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utils.py
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utils.py
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import os
import mimetypes
from StringIO import StringIO
import sys
import types
from django.core.files.base import ContentFile
from django.db.models.loading import cache
from django.utils.functional import wraps
from django.utils.encoding import smart_str, smart_unicode
from .lib import Image, ImageFile
RGBA_TRANSPARENCY_FORMATS = ['PNG']
PALETTE_TRANSPARENCY_FORMATS = ['PNG', 'GIF']
class IKContentFile(ContentFile):
"""
Wraps a ContentFile in a file-like object with a filename and a
content_type. A PIL image format can be optionally be provided as a content
type hint.
"""
def __init__(self, filename, content, format=None):
self.file = ContentFile(content)
self.file.name = filename
mimetype = getattr(self.file, 'content_type', None)
if format and not mimetype:
mimetype = format_to_mimetype(format)
if not mimetype:
ext = os.path.splitext(filename or '')[1]
mimetype = extension_to_mimetype(ext)
self.file.content_type = mimetype
def __str__(self):
return smart_str(self.file.name or '')
def __unicode__(self):
return smart_unicode(self.file.name or u'')
def img_to_fobj(img, format, autoconvert=True, **options):
return save_image(img, StringIO(), format, options, autoconvert)
def get_spec_files(instance):
try:
return instance._ik.spec_files
except AttributeError:
return []
def open_image(target):
target.seek(0)
img = Image.open(target)
img.copy = types.MethodType(_wrap_copy(img.copy), img, img.__class__)
return img
def _wrap_copy(f):
@wraps(f)
def copy(self):
img = f()
try:
img.app = self.app
except AttributeError:
pass
try:
img._getexif = self._getexif
except AttributeError:
pass
return img
return copy
class UnknownExtensionError(Exception):
pass
class UnknownFormatError(Exception):
pass
_pil_init = 0
def _preinit_pil():
"""Loads the standard PIL file format drivers. Returns True if ``preinit()``
was called (and there's a potential that more drivers were loaded) or False
if there is no possibility that new drivers were loaded.
"""
global _pil_init
if _pil_init < 1:
Image.preinit()
_pil_init = 1
return True
return False
def _init_pil():
"""Loads all PIL file format drivers. Returns True if ``init()`` was called
(and there's a potential that more drivers were loaded) or False if there is
no possibility that new drivers were loaded.
"""
global _pil_init
_preinit_pil()
if _pil_init < 2:
Image.init()
_pil_init = 2
return True
return False
def _extension_to_format(extension):
return Image.EXTENSION.get(extension.lower())
def _format_to_extension(format):
if format:
for k, v in Image.EXTENSION.iteritems():
if v == format.upper():
return k
return None
def extension_to_mimetype(ext):
try:
filename = 'a%s' % (ext or '') # guess_type requires a full filename, not just an extension
mimetype = mimetypes.guess_type(filename)[0]
except IndexError:
mimetype = None
return mimetype
def format_to_mimetype(format):
return extension_to_mimetype(format_to_extension(format))
def extension_to_format(extension):
"""Returns the format that corresponds to the provided extension.
"""
format = _extension_to_format(extension)
if not format and _preinit_pil():
format = _extension_to_format(extension)
if not format and _init_pil():
format = _extension_to_format(extension)
if not format:
raise UnknownExtensionError(extension)
return format
def format_to_extension(format):
"""Returns the first extension that matches the provided format.
"""
extension = None
if format:
extension = _format_to_extension(format)
if not extension and _preinit_pil():
extension = _format_to_extension(format)
if not extension and _init_pil():
extension = _format_to_extension(format)
if not extension:
raise UnknownFormatError(format)
return extension
def _get_models(apps):
models = []
for app_label in apps or []:
app = cache.get_app(app_label)
models += [m for m in cache.get_models(app)]
return models
def invalidate_app_cache(apps):
for model in _get_models(apps):
print 'Invalidating cache for "%s.%s"' % (model._meta.app_label, model.__name__)
for obj in model._default_manager.order_by('-pk'):
for f in get_spec_files(obj):
f.invalidate()
def validate_app_cache(apps, force_revalidation=False):
for model in _get_models(apps):
for obj in model._default_manager.order_by('-pk'):
model_name = '%s.%s' % (model._meta.app_label, model.__name__)
if force_revalidation:
print 'Invalidating & validating cache for "%s"' % model_name
else:
print 'Validating cache for "%s"' % model_name
for f in get_spec_files(obj):
if force_revalidation:
f.invalidate()
f.validate()
def suggest_extension(name, format):
original_extension = os.path.splitext(name)[1]
try:
suggested_extension = format_to_extension(format)
except UnknownFormatError:
extension = original_extension
else:
if suggested_extension.lower() == original_extension.lower():
extension = original_extension
else:
try:
original_format = extension_to_format(original_extension)
except UnknownExtensionError:
extension = suggested_extension
else:
# If the formats match, give precedence to the original extension.
if format.lower() == original_format.lower():
extension = original_extension
else:
extension = suggested_extension
return extension
def save_image(img, outfile, format, options=None, autoconvert=True):
"""
Wraps PIL's ``Image.save()`` method. There are two main benefits of using
this function over PIL's:
1. It gracefully handles the infamous "Suspension not allowed here" errors.
2. It prepares the image for saving using ``prepare_image()``, which will do
some common-sense processing given the target format.
