
    /**
     * Applies horizontal unfilter to image data.
     */
    private static horizontalUnfilter;
    /**
     * Applies vertical filter to image data.
     */
    private static verticalFilter;
    /**
     * Applies vertical unfilter to image data.
     */
    private static verticalUnfilter;
    /**
     * Applies gradient filter to image data.
     */
    private static gradientFilter;
    /**
     * Applies gradient unfilter to image data.
     */
    private static gradientUnfilter;
}