jpeg_data_decoder.cc

/*
 * Copyright 2016 Google Inc.
 *
 * 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.
 */

#include "jpeg_data_decoder.h"

#include "output_image.h"

namespace knusperli {

// Mimic libjpeg's heuristics to guess jpeg color space.
// Requires that the jpg has 3 components.
bool HasYCbCrColorSpace(const JPEGData& jpg) {
  bool has_Adobe_marker = false;
  uint8_t Adobe_transform = 0;
  for (const std::string& app : jpg.app_data) {
    if (static_cast<uint8_t>(app[0]) == 0xe0) {
      return true;
    } else if (static_cast<uint8_t>(app[0]) == 0xee && app.size() >= 15) {
      has_Adobe_marker = true;
      Adobe_transform = app[14];
    }
  }
  if (has_Adobe_marker) {
    return (Adobe_transform != 0);
  }
  const int cid0 = jpg.components[0].id;
  const int cid1 = jpg.components[1].id;
  const int cid2 = jpg.components[2].id;
  return (cid0 != 'R' || cid1 != 'G' || cid2 != 'B');
}

std::vector<uint8_t> DecodeJpegToRGB(const JPEGData& jpg) {
  if (jpg.components.size() == 1 ||
      (jpg.components.size() == 3 &&
       HasYCbCrColorSpace(jpg) && (jpg.Is420() || jpg.Is444()))) {
    OutputImage img(jpg.width, jpg.height);
    img.CopyFromJpegData(jpg);
    return img.ToSRGB();
  }
  return std::vector<uint8_t>();
}

}  // namespace knusperli