如何使用PIL调整大小并应用EXIF旋转信息？

Question

我想用Python来调整图片的大小。我的相机拍的照片都是横着的。

照片里面有一些EXIF信息，这些信息会告诉图片查看器应该怎么旋转图片。

但是大多数浏览器并不理解这些信息，所以我想用这些EXIF信息来旋转图片，同时保留其他的EXIF信息。

你知道我该怎么用Python做到这一点吗？

我查看了EXIF.py的源代码，发现了这样的内容：

0x0112: ('Orientation',
         {1: 'Horizontal (normal)',
          2: 'Mirrored horizontal',
          3: 'Rotated 180',
          4: 'Mirrored vertical',
          5: 'Mirrored horizontal then rotated 90 CCW',
          6: 'Rotated 90 CW',
          7: 'Mirrored horizontal then rotated 90 CW',
          8: 'Rotated 90 CCW'})

我该怎么用这些信息和PIL来实现呢？

Answer 1

首先，你得确认你的相机真的有旋转传感器。很多没有这个传感器的相机，拍出来的所有照片都会把方向标记设置为1（横向）。

接下来，我建议你使用pyexiv2和pyjpegtran这两个工具。PIL不支持无损旋转，而这正是pyjpegtran的强项。pyexiv2是一个可以让你把一张图片的元数据复制到另一张图片上的库（我记得它的方法叫copyMetadata）。

你确定在浏览器里展示照片之前不想先调整一下照片的大小吗？一张800万像素的JPEG照片对于浏览器窗口来说太大了，会导致加载时间非常长。

Answer 2

虽然PIL可以读取EXIF元数据，但它不能修改这些数据并把它们写回到图像文件中。

一个更好的选择是pyexiv2这个库。使用这个库，调整照片的方向非常简单。下面是一个例子：

import sys
import pyexiv2

image = pyexiv2.Image(sys.argv[1])
image.readMetadata()

image['Exif.Image.Orientation'] = 6
image.writeMetadata()

这段代码将方向设置为6，表示“顺时针旋转90度”。

Answer 3

我最终使用了 pyexiv2，不过在GNU以外的平台上安装起来有点麻烦。

#!/usr/bin/python
# -*- coding: utf-8 -*-
# Copyright (C) 2008-2009 Rémy HUBSCHER <natim@users.sf.net> - http://www.trunat.fr/portfolio/python.html

# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.

# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

# Using :
#   - Python Imaging Library PIL    http://www.pythonware.com/products/pil/index.htm
#   - pyexiv2                       http://tilloy.net/dev/pyexiv2/

###
# What is doing this script ?
#
#  1. Take a directory of picture from a Reflex Camera (Nikon D90 for example)
#  2. Use the EXIF Orientation information to turn the image
#  3. Remove the thumbnail from the EXIF Information
#  4. Create 2 image one maxi map in 600x600, one mini map in 200x200
#  5. Add a comment with the name of the Author and his Website
#  6. Copy the EXIF information to the maxi and mini image
#  7. Name the image files with a meanful name (Date of picture)

import os, sys
try:
    import Image
except:
    print "To use this program, you need to install Python Imaging Library - http://www.pythonware.com/products/pil/"
    sys.exit(1)

try:
    import pyexiv2
except:
    print "To use this program, you need to install pyexiv2 - http://tilloy.net/dev/pyexiv2/"
    sys.exit(1)

############# Configuration ##############
size_mini = 200, 200
size_maxi = 1024, 1024

