diff --git a/src/image.cc b/src/image.cc
index 5ebffc1..3d4eef8 100644
--- a/src/image.cc
+++ b/src/image.cc
@@ -211,457 +211,6 @@ bool Image::SaveAsPPM(const char *filename, bool overwrite, bool packed) {
   return SaveAsPPM(std::string(filename), overwrite, packed);
 }
 
-void Image::DecodePNG(const std::string &filename) {
-  FILE *file = std::fopen(filename.c_str(), "rb");
-
-  // Check header of file to check if it is actually a png file.
-  {
-    std::array<unsigned char, 8> buf;
-    if (std::fread(buf.data(), 1, 8, file) != 8) {
-      std::fclose(file);
-      std::cout << "ERROR: File \"" << filename << "\" is smaller than 8 bytes"
-                << std::endl;
-      return;
-    } else if (png_sig_cmp(reinterpret_cast<png_const_bytep>(buf.data()), 0,
-                           8) != 0) {
-      // not png file, do nothing
-      std::fclose(file);
-      std::cout << "ERROR: File \"" << filename << "\" is not a png file"
-                << std::endl;
-      return;
-    }
-  }
-
-  // seek to head of file
-  std::rewind(file);
-
-  // init required structs for png decoding
-  png_structp png_ptr =
-      png_create_read_struct(PNG_LIBPNG_VER_STRING, nullptr, nullptr, nullptr);
-  if (!png_ptr) {
-    std::cout << "ERROR: Failed to initialize libpng (png_ptr) for decoding "
-                 "PNG file \""
-              << filename << '"' << std::endl;
-    std::fclose(file);
-    return;
-  }
-
-  png_infop png_info_ptr = png_create_info_struct(png_ptr);
-  if (!png_info_ptr) {
-    std::cout << "ERROR: Failed to initialize libpng (png_infop) for decoding "
-                 "PNG file \""
-              << filename << '"' << std::endl;
-    png_destroy_read_struct(&png_ptr, nullptr, nullptr);
-    std::fclose(file);
-    return;
-  }
-
-  png_infop png_end_info_ptr = png_create_info_struct(png_ptr);
-  if (!png_end_info_ptr) {
-    std::cout << "ERROR: Failed to initialize libpng (end png_infop) for "
-                 "decoding PNG file \""
-              << filename << '"' << std::endl;
-    png_destroy_read_struct(&png_ptr, &png_info_ptr, nullptr);
-    std::fclose(file);
-    return;
-  }
-
-  // required to handle libpng errors
-  if (setjmp(png_jmpbuf(png_ptr))) {
-    png_destroy_read_struct(&png_ptr, &png_info_ptr, &png_end_info_ptr);
-    std::fclose(file);
-    return;
-  }
-
-  // pass the FILE pointer to libpng
-  png_init_io(png_ptr, file);
-
-  // have libpng process the png data
-  png_read_png(png_ptr, png_info_ptr, PNG_TRANSFORM_IDENTITY, nullptr);
-
-  // get image width (in pixels)
-  width_ = png_get_image_width(png_ptr, png_info_ptr);
-
-  // get image height (in pixels)
-  height_ = png_get_image_height(png_ptr, png_info_ptr);
-
-  // get channel count of image
-  unsigned int channels = png_get_channels(png_ptr, png_info_ptr);
-  if (channels == 1) {
-    is_grayscale_ = true;
-  } else {
-    is_grayscale_ = false;
-  }
-
-  if (height_ > PNG_UINT_32_MAX) {
-    png_error(png_ptr, "Image is too tall to process in memory");
-  } else if (width_ > PNG_UINT_32_MAX) {
-    png_error(png_ptr, "Image is too wide to process in memory");
-  }
-
-  png_byte **row_pointers = png_get_rows(png_ptr, png_info_ptr);
-
-  data_.clear();
-  if (channels == 3 || channels == 4) {
-    data_.reserve(width_ * 4 * height_);
-  } else if (channels == 1) {
-    data_.reserve(width_ * height_);
-  } else {
-    std::cout << "ERROR: PNG has invalid channel count == " << channels
-              << std::endl;
-    png_destroy_read_struct(&png_ptr, &png_info_ptr, &png_end_info_ptr);
-    return;
-  }
-  for (unsigned int y = 0; y < height_; ++y) {
-    for (unsigned int x = 0; x < width_; ++x) {
