/**
 * `@variance-authority/png/difference` — the codec half of known-difference
 * measurement.
 *
 * **Requires a PNG codec**, and that is the only reason it is not in
 * `@variance-authority/raster/difference` with the rest. Decoding is the one step
 * that needs somebody's decoder; the field, the curve, the deltas and the
 * artifact are arithmetic over two arrays and cost nothing, so they live where a
 * caller who already has decoded pixels can reach them without installing this.
 *
 * The split has a practical consequence worth stating: a team whose images arrive
 * as raw RGBA — from a canvas, a WASM renderer, a framebuffer — never installs
 * `pngjs` at all.
 */
import { type DifferenceObservation, type DifferenceMetric, type ImageNormalizationOptions, type NormalizedImage } from '@variance-authority/raster/difference';
/**
 * Decode a PNG into the RGBA the metrics consume.
 *
 * `alphaMode` is reported as `straight` whenever the image carries a non-opaque
 * pixel and `opaque` otherwise, because the distinction changes what a metric
 * does and guessing it wrong is silent. Nothing is resampled, converted or
 * colour-managed: `colorSpace` is declared, not detected, for the same reason the
 * rest of the package refuses to align — a conversion this library performs is a
 * difference this library invented.
 */
export declare function decodeImage(bytes: Buffer, colorSpace?: string): NormalizedImage;
export interface ObservePngDifferenceInput {
    readonly firstImage: Buffer;
    readonly secondImage: Buffer;
    readonly metric: DifferenceMetric;
    readonly severityLevels: readonly number[];
    readonly normalization?: ImageNormalizationOptions;
    /** Declared, never sniffed. Both images must agree. */
    readonly colorSpace?: string;
}
/**
 * Observe the difference between two PNGs.
 *
 * The source hashes are taken over the **encoded** bytes rather than the decoded
 * pixels, because that is what the caller actually has and can look up again.
 */
export declare function observePngDifference(input: ObservePngDifferenceInput): Promise<DifferenceObservation>;
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