@ken0106/exif

EXIF APP1 embedded-JPEG thumbnail extractor. Pass the output to @ken0106/core's thumbnailExtractor option to turn full-image decodes into ~5ms thumbnail decodes when the JPEG ships one.

npm install @ken0106/exif

Quick start

import { extractExifThumbnail } from "@ken0106/exif";
import { getPalette } from "@ken0106/core";

const result = await getPalette(jpegUrl, {
  decoders: { jpeg: myJpegDecoder },
  thumbnailExtractor: extractExifThumbnail,
  minThumbnailDimension: 64,  // ignore smaller stubs
});

result.meta.path; // "exif-thumb" when the fast path fired

What it does

Most photos from phones, digital cameras, and professional pipelines carry an embedded JPEG thumbnail inside the EXIF APP1 segment — usually 100–300 pixels wide, under 64KB. When present, decoding that instead of the full image gives you the same palette for a fraction of the cost.

This package is a standalone parser: it walks the JPEG segment list, locates APP1, verifies the "Exif\0\0" identifier, parses the TIFF header, walks IFD0 and IFD1, and returns the bytes at JpegIFOffset of length JpegIFByteCount. No decoder needed — those bytes are themselves a JPEG.

API

extractExifThumbnail(bytes: Uint8Array): {
  bytes: Uint8Array;   // the inner JPEG, starting with 0xFF 0xD8
  offset: number;      // offset into the outer JPEG where it starts
} | undefined;

Returns undefined for PNG/WebP/AVIF, for JPEGs without an EXIF thumbnail, or for malformed EXIF data.

License

MIT