-      if (is_grayscale_) {
-        data_.push_back(row_pointers[y][x]);
-      } else if (channels == 3) {
-        for (unsigned int c = 0; c < channels; ++c) {
-          data_.push_back(row_pointers[y][x * channels + c]);
-        }
-        data_.push_back(255);
-      } else /* if (channels == 4) */ {
-        for (unsigned int c = 0; c < channels; ++c) {
-          data_.push_back(row_pointers[y][x * channels + c]);
-        }
-      }
-    }
-  }
-
-  // cleanup
-  png_destroy_read_struct(&png_ptr, &png_info_ptr, &png_end_info_ptr);
-  fclose(file);
-
-  // verify
-  if (is_grayscale_) {
-    if (data_.size() != width_ * height_) {
-      std::cout << "WARNING: data_.size() doesn't match width_ * height_"
-                << std::endl;
-    }
-  } else {
-    if (data_.size() != 4 * width_ * height_) {
-      std::cout << "WARNING: data_.size() doesn't match 4 * width_ * height_"
-                << std::endl;
-    }
-  }
-}
-
-void Image::DecodePGM(const std::string &filename) {
-  is_grayscale_ = true;
-
-  std::ifstream ifs(filename);
-  if (!ifs.is_open()) {
-    std::cout << "ERROR: Failed to open file \"" << filename << '"'
-              << std::endl;
-    return;
-  }
-
-  std::string str_input;
-  int int_input;
-  ifs >> str_input;
-  if (!ifs.good()) {
-    std::cout << "ERROR: Failed to parse file (PGM first identifier) \""
-              << filename << '"' << std::endl;
-    return;
-  }
-
-  if (str_input.compare("P2") == 0) {
-    // data stored in ascii format
-
-    // get width
-    ifs >> int_input;
-    if (!ifs.good() || int_input <= 0) {
-      std::cout << "ERROR: Failed to parse file (PGM width) \"" << filename
-                << '"' << std::endl;
-      return;
-    }
-    width_ = int_input;
-
-    // get height
-    ifs >> int_input;
-    if (!ifs.good() || int_input <= 0) {
-      std::cout << "ERROR: Failed to parse file (PGM height) \"" << filename
-                << '"' << std::endl;
-      return;
-    }
-    height_ = int_input;
-
-    // get max_value
-    ifs >> int_input;
-    if (!ifs.good() || int_input <= 0) {
-      std::cout << "ERROR: Failed to parse file (PGM max) \"" << filename << '"'
-                << std::endl;
-      return;
-    }
-    float max_value = int_input;
-
-    // parse data
-    data_.clear();
-    data_.reserve(width_ * height_);
-    float value;
-    for (unsigned int i = 0; i < width_ * height_; ++i) {
-      ifs >> int_input;
-      if (!ifs.good()) {
-        std::cout << "ERROR: Failed to parse file (PGM data) \"" << filename
-                  << '"' << std::endl;
-        return;
-      }
-      value = static_cast<float>(int_input) / max_value;
-      data_.push_back(std::round(value * 255.0F));
-    }
-  } else if (str_input.compare("P5") == 0) {
-    // data stored in raw format
-
-    // get width
-    ifs >> int_input;
-    if (!ifs.good() || int_input <= 0) {
-      std::cout << "ERROR: Failed to parse file (PGM width) \"" << filename
-                << '"' << std::endl;
-      return;
-    }
-    width_ = int_input;
-
-    // get height
-    ifs >> int_input;
-    if (!ifs.good() || int_input <= 0) {
-      std::cout << "ERROR: Failed to parse file (PGM height) \"" << filename
-                << '"' << std::endl;
-      return;
-    }
-    height_ = int_input;
-
-    // get max_value
-    ifs >> int_input;
-    if (!ifs.good() || int_input <= 0) {
-      std::cout << "ERROR: Failed to parse file (PGM max) \"" << filename << '"'
-                << std::endl;
-      return;
-    }
-    int max_value_int = int_input;
-    float max_value = int_input;
-
-    // validate max_value
