/**
 * CCITT Fax Group 3/Group 4 decoder that reads bits from a byte source and
 * reconstructs monochrome scanlines using 1D/2D coding, EOL/RTC handling, and
 * optional byte alignment and black/white polarity.
 *
 * @private
 */
export declare class _PdfFaxDecoder {
    private _source;
    private _eof;
    private _encoding;
    private _endOfLine;
    private _byteAlign;
    private _columns;
    private _rows;
    private _endOfBlock;
    private _black;
    private _codingLine;
    private _referenceLine;
    private _codingPosition;
    private _row;
    private _nextLine;
    private _inputBits;
    private _inputBuffer;
    private _outputBits;
    _text: string;
    private _rowsDone;
    err: boolean;
    constructor(source: {
        next: Function;
    }, options?: any);
    readNextChar(): number;
    private _addPixels;
    private _addPixelsNeg;
    private _findTableCode;
    private _getTwoDimCode;
    private _getWhiteCode;
    private _getBlackCode;
    /**
     * Peeks the next `n` bits from the input buffer; pads with zeros
     * if input is partially exhausted.
     *
     * @private
     * @param {number} n The number of bits to look ahead (≤ 16).
     * @returns {number} The unsigned value of the next `n` bits, or `-1` if no more input is available.
     */
    _lookBits(n: number): number;
    /**
     * Consumes `n` bits from the input buffer safely clamps to zero when underflowing.
     *
     * @private
     * @param {number} n The number of bits to discard.
     * @returns {void}
     */
    _eatBits(n: number): void;
}