# Information about the Photograph should be in ASCII
COPYRIGHT="Remy Hubscher - http://www.trunat.fr/"
ARTIST="Remy Hubscher"
##########################################

def listJPEG(directory):
    "Retourn a list of the JPEG files in the directory"
    fileList = [os.path.normcase(f) for f in os.listdir(directory)]
    fileList = [f for f in fileList if os.path.splitext(f)[1]  in ('.jpg', '.JPG')]
    fileList.sort()
    return fileList

def _mkdir(newdir):
    """
    works the way a good mkdir should :)
      - already exists, silently complete
      - regular file in the way, raise an exception
      - parent directory(ies) does not exist, make them as well
    """
    if os.path.isdir(newdir):
        pass
    elif os.path.isfile(newdir):
        raise OSError("a file with the same name as the desired " \
                      "dir, '%s', already exists." % newdir)
    else:
        head, tail = os.path.split(newdir)
        if head and not os.path.isdir(head):
            _mkdir(head)
        if tail:
            os.mkdir(newdir)

if len(sys.argv) < 3:
    print "USAGE : python %s indir outdir [comment]" % sys.argv[0]
    exit

indir  = sys.argv[1]
outdir = sys.argv[2]

if len(sys.argv) == 4:
    comment = sys.argv[1]
else:
    comment = COPYRIGHT

agrandie = os.path.join(outdir, 'agrandie')
miniature = os.path.join(outdir, 'miniature')

print agrandie, miniature

_mkdir(agrandie)
_mkdir(miniature)

for infile in listJPEG(indir):
    mini  = os.path.join(miniature, infile)
    grand = os.path.join(agrandie, infile)
    file_path = os.path.join(indir, infile)

    image = pyexiv2.Image(file_path)
    image.readMetadata()

    # We clean the file and add some information
    image.deleteThumbnail()

    image['Exif.Image.Artist'] = ARTIST
    image['Exif.Image.Copyright'] = COPYRIGHT

    image.setComment(comment)

    # I prefer not to modify the input file
    # image.writeMetadata()

    # We look for a meanful name
    if 'Exif.Image.DateTime' in image.exifKeys():
        filename = image['Exif.Image.DateTime'].strftime('%Y-%m-%d_%H-%M-%S.jpg')
        mini  = os.path.join(miniature, filename)
        grand = os.path.join(agrandie, filename)
    else:
        # If no exif information, leave the old name
        mini  = os.path.join(miniature, infile)
        grand = os.path.join(agrandie, infile)

    # We create the thumbnail
    #try:
    im = Image.open(file_path)
    im.thumbnail(size_maxi, Image.ANTIALIAS)

    # We rotate regarding to the EXIF orientation information
    if 'Exif.Image.Orientation' in image.exifKeys():
        orientation = image['Exif.Image.Orientation']
        if orientation == 1:
            # Nothing
            mirror = im.copy()
        elif orientation == 2:
            # Vertical Mirror
            mirror = im.transpose(Image.FLIP_LEFT_RIGHT)
        elif orientation == 3:
            # Rotation 180°
            mirror = im.transpose(Image.ROTATE_180)
        elif orientation == 4:
            # Horizontal Mirror
            mirror = im.transpose(Image.FLIP_TOP_BOTTOM)
        elif orientation == 5:
            # Horizontal Mirror + Rotation 90° CCW
            mirror = im.transpose(Image.FLIP_TOP_BOTTOM).transpose(Image.ROTATE_90)
        elif orientation == 6:
            # Rotation 270°
            mirror = im.transpose(Image.ROTATE_270)
        elif orientation == 7:
            # Horizontal Mirror + Rotation 270°
            mirror = im.transpose(Image.FLIP_TOP_BOTTOM).transpose(Image.ROTATE_270)
        elif orientation == 8:
            # Rotation 90°
            mirror = im.transpose(Image.ROTATE_90)

        # No more Orientation information
        image['Exif.Image.Orientation'] = 1
    else:
        # No EXIF information, the user has to do it
        mirror = im.copy()

    mirror.save(grand, "JPEG", quality=85)
    img_grand = pyexiv2.Image(grand)
    img_grand.readMetadata()
    image.copyMetadataTo(img_grand)
    img_grand.writeMetadata()
    print grand

    mirror.thumbnail(size_mini, Image.ANTIALIAS)
    mirror.save(mini, "JPEG", quality=85)
    img_mini = pyexiv2.Image(mini)
    img_mini.readMetadata()
    image.copyMetadataTo(img_mini)
    img_mini.writeMetadata()
    print mini

    print

如果你发现有什么可以改进的地方（除了它仍然只支持Python 2.5），请告诉我。