-    if (max_value_int != 255 && max_value_int != 65535) {
-      std::cout << "ERROR: Invalid max value for PGM (should be 255 or 65535) "
-                   "(filename \""
-                << filename << "\")" << std::endl;
-      return;
-    }
-
-    // extract whitespace before data
-    {
-      int c = ifs.get();
-      if (c != '\n' && c != ' ') {
-        std::cout << "WARNING: File data after PGM max is not whitespace "
-                     "(filename \""
-                  << filename << "\")"
-                  << " value is " << c << std::endl;
-      }
-
-      if (!ifs.good()) {
-        std::cout << "ERROR: Failed to parse file (PGM after whitespace) \""
-                  << filename << '"' << std::endl;
-        return;
-      }
-    }
-
-    // parse raw data
-    data_.clear();
-    data_.reserve(width_ * height_);
-    float value;
-    for (unsigned int i = 0; i < width_ * height_; ++i) {
-      if (max_value_int == 255) {
-        value = ifs.get() / max_value;
-        data_.push_back(std::round(value * 255.0F));
-        if (!ifs.good()) {
-          std::cout << "ERROR: Failed to parse file (PGM data) \"" << filename
-                    << '"' << std::endl;
-          return;
-        }
-      } else /* if (max_value_int == 65535) */ {
-        value = (ifs.get() & 0xFF) | ((ifs.get() << 8) & 0xFF00);
-        value /= max_value;
-        data_.push_back(std::round(value * 255.0F));
-        if (!ifs.good()) {
-          std::cout << "ERROR: Failed to parse file (PGM data 16-bit) \""
-                    << filename << '"' << std::endl;
-          return;
-        }
-      }
-    }
-
-    if (ifs.get() != decltype(ifs)::traits_type::eof()) {
-      std::cout << "WARNING: Trailing data in PGM file \"" << filename << '"'
-                << std::endl;
-    }
-  } else {
-    std::cout << "ERROR: Invalid \"magic number\" in header of file \""
-              << filename << '"' << std::endl;
-  }
-}
-
-void Image::DecodePPM(const std::string &filename) {
-  is_grayscale_ = false;
-  std::ifstream ifs(filename);
-  if (!ifs.is_open()) {
-    std::cout << "ERROR: Failed to open file \"" << filename << '"'
-              << std::endl;
-    return;
-  }
-
-  std::string str_input;
-  int int_input;
-  ifs >> str_input;
-  if (!ifs.good()) {
-    std::cout << "ERROR: Failed to parse file (PPM first identifier) \""
-              << filename << '"' << std::endl;
-    return;
-  }
-
-  if (str_input.compare("P3") == 0) {
-    // data stored in ascii format
-
-    // get width
-    ifs >> int_input;
-    if (!ifs.good() || int_input <= 0) {
-      std::cout << "ERROR: Failed to parse file (PPM width) \"" << filename
-                << '"' << std::endl;
-      return;
-    }
-    width_ = int_input;
-
-    // get height
-    ifs >> int_input;
-    if (!ifs.good() || int_input <= 0) {
-      std::cout << "ERROR: Failed to parse file (PPM height) \"" << filename
-                << '"' << std::endl;
-      return;
-    }
-    height_ = int_input;
-
-    // get max_value
-    ifs >> int_input;
-    if (!ifs.good() || int_input <= 0) {
-      std::cout << "ERROR: Failed to parse file (PPM max) \"" << filename << '"'
-                << std::endl;
-      return;
-    }
-    float max_value = int_input;
-
-    // parse data
-    data_.clear();
-    data_.reserve(width_ * height_ * 4);
-    float value;
-    for (unsigned int i = 0; i < width_ * height_ * 3; ++i) {
-      ifs >> int_input;
-      if (!ifs.good()) {
-        std::cout << "ERROR: Failed to parse file (PPM data) \"" << filename
-                  << '"' << std::endl;
-        return;
-      }
