pdf.js/src/core/jpeg_stream.js

/* Copyright 2012 Mozilla Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import { createObjectURL, shadow } from '../shared/util';
import { DecodeStream } from './stream';
import { isDict } from './primitives';
import { JpegImage } from './jpg';

/**
 * Depending on the type of JPEG a JpegStream is handled in different ways. For
 * JPEG's that are supported natively such as DeviceGray and DeviceRGB the image
 * data is stored and then loaded by the browser. For unsupported JPEG's we use
 * a library to decode these images and the stream behaves like all the other
 * DecodeStreams.
 */
let JpegStream = (function JpegStreamClosure() {
  function JpegStream(stream, maybeLength, dict, params) {
    // Some images may contain 'junk' before the SOI (start-of-image) marker.
    // Note: this seems to mainly affect inline images.
    let ch;
    while ((ch = stream.getByte()) !== -1) {
      if (ch === 0xFF) { // Find the first byte of the SOI marker (0xFFD8).
        stream.skip(-1); // Reset the stream position to the SOI.
        break;
      }
    }
    this.stream = stream;
    this.maybeLength = maybeLength;
    this.dict = dict;
    this.params = params;

    DecodeStream.call(this, maybeLength);
  }

  JpegStream.prototype = Object.create(DecodeStream.prototype);

  Object.defineProperty(JpegStream.prototype, 'bytes', {
    get: function JpegStream_bytes() {
      // If `this.maybeLength` is null, we'll get the entire stream.
      return shadow(this, 'bytes', this.stream.getBytes(this.maybeLength));
    },
    configurable: true,
  });

  JpegStream.prototype.ensureBuffer = function(requested) {
    // No-op, since `this.readBlock` will always parse the entire image and
    // directly insert all of its data into `this.buffer`.
  };

  JpegStream.prototype.readBlock = function() {
    if (this.eof) {
      return;
    }
    let jpegOptions = {
      decodeTransform: undefined,
      colorTransform: undefined,
    };

    // Checking if values need to be transformed before conversion.
    let decodeArr = this.dict.getArray('Decode', 'D');
    if (this.forceRGB && Array.isArray(decodeArr)) {
      let bitsPerComponent = this.dict.get('BitsPerComponent') || 8;
      let decodeArrLength = decodeArr.length;
      let transform = new Int32Array(decodeArrLength);
      let transformNeeded = false;
      let maxValue = (1 << bitsPerComponent) - 1;
      for (let i = 0; i < decodeArrLength; i += 2) {
        transform[i] = ((decodeArr[i + 1] - decodeArr[i]) * 256) | 0;
        transform[i + 1] = (decodeArr[i] * maxValue) | 0;
        if (transform[i] !== 256 || transform[i + 1] !== 0) {
          transformNeeded = true;
        }
      }
      if (transformNeeded) {
        jpegOptions.decodeTransform = transform;
      }
    }
    // Fetching the 'ColorTransform' entry, if it exists.
    if (isDict(this.params)) {
      let colorTransform = this.params.get('ColorTransform');
      if (Number.isInteger(colorTransform)) {
        jpegOptions.colorTransform = colorTransform;
      }
    }
    const jpegImage = new JpegImage(jpegOptions);

    jpegImage.parse(this.bytes);
    let data = jpegImage.getData({
      width: this.drawWidth,
      height: this.drawHeight,
      forceRGB: this.forceRGB,
      isSourcePDF: true,
    });
    this.buffer = data;
    this.bufferLength = data.length;
    this.eof = true;
  };

  JpegStream.prototype.getIR = function(forceDataSchema = false) {
    return createObjectURL(this.bytes, 'image/jpeg', forceDataSchema);
  };

  return JpegStream;
})();

export {
  JpegStream,
};