copy EXIF from one JPEG blob to another and return a new JPEG blob.

copyExif.js

// Copyright (c) 2019 Weihang Jian <tonytonyjan@gmail.com>

export default async (src, dest) => {
  const exif = await retrieveExif(src);
  return new Blob([dest.slice(0, 2), exif, dest.slice(2)], {
    type: "image/jpeg"
  });
};

export const SOS = 0xffda,
  APP1 = 0xffe1,
  EXIF = 0x45786966,
  retrieveExif = blob =>
    new Promise((resolve, reject) => {
      const reader = new FileReader();
      reader.addEventListener("load", ({ target: { result: buffer } }) => {
        const view = new DataView(buffer);
        let offset = 0;
        if (view.getUint16(offset) !== 0xffd8)
          return reject("not a valid jpeg");
        offset += 2;

        while (true) {
          const marker = view.getUint16(offset);
          if (marker === SOS) break;
          const size = view.getUint16(offset + 2);
          if (marker === APP1 && view.getUint32(offset + 4) === EXIF)
            return resolve(blob.slice(offset, offset + 2 + size));
          offset += 2 + size;
        }
        return resolve(new Blob());
      });
      reader.readAsArrayBuffer(blob);
    });

copyExifWithoutOrientation.js

// Copyright (c) 2022 Weihang Jian <tonytonyjan@gmail.com>

export default async (srcBlob, destBlob) => {
  const exif = await getApp1Segment(srcBlob);
  return new Blob([destBlob.slice(0, 2), exif, destBlob.slice(2)], {
    type: "image/jpeg",
  });
};

const SOI = 0xffd8,
  SOS = 0xffda,
  APP1 = 0xffe1,
  EXIF = 0x45786966,
  LITTLE_ENDIAN = 0x4949,
  BIG_ENDIAN = 0x4d4d,
  TAG_ID_ORIENTATION = 0x0112,
  TAG_TYPE_SHORT = 3,
  getApp1Segment = (blob) =>
    new Promise((resolve, reject) => {
      const reader = new FileReader();
      reader.addEventListener("load", ({ target: { result: buffer } }) => {
        const view = new DataView(buffer);
        let offset = 0;
        if (view.getUint16(offset) !== SOI) return reject("not a valid JPEG");
        offset += 2;

        while (true) {
          const marker = view.getUint16(offset);
          if (marker === SOS) break;

          const size = view.getUint16(offset + 2);
          if (marker === APP1 && view.getUint32(offset + 4) === EXIF) {
            const tiffOffset = offset + 10;
            let littleEndian;
            switch (view.getUint16(tiffOffset)) {
              case LITTLE_ENDIAN:
                littleEndian = true;
                break;
              case BIG_ENDIAN:
                littleEndian = false;
                break;
              default:
                return reject("TIFF header contains invalid endian");
            }
            if (view.getUint16(tiffOffset + 2, littleEndian) !== 0x2a)
              return reject("TIFF header contains invalid version");

            const ifd0Offset = view.getUint32(tiffOffset + 4, littleEndian);
            let endOfTagsOffset =
              tiffOffset +
              ifd0Offset +
              2 +
              view.getUint16(tiffOffset + ifd0Offset, littleEndian) * 12;
            for (
              let i = tiffOffset + ifd0Offset + 2;
              i < endOfTagsOffset;
              i += 12
            ) {
              const tagId = view.getUint16(i, littleEndian);
              if (tagId == TAG_ID_ORIENTATION) {
                if (view.getUint16(i + 2, littleEndian) !== TAG_TYPE_SHORT)
                  return reject("Orientation data type is invalid");

                if (view.getUint32(i + 4, littleEndian) !== 1)
                  return reject("Orientation data count is invalid");

                view.setUint16(i + 8, 1, littleEndian);
                break;
              }
            }
            return resolve(buffer.slice(offset, offset + 2 + size));
          }
          offset += 2 + size;
        }
        return resolve(new Blob());
      });
      reader.readAsArrayBuffer(blob);
    });

Cool work, is there also a way to copy IPTC, XMP, or simply any kind of metadata from one JPG to another? Best regards.

Thank you for this awesome script.

Many thanks for this gist.
I think there may be a bug on line 59 of copyExifWithoutOrientation: tagId doesn't respect endianness. It should be const tagId = view.getUint16(i, littleEndian);

@basuneko is right, there is a bug

@basuneko thanks for finding this bug! I have updated the gist and it should fix it.

Many thanks! 🍻