-      value = static_cast<float>(int_input) / max_value;
-      data_.push_back(std::round(value * 255.0F));
-      if (i % 3 == 2) {
-        // PPM is RGB but Image stores as RGBA
-        data_.push_back(255);
-      }
-    }
-  } else if (str_input.compare("P6") == 0) {
-    // data stored in raw format
-
-    // get width
-    ifs >> int_input;
-    if (!ifs.good() || int_input <= 0) {
-      std::cout << "ERROR: Failed to parse file (PPM width) \"" << filename
-                << '"' << std::endl;
-      return;
-    }
-    width_ = int_input;
-
-    // get height
-    ifs >> int_input;
-    if (!ifs.good() || int_input <= 0) {
-      std::cout << "ERROR: Failed to parse file (PPM height) \"" << filename
-                << '"' << std::endl;
-      return;
-    }
-    height_ = int_input;
-
-    // get max_value
-    ifs >> int_input;
-    if (!ifs.good() || int_input <= 0) {
-      std::cout << "ERROR: Failed to parse file (PPM max) \"" << filename << '"'
-                << std::endl;
-      return;
-    }
-    int max_value_int = int_input;
-    float max_value = int_input;
-
-    // validate max_value
-    if (max_value_int != 255 && max_value_int != 65535) {
-      std::cout << "ERROR: Invalid max value for PPM (should be 255 or 65535) "
-                   "(filename \""
-                << filename << "\")" << std::endl;
-      return;
-    }
-
-    // extract whitespace before data
-    {
-      int c = ifs.get();
-      if (c != '\n' && c != ' ') {
-        std::cout
-            << "WARNING: File data after PPM max is not whitespace (filename \""
-            << filename << "\") value is " << c << std::endl;
-      }
-
-      if (!ifs.good()) {
-        std::cout << "ERROR: Failed to parse file (PPM after whitespace) \""
-                  << filename << '"' << std::endl;
-        return;
-      }
-    }
-
-    // parse raw data
-    data_.clear();
-    data_.reserve(width_ * height_ * 4);
-    float value;
-    for (unsigned int i = 0; i < width_ * height_ * 3; ++i) {
-      if (max_value_int == 255) {
-        value = ifs.get() / max_value;
-        data_.push_back(std::round(value * 255.0F));
-        if (!ifs.good()) {
-          std::cout << "ERROR: Failed to parse file (PPM data) \"" << filename
-                    << '"' << std::endl;
-          return;
-        }
-      } else /* if (max_value_int == 65535) */ {
-        value = (ifs.get() & 0xFF) | ((ifs.get() << 8) & 0xFF00);
-        value /= max_value;
-        data_.push_back(std::round(value * 255.0F));
-        if (!ifs.good()) {
-          std::cout << "ERROR: Failed to parse file (PPM data 16-bit) \""
-                    << filename << '"' << std::endl;
-          return;
-        }
-      }
-
-      if (i % 3 == 2) {
-        // PPM is RGB but Image stores as RGBA
-        data_.push_back(255);
-      }
-    }
-
-    if (ifs.get() != decltype(ifs)::traits_type::eof()) {
-      std::cout << "WARNING: Trailing data in PPM file \"" << filename << '"'
-                << std::endl;
-    }
-  } else {
-    std::cout << "ERROR: Invalid \"magic number\" in header of file \""
-              << filename << '"' << std::endl;
-  }
-}
-
 uint8_t Image::ColorToGray(uint8_t red, uint8_t green, uint8_t blue) {
   // values taken from Wikipedia article about conversion of color to grayscale
   double y_linear = 0.2126 * (red / 255.0) + 0.7152 * (green / 255.0) +
@@ -1152,3 +701,454 @@ OpenCLHandle::Ptr Image::GetOpenCLHandle() {
 
   return opencl_handle_;
 }
+
+void Image::DecodePNG(const std::string &filename) {
+  FILE *file = std::fopen(filename.c_str(), "rb");
+
+  // Check header of file to check if it is actually a png file.
