/**
 * Apply the inverse color transform: read the residual ARGB image and
 * the per-block coefficients, produce decoded ARGB. Mutates `argb` in
 * place because the caller hands us the post-pixel-decode buffer.
 */
export declare function inverseColorTransform(argb: Uint32Array, width: number, height: number, bits: number, ctImage: Uint32Array, ctWidth: number): void;
/**
 * Forward color transform. Picks per-block coefficients by trying a
 * small grid of `(greenToRed, greenToBlue, redToBlue)` candidates and
 * keeping whichever minimises the sum of absolute residual values
 * across the block. Mutates `argb` in place to hold residuals; returns
 * the coefficient image to be encoded as a sub-image.
 *
 * The candidate grid is chosen to cover the practically-useful range
 * `[-16, 16]` in steps of 8 — narrower than libwebp's exhaustive search
 * but enough to capture the typical greenToRed ≈ 1, greenToBlue ≈ 1.5
 * relationship in natural images. Doubling the grid would buy a few
 * more percent compression at 8× the encode time; we trade it off
 * for speed.
 */
export declare function applyColorTransform(argb: Uint32Array, width: number, height: number, bits: number): { ctImage: Uint32Array, ctWidth: number, ctHeight: number };