"""
options = options or {}
if autoconvert:
img, save_kwargs = prepare_image(img, format)
options = dict(save_kwargs.items() + options.items())
# Attempt to reset the file pointer.
try:
outfile.seek(0)
except AttributeError:
pass
try:
with quiet():
img.save(outfile, format, **options)
except IOError:
# PIL can have problems saving large JPEGs if MAXBLOCK isn't big enough,
# So if we have a problem saving, we temporarily increase it. See
# http://github.com/jdriscoll/django-imagekit/issues/50
old_maxblock = ImageFile.MAXBLOCK
ImageFile.MAXBLOCK = img.size[0] * img.size[1]
try:
img.save(outfile, format, **options)
finally:
ImageFile.MAXBLOCK = old_maxblock
try:
outfile.seek(0)
except AttributeError:
pass
return outfile
class quiet(object):
"""
A context manager for suppressing the stderr activity of PIL's C libraries.
Based on http://stackoverflow.com/a/978264/155370
"""
def __enter__(self):
self.stderr_fd = sys.__stderr__.fileno()
self.null_fd = os.open(os.devnull, os.O_RDWR)
self.old = os.dup(self.stderr_fd)
os.dup2(self.null_fd, self.stderr_fd)
def __exit__(self, *args, **kwargs):
os.dup2(self.old, self.stderr_fd)
os.close(self.null_fd)
def prepare_image(img, format):
"""
Prepares the image for saving to the provided format by doing some
common-sense conversions. This includes things like preserving transparency
and quantizing. This function is used automatically by ``save_image()``
(and classes like ``ImageSpecField`` and ``ProcessedImageField``)
immediately before saving unless you specify ``autoconvert=False``. It is
provided as a utility for those doing their own processing.
:param img: The image to prepare for saving.
:param format: The format that the image will be saved to.
"""
matte = False
save_kwargs = {}
if img.mode == 'RGBA':
if format in RGBA_TRANSPARENCY_FORMATS:
pass
elif format in PALETTE_TRANSPARENCY_FORMATS:
# If you're going from a format with alpha transparency to one
# with palette transparency, transparency values will be
# snapped: pixels that are more opaque than not will become
# fully opaque; pixels that are more transparent than not will
# become fully transparent. This will not produce a good-looking
# result if your image contains varying levels of opacity; in
# that case, you'll probably want to use a processor to matte
# the image on a solid color. The reason we don't matte by
# default is because not doing so allows processors to treat
# RGBA-format images as a super-type of P-format images: if you
# have an RGBA-format image with only a single transparent
# color, and save it as a GIF, it will retain its transparency.
# In other words, a P-format image converted to an
# RGBA-formatted image by a processor and then saved as a
# P-format image will give the expected results.
# Work around a bug in PIL: split() doesn't check to see if
# img is loaded.
img.load()
alpha = img.split()[-1]
mask = Image.eval(alpha, lambda a: 255 if a <= 128 else 0)
img = img.convert('RGB').convert('P', palette=Image.ADAPTIVE,
colors=255)
img.paste(255, mask)
save_kwargs['transparency'] = 255
else:
# Simply converting an RGBA-format image to an RGB one creates a
# gross result, so we matte the image on a white background. If
# that's not what you want, that's fine: use a processor to deal
# with the transparency however you want. This is simply a
# sensible default that will always produce something that looks
# good. Or at least, it will look better than just a straight
# conversion.
matte = True
elif img.mode == 'P':
if format in PALETTE_TRANSPARENCY_FORMATS:
try:
save_kwargs['transparency'] = img.info['transparency']
except KeyError:
pass
elif format in RGBA_TRANSPARENCY_FORMATS:
# Currently PIL doesn't support any RGBA-mode formats that
# aren't also P-mode formats, so this will never happen.
img = img.convert('RGBA')
else:
matte = True
else:
img = img.convert('RGB')
# GIFs are always going to be in palette mode, so we can do a little
# optimization. Note that the RGBA sources also use adaptive
# quantization (above). Images that are already in P mode don't need
# any quantization because their colors are already limited.
if format == 'GIF':
img = img.convert('P', palette=Image.ADAPTIVE)
if matte:
img = img.convert('RGBA')
bg = Image.new('RGBA', img.size, (255, 255, 255))
bg.paste(img, img)
img = bg.convert('RGB')
if format == 'JPEG':
save_kwargs['optimize'] = True
return img, save_kwargs