+  {
+    std::array<unsigned char, 8> buf;
+    if (std::fread(buf.data(), 1, 8, file) != 8) {
+      std::fclose(file);
+      std::cout << "ERROR: File \"" << filename << "\" is smaller than 8 bytes"
+                << std::endl;
+      return;
+    } else if (png_sig_cmp(reinterpret_cast<png_const_bytep>(buf.data()), 0,
+                           8) != 0) {
+      // not png file, do nothing
+      std::fclose(file);
+      std::cout << "ERROR: File \"" << filename << "\" is not a png file"
+                << std::endl;
+      return;
+    }
+  }
+
+  // seek to head of file
+  std::rewind(file);
+
+  // init required structs for png decoding
+  png_structp png_ptr =
+      png_create_read_struct(PNG_LIBPNG_VER_STRING, nullptr, nullptr, nullptr);
+  if (!png_ptr) {
+    std::cout << "ERROR: Failed to initialize libpng (png_ptr) for decoding "
+                 "PNG file \""
+              << filename << '"' << std::endl;
+    std::fclose(file);
+    return;
+  }
+
+  png_infop png_info_ptr = png_create_info_struct(png_ptr);
+  if (!png_info_ptr) {
+    std::cout << "ERROR: Failed to initialize libpng (png_infop) for decoding "
+                 "PNG file \""
+              << filename << '"' << std::endl;
+    png_destroy_read_struct(&png_ptr, nullptr, nullptr);
+    std::fclose(file);
+    return;
+  }
+
+  png_infop png_end_info_ptr = png_create_info_struct(png_ptr);
+  if (!png_end_info_ptr) {
+    std::cout << "ERROR: Failed to initialize libpng (end png_infop) for "
+                 "decoding PNG file \""
+              << filename << '"' << std::endl;
+    png_destroy_read_struct(&png_ptr, &png_info_ptr, nullptr);
+    std::fclose(file);
+    return;
+  }
+
+  // required to handle libpng errors
+  if (setjmp(png_jmpbuf(png_ptr))) {
+    png_destroy_read_struct(&png_ptr, &png_info_ptr, &png_end_info_ptr);
+    std::fclose(file);
+    return;
+  }
+
+  // pass the FILE pointer to libpng
+  png_init_io(png_ptr, file);
+
+  // have libpng process the png data
+  png_read_png(png_ptr, png_info_ptr, PNG_TRANSFORM_IDENTITY, nullptr);
+
+  // get image width (in pixels)
+  width_ = png_get_image_width(png_ptr, png_info_ptr);
+
+  // get image height (in pixels)
+  height_ = png_get_image_height(png_ptr, png_info_ptr);
+
+  // get channel count of image
+  unsigned int channels = png_get_channels(png_ptr, png_info_ptr);
+  if (channels == 1) {
+    is_grayscale_ = true;
+  } else {
+    is_grayscale_ = false;
+  }
+
+  if (height_ > PNG_UINT_32_MAX) {
+    png_error(png_ptr, "Image is too tall to process in memory");
+  } else if (width_ > PNG_UINT_32_MAX) {
+    png_error(png_ptr, "Image is too wide to process in memory");
+  }
+
+  png_byte **row_pointers = png_get_rows(png_ptr, png_info_ptr);
+
+  data_.clear();
+  if (channels == 3 || channels == 4) {
+    data_.reserve(width_ * 4 * height_);
+  } else if (channels == 1) {
+    data_.reserve(width_ * height_);
+  } else {
+    std::cout << "ERROR: PNG has invalid channel count == " << channels
+              << std::endl;
+    png_destroy_read_struct(&png_ptr, &png_info_ptr, &png_end_info_ptr);
+    return;
+  }
+  for (unsigned int y = 0; y < height_; ++y) {
+    for (unsigned int x = 0; x < width_; ++x) {
+      if (is_grayscale_) {
+        data_.push_back(row_pointers[y][x]);
+      } else if (channels == 3) {
+        for (unsigned int c = 0; c < channels; ++c) {
