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# -*- coding: utf-8 -*-
# Copyright 2014-2016 OpenMarket Ltd
#
# 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 logging
from io import BytesIO
from PIL import Image
logger = logging.getLogger(__name__)
EXIF_ORIENTATION_TAG = 0x0112
EXIF_TRANSPOSE_MAPPINGS = {
2: Image.FLIP_LEFT_RIGHT,
3: Image.ROTATE_180,
4: Image.FLIP_TOP_BOTTOM,
5: Image.TRANSPOSE,
6: Image.ROTATE_270,
7: Image.TRANSVERSE,
8: Image.ROTATE_90,
}
class ThumbnailError(Exception):
"""An error occurred generating a thumbnail."""
class Thumbnailer:
FORMATS = {"image/jpeg": "JPEG", "image/png": "PNG"}
def __init__(self, input_path):
try:
self.image = Image.open(input_path)
except OSError as e:
# If an error occurs opening the image, a thumbnail won't be able to
# be generated.
raise ThumbnailError from e
self.width, self.height = self.image.size
self.transpose_method = None
try:
# We don't use ImageOps.exif_transpose since it crashes with big EXIF
image_exif = self.image._getexif()
if image_exif is not None:
image_orientation = image_exif.get(EXIF_ORIENTATION_TAG)
self.transpose_method = EXIF_TRANSPOSE_MAPPINGS.get(image_orientation)
except Exception as e:
# A lot of parsing errors can happen when parsing EXIF
logger.info("Error parsing image EXIF information: %s", e)
def transpose(self):
"""Transpose the image using its EXIF Orientation tag
Returns:
Tuple[int, int]: (width, height) containing the new image size in pixels.
"""
if self.transpose_method is not None:
self.image = self.image.transpose(self.transpose_method)
self.width, self.height = self.image.size
self.transpose_method = None
# We don't need EXIF any more
self.image.info["exif"] = None
return self.image.size
def aspect(self, max_width, max_height):
"""Calculate the largest size that preserves aspect ratio which
fits within the given rectangle::
(w_in / h_in) = (w_out / h_out)
w_out = min(w_max, h_max * (w_in / h_in))
h_out = min(h_max, w_max * (h_in / w_in))
Args:
max_width: The largest possible width.
max_height: The largest possible height.
"""
if max_width * self.height < max_height * self.width:
return max_width, (max_width * self.height) // self.width
else:
return (max_height * self.width) // self.height, max_height
def _resize(self, width, height):
# 1-bit or 8-bit color palette images need converting to RGB
# otherwise they will be scaled using nearest neighbour which
# looks awful
if self.image.mode in ["1", "P"]:
self.image = self.image.convert("RGB")
return self.image.resize((width, height), Image.ANTIALIAS)
def scale(self, width, height, output_type):
"""Rescales the image to the given dimensions.
Returns:
BytesIO: the bytes of the encoded image ready to be written to disk
"""
scaled = self._resize(width, height)
return self._encode_image(scaled, output_type)
def crop(self, width, height, output_type):
"""Rescales and crops the image to the given dimensions preserving
aspect::
(w_in / h_in) = (w_scaled / h_scaled)
w_scaled = max(w_out, h_out * (w_in / h_in))
h_scaled = max(h_out, w_out * (h_in / w_in))
Args:
max_width: The largest possible width.
max_height: The largest possible height.
Returns:
BytesIO: the bytes of the encoded image ready to be written to disk
"""
if width * self.height > height * self.width:
scaled_height = (width * self.height) // self.width
scaled_image = self._resize(width, scaled_height)
crop_top = (scaled_height - height) // 2
crop_bottom = height + crop_top
cropped = scaled_image.crop((0, crop_top, width, crop_bottom))
else:
scaled_width = (height * self.width) // self.height
scaled_image = self._resize(scaled_width, height)
crop_left = (scaled_width - width) // 2
crop_right = width + crop_left
cropped = scaled_image.crop((crop_left, 0, crop_right, height))
return self._encode_image(cropped, output_type)
def _encode_image(self, output_image, output_type):
output_bytes_io = BytesIO()
fmt = self.FORMATS[output_type]
if fmt == "JPEG":
output_image = output_image.convert("RGB")
output_image.save(output_bytes_io, fmt, quality=80)
return output_bytes_io
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