image-in-browser/lib/src/formats/webp-encoder.d.ts

Package for encoding / decoding images, transforming images, applying filters, drawing primitives on images on the client side (no need for server Node.js)

/** @format */
import { Encoder, EncoderEncodeOptions } from './encoder.js';
/**
 * Encode an image to the WebP format (lossless).
 *
 * Uses the VP8L lossless bitstream format wrapped in a RIFF/WebP container.
 * Applies the subtract-green transform and LZ77 back-references.
 */
export declare class WebPEncoder implements Encoder {
    /**
     * Lookup table for mapping (x, y) offsets to plane codes for distance encoding.
     * Used in the LZ77 back-reference distance calculation.
     * @private
     */
    private static readonly planeLut;
    /**
     * Indicates whether the encoder supports animation.
     * @private
     */
    private _supportsAnimation;
    /**
     * Gets the value indicating whether the encoder supports animation.
     * @returns {boolean} True if the encoder supports animation, otherwise false.
     */
    get supportsAnimation(): boolean;
    /**
     * Encodes the given image data into the VP8L lossless bitstream.
     * Applies transforms, predictor selection, and entropy coding.
     * @param {MemoryImage} image - The image to encode.
     * @param {number} width - The width of the image.
     * @param {number} height - The height of the image.
     * @returns {Uint8Array} The encoded VP8L bitstream.
     * @private
     */
    private encodeVP8L;
    /**
     * Applies the subtract-green transform to the red and blue channels.
     * This decorrelates color channels for better compression.
     * @param {Uint8Array} r - Red channel data.
     * @param {Uint8Array} g - Green channel data.
     * @param {Uint8Array} b - Blue channel data.
     * @param {number} numPixels - Number of pixels in the image.
     * @private
     */
    private applySubtractGreenTransform;
    /**
     * Selects the best predictor mode for each block in the image.
     * Evaluates candidate predictors and chooses the one with the lowest cost.
     * @param {Uint8Array} r - Red channel data.
     * @param {Uint8Array} g - Green channel data.
     * @param {Uint8Array} b - Blue channel data.
     * @param {number} width - Image width.
     * @param {number} height - Image height.
     * @param {number} blockW - Number of blocks horizontally.
     * @param {number} blockH - Number of blocks vertically.
     * @param {number} blockSize - Size of each block.
     * @returns {number[]} Array of predictor modes for each block.
     * @private
     */
    private selectPredictorModes;
    /**
     * Applies the selected predictor transform to the image channels.
     * Modifies the channel data in-place to store residuals.
     * @param {Uint8Array} r - Red channel data.
     * @param {Uint8Array} g - Green channel data.
     * @param {Uint8Array} b - Blue channel data.
     * @param {Uint8Array} a - Alpha channel data.
     * @param {number} width - Image width.
     * @param {number} height - Image height.
     * @param {number} blockW - Number of blocks horizontally.
     * @param {number} blockSize - Size of each block.
     * @param {number[]} modes - Predictor modes for each block.
     * @private
     */
    private applyPredictorTransform;
    /**
     * Writes the predictor mode subimage to the bitstream.
     * Encodes the predictor modes using Huffman coding.
     * @param {WebPBitWriter} bw - The bit writer.
     * @param {number} blockW - Number of blocks horizontally.
     * @param {number} blockH - Number of blocks vertically.
     * @param {number[]} modes - Predictor modes for each block.
     * @private
     */
    private writePredictorSubImage;
    /**
     * Maps a match length to its corresponding symbol for entropy coding.
     * @param {number} length - The match length.
     * @returns {number} The symbol representing the length.
     * @private
     */
    private lengthSymbol;
    /**
     * Computes the extra bits and value for a given match length symbol.
     * Used for encoding match lengths with additional precision.
     * @param {number} length - The match length.
     * @returns {{ extraBits: number, extraValue: number }} Extra bits and value.
     * @private
     */
    private lengthExtra;
    /**
     * Converts a pixel distance to a plane code for distance entropy coding.
     * Uses a lookup table for small distances and a direct mapping for larger ones.
     * @param {number} width - Image width.
     * @param {number} dist - Pixel distance.
     * @returns {number} The plane code for the distance.
     * @private
     */
    private distToPlaneCode;
    /**
     * Maps a value to its prefix code for distance or length coding.
     * @param {number} v - The value to encode.
     * @returns {number} The prefix code.
     * @private
     */
    private prefixCode;
    /**
     * Computes the extra bits and value for a given prefix code.
     * Used for encoding distances and lengths with additional precision.
     * @param {number} v - The value to encode.
     * @returns {{ extraBits: number, extraValue: number }} Extra bits and value.
     * @private
     */
    private prefixExtra;
    /**
     * Computes the floor of the base-2 logarithm of the given value.
     * @param {number} v - The value to compute the log2 floor for.
     * @returns {number} The floor of log2(v).
     * @private
     */
    private log2Floor;
    /**
     * Builds the Huffman code lengths for the given symbol frequencies.
     * Uses a bounded-length Huffman tree construction.
     * @param {number[]} freq - Symbol frequencies.
     * @param {number} alphabetSize - Number of symbols in the alphabet.
     * @param {number} [maxBits] - Maximum allowed code length.
     * @returns {number[]} Array of code lengths for each symbol.
     * @private
     */
    private buildHuffmanCodeLengths;
    /**
     * Writes the Huffman code tree to the bitstream.
     * Handles special cases for small alphabets and uses RLE for code lengths.
     * @param {WebPBitWriter} bw - The bit writer.
     * @param {number} alphabetSize - Number of symbols in the alphabet.
     * @param {number[]} codeLengths - Huffman code lengths for each symbol.
     * @private
     */
    private writeHuffmanCode;
    /**
     * Builds a run-length encoded (RLE) sequence of code length symbols.
     * Used for compact representation of Huffman code trees.
     * @param {number[]} codeLengths - Huffman code lengths for each symbol.
     * @param {number} alphabetSize - Number of symbols in the alphabet.
     * @returns {WebPClSymbol[]} RLE sequence of code length symbols.
     * @private
     */
    private buildRleSequence;
    /**
     * Generates canonical Huffman codes from code lengths.
     * @param {Int32Array} codeLengths - Huffman code lengths for each symbol.
     * @param {number} numSymbols - Number of symbols in the alphabet.
     * @returns {number[]} Canonical Huffman codes for each symbol.
     * @private
     */
    private canonicalCodes;
    /**
     * Reverses the order of bits in the given value.
     * @param {number} value - The value whose bits to reverse.
     * @param {number} numBits - The number of bits to reverse.
     * @returns {number} The value with bits reversed.
     * @private
     */
    private reverseBits;
    /**
     * Returns a Uint8Array containing the ASCII codes of the given string.
     * @param {string} s - The string to convert.
     * @returns {Uint8Array} The byte array representing the string.
     * @private
     */
    private tag;
    /**
     * Encodes the given image into a WEBP format.
     * @param {EncoderEncodeOptions} opt - The options for encoding.
     * @param {MemoryImage} opt.image - The image to encode.
     * @returns {Uint8Array} The encoded image in WEBP format.
     */
    encode(opt: EncoderEncodeOptions): Uint8Array;
}