+          data_.push_back(row_pointers[y][x * channels + c]);
+        }
+        data_.push_back(255);
+      } else /* if (channels == 4) */ {
+        for (unsigned int c = 0; c < channels; ++c) {
+          data_.push_back(row_pointers[y][x * channels + c]);
+        }
+      }
+    }
+  }
+
+  // cleanup
+  png_destroy_read_struct(&png_ptr, &png_info_ptr, &png_end_info_ptr);
+  fclose(file);
+
+  // verify
+  if (is_grayscale_) {
+    if (data_.size() != width_ * height_) {
+      std::cout << "WARNING: data_.size() doesn't match width_ * height_"
+                << std::endl;
+    }
+  } else {
+    if (data_.size() != 4 * width_ * height_) {
+      std::cout << "WARNING: data_.size() doesn't match 4 * width_ * height_"
+                << std::endl;
+    }
+  }
+}
+
+void Image::DecodePGM(const std::string &filename) {
+  is_grayscale_ = true;
+
+  std::ifstream ifs(filename);
+  if (!ifs.is_open()) {
+    std::cout << "ERROR: Failed to open file \"" << filename << '"'
+              << std::endl;
+    return;
+  }
+
+  std::string str_input;
+  int int_input;
+  ifs >> str_input;
+  if (!ifs.good()) {
+    std::cout << "ERROR: Failed to parse file (PGM first identifier) \""
+              << filename << '"' << std::endl;
+    return;
+  }
+
+  if (str_input.compare("P2") == 0) {
+    // data stored in ascii format
+
+    // get width
+    ifs >> int_input;
+    if (!ifs.good() || int_input <= 0) {
+      std::cout << "ERROR: Failed to parse file (PGM width) \"" << filename
+                << '"' << std::endl;
+      return;
+    }
+    width_ = int_input;
+
+    // get height
+    ifs >> int_input;
+    if (!ifs.good() || int_input <= 0) {
+      std::cout << "ERROR: Failed to parse file (PGM height) \"" << filename
+                << '"' << std::endl;
+      return;
+    }
+    height_ = int_input;
+
+    // get max_value
+    ifs >> int_input;
+    if (!ifs.good() || int_input <= 0) {
+      std::cout << "ERROR: Failed to parse file (PGM max) \"" << filename << '"'
+                << std::endl;
+      return;
+    }
+    float max_value = int_input;
+
+    // parse data
+    data_.clear();
+    data_.reserve(width_ * height_);
+    float value;
+    for (unsigned int i = 0; i < width_ * height_; ++i) {
+      ifs >> int_input;
+      if (!ifs.good()) {
+        std::cout << "ERROR: Failed to parse file (PGM data) \"" << filename
+                  << '"' << std::endl;
+        return;
+      }
+      value = static_cast<float>(int_input) / max_value;
+      data_.push_back(std::round(value * 255.0F));
+    }
+  } else if (str_input.compare("P5") == 0) {
+    // data stored in raw format
+
+    // get width
+    ifs >> int_input;
+    if (!ifs.good() || int_input <= 0) {
+      std::cout << "ERROR: Failed to parse file (PGM width) \"" << filename
+                << '"' << std::endl;
+      return;
+    }
+    width_ = int_input;
+
+    // get height
+    ifs >> int_input;
+    if (!ifs.good() || int_input <= 0) {
+      std::cout << "ERROR: Failed to parse file (PGM height) \"" << filename
+                << '"' << std::endl;
+      return;
+    }
+    height_ = int_input;
+
+    // get max_value
+    ifs >> int_input;
+    if (!ifs.good() || int_input <= 0) {
+      std::cout << "ERROR: Failed to parse file (PGM max) \"" << filename << '"'
+                << std::endl;
+      return;
+    }
+    int max_value_int = int_input;
+    float max_value = int_input;
