Function parseJpegHeader

src/images/jpeg.ts:66–160

(bytes: Uint8Array)

 * @throws {Error} If not a valid JPEG or header is malformed
 */
export function parseJpegHeader(bytes: Uint8Array): JpegInfo {
  if (bytes.length < 2) {
    throw new Error("Invalid JPEG: too short");
  }

  // Check for JPEG magic bytes
  if (bytes[0] !== 0xff || bytes[1] !== MARKER_SOI) {
    throw new Error("Invalid JPEG: missing SOI marker");
  }

  let offset = 2;

  while (offset < bytes.length - 1) {
    // Find next marker
    if (bytes[offset] !== 0xff) {
      throw new Error(`Invalid JPEG: expected marker at offset ${offset}`);
    }

    // Skip padding bytes (0xff 0xff ...)
    while (offset < bytes.length && bytes[offset] === 0xff) {
      offset++;
    }

    if (offset >= bytes.length) {
      throw new Error("Invalid JPEG: unexpected end of file");
    }

    const marker = bytes[offset];
    offset++;

    // Check for SOF marker
    if (isSOFMarker(marker)) {
      if (offset + 7 > bytes.length) {
        throw new Error("Invalid JPEG: SOF segment too short");
      }

      // Skip segment length (2 bytes)
      // const segmentLength = (bytes[offset] << 8) | bytes[offset + 1];

      const bitsPerComponent = bytes[offset + 2];
      const height = (bytes[offset + 3] << 8) | bytes[offset + 4];
      const width = (bytes[offset + 5] << 8) | bytes[offset + 6];
      const numComponents = bytes[offset + 7];

      // Determine color space from number of components
      let colorSpace: "DeviceGray" | "DeviceRGB" | "DeviceCMYK";

      switch (numComponents) {
        case 1:
          colorSpace = "DeviceGray";
          break;
        case 3:
          colorSpace = "DeviceRGB";
          break;
        case 4:
          colorSpace = "DeviceCMYK";
          break;
        default: