export type SignatureBackgroundRemovalOptions = {
    /** Minimum RGB channel value treated as background white (0–255). */
    threshold?: number;
    /** Feather edge between background and ink (0–255). */
    softness?: number;
};
/** Turn near-white pixels transparent so signatures overlay documents cleanly. */
export declare function makeSignatureTransparent(dataUrl: string, options?: SignatureBackgroundRemovalOptions): Promise<string>;
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