+
+    // validate max_value
+    if (max_value_int != 255 && max_value_int != 65535) {
+      std::cout << "ERROR: Invalid max value for PGM (should be 255 or 65535) "
+                   "(filename \""
+                << filename << "\")" << std::endl;
+      return;
+    }
+
+    // extract whitespace before data
+    {
+      int c = ifs.get();
+      if (c != '\n' && c != ' ') {
+        std::cout << "WARNING: File data after PGM max is not whitespace "
+                     "(filename \""
+                  << filename << "\")"
+                  << " value is " << c << std::endl;
+      }
+
+      if (!ifs.good()) {
+        std::cout << "ERROR: Failed to parse file (PGM after whitespace) \""
+                  << filename << '"' << std::endl;
+        return;
+      }
+    }
+
+    // parse raw data
+    data_.clear();
+    data_.reserve(width_ * height_);
+    float value;
+    for (unsigned int i = 0; i < width_ * height_; ++i) {
+      if (max_value_int == 255) {
+        value = ifs.get() / max_value;
+        data_.push_back(std::round(value * 255.0F));
+        if (!ifs.good()) {
+          std::cout << "ERROR: Failed to parse file (PGM data) \"" << filename
+                    << '"' << std::endl;
+          return;
+        }
+      } else /* if (max_value_int == 65535) */ {
+        value = (ifs.get() & 0xFF) | ((ifs.get() << 8) & 0xFF00);
+        value /= max_value;
+        data_.push_back(std::round(value * 255.0F));
+        if (!ifs.good()) {
+          std::cout << "ERROR: Failed to parse file (PGM data 16-bit) \""
+                    << filename << '"' << std::endl;
+          return;
+        }
+      }
+    }
+
+    if (ifs.get() != decltype(ifs)::traits_type::eof()) {
+      std::cout << "WARNING: Trailing data in PGM file \"" << filename << '"'
+                << std::endl;
+    }
+  } else {
+    std::cout << "ERROR: Invalid \"magic number\" in header of file \""
+              << filename << '"' << std::endl;
+  }
+}
+
+void Image::DecodePPM(const std::string &filename) {
+  is_grayscale_ = false;
+  std::ifstream ifs(filename);
+  if (!ifs.is_open()) {
+    std::cout << "ERROR: Failed to open file \"" << filename << '"'
+              << std::endl;
+    return;
+  }
+
+  std::string str_input;
+  int int_input;
+  ifs >> str_input;
+  if (!ifs.good()) {
+    std::cout << "ERROR: Failed to parse file (PPM first identifier) \""
+              << filename << '"' << std::endl;
+    return;
+  }
+
+  if (str_input.compare("P3") == 0) {
+    // data stored in ascii format
+
+    // get width
+    ifs >> int_input;
+    if (!ifs.good() || int_input <= 0) {
+      std::cout << "ERROR: Failed to parse file (PPM width) \"" << filename
+                << '"' << std::endl;
+      return;
+    }
+    width_ = int_input;
+
+    // get height
+    ifs >> int_input;
+    if (!ifs.good() || int_input <= 0) {
+      std::cout << "ERROR: Failed to parse file (PPM height) \"" << filename
+                << '"' << std::endl;
+      return;
+    }
+    height_ = int_input;
+
+    // get max_value
+    ifs >> int_input;
+    if (!ifs.good() || int_input <= 0) {
+      std::cout << "ERROR: Failed to parse file (PPM max) \"" << filename << '"'
+                << std::endl;
+      return;
+    }
+    float max_value = int_input;
+
+    // parse data
+    data_.clear();
+    data_.reserve(width_ * height_ * 4);
+    float value;
+    for (unsigned int i = 0; i < width_ * height_ * 3; ++i) {
+      ifs >> int_input;
+      if (!ifs.good()) {
+        std::cout << "ERROR: Failed to parse file (PPM data) \"" << filename
+                  << '"' << std::endl;
+        return;
+      }
+      value = static_cast<float>(int_input) / max_value;
+      data_.push_back(std::round(value * 255.0F));
+      if (i % 3 == 2) {
+        // PPM is RGB but Image stores as RGBA
+        data_.push_back(255);
+      }
+    }
+  } else if (str_input.compare("P6") == 0) {
+    // data stored in raw format
+
+    // get width
+    ifs >> int_input;
+    if (!ifs.good() || int_input <= 0) {
+      std::cout << "ERROR: Failed to parse file (PPM width) \"" << filename
+                << '"' << std::endl;
+      return;
+    }
+    width_ = int_input;
+
+    // get height
+    ifs >> int_input;
+    if (!ifs.good() || int_input <= 0) {
+      std::cout << "ERROR: Failed to parse file (PPM height) \"" << filename
+                << '"' << std::endl;
+      return;
+    }
+    height_ = int_input;
+
+    // get max_value
+    ifs >> int_input;
+    if (!ifs.good() || int_input <= 0) {
+      std::cout << "ERROR: Failed to parse file (PPM max) \"" << filename << '"'
+                << std::endl;
+      return;
+    }
+    int max_value_int = int_input;
+    float max_value = int_input;
+
+    // validate max_value
+    if (max_value_int != 255 && max_value_int != 65535) {
+      std::cout << "ERROR: Invalid max value for PPM (should be 255 or 65535) "
+                   "(filename \""
+                << filename << "\")" << std::endl;
+      return;
+    }
+
+    // extract whitespace before data
+    {
+      int c = ifs.get();
+      if (c != '\n' && c != ' ') {
+        std::cout
+            << "WARNING: File data after PPM max is not whitespace (filename \""
+            << filename << "\") value is " << c << std::endl;
+      }
+
+      if (!ifs.good()) {
+        std::cout << "ERROR: Failed to parse file (PPM after whitespace) \""
+                  << filename << '"' << std::endl;
+        return;
+      }
+    }
+
+    // parse raw data
+    data_.clear();
+    data_.reserve(width_ * height_ * 4);
+    float value;
+    for (unsigned int i = 0; i < width_ * height_ * 3; ++i) {
+      if (max_value_int == 255) {
+        value = ifs.get() / max_value;
+        data_.push_back(std::round(value * 255.0F));
+        if (!ifs.good()) {
+          std::cout << "ERROR: Failed to parse file (PPM data) \"" << filename
+                    << '"' << std::endl;
+          return;
+        }
+      } else /* if (max_value_int == 65535) */ {
+        value = (ifs.get() & 0xFF) | ((ifs.get() << 8) & 0xFF00);
+        value /= max_value;
+        data_.push_back(std::round(value * 255.0F));
+        if (!ifs.good()) {
+          std::cout << "ERROR: Failed to parse file (PPM data 16-bit) \""
+                    << filename << '"' << std::endl;
+          return;
+        }
+      }
+
+      if (i % 3 == 2) {
+        // PPM is RGB but Image stores as RGBA
+        data_.push_back(255);
+      }
+    }
+
+    if (ifs.get() != decltype(ifs)::traits_type::eof()) {
+      std::cout << "WARNING: Trailing data in PPM file \"" << filename << '"'
+                << std::endl;
+    }
+  } else {
+    std::cout << "ERROR: Invalid \"magic number\" in header of file \""
+              << filename << '"' << std::endl;
+  }
+}