尝试在 django 中创建缩略图时无法识别图像文件 [重复]答案

【问题标题】：getting Cannot identify image file when trying to create thumbnail in django [duplicate]尝试在 django 中创建缩略图时无法识别图像文件 [重复]
【发布时间】：2012-11-29 15:28:45
【问题描述】：

可能重复：
resize image on save

我正在尝试在 django 中创建缩略图，正在尝试构建一个专门用于生成缩略图的自定义类。如下

from cStringIO import StringIO
from PIL import Image

class Thumbnail(object):

    SIZE = (50, 50)

    def __init__(self, source):
        self.source = source
        self.output = None

    def generate(self, size=None, fit=True):
        if not size:
            size = self.SIZE

        if not isinstance(size, tuple):
            raise TypeError('Thumbnail class: The size parameter must be an instance of a tuple.')

        # resize properties
        box = size
        factor = 1
        image = Image.open(self.source)
        # Convert to RGB if necessary
        if image.mode not in ('L', 'RGB'): 
            image = image.convert('RGB')
        while image.size[0]/factor > 2*box[0] and image.size[1]*2/factor > 2*box[1]:
            factor *=2
        if factor > 1:
            image.thumbnail((image.size[0]/factor, image.size[1]/factor), Image.NEAREST)

        #calculate the cropping box and get the cropped part
        if fit:
            x1 = y1 = 0
            x2, y2 = image.size
            wRatio = 1.0 * x2/box[0]
            hRatio = 1.0 * y2/box[1]
            if hRatio > wRatio:
                y1 = int(y2/2-box[1]*wRatio/2)
                y2 = int(y2/2+box[1]*wRatio/2)
            else:
                x1 = int(x2/2-box[0]*hRatio/2)
                x2 = int(x2/2+box[0]*hRatio/2)
            image = image.crop((x1,y1,x2,y2))

        #Resize the image with best quality algorithm ANTI-ALIAS
        image.thumbnail(box, Image.ANTIALIAS)

        # save image to memory
        temp_handle = StringIO()
        image.save(temp_handle, 'png')
        temp_handle.seek(0)

        self.output = temp_handle

        return self

    def get_output(self):
        self.output.seek(0)
        return self.output.read()

课程的目的是让我可以在不同的位置使用它来动态生成缩略图。该类完美运行，我直接在视图下对其进行了测试。我在表单的保存方法中实现了缩略图类，以在保存时调整原始图像的大小。

在我的设计中，我有两个缩略图字段。我能够生成一个缩略图，如果我尝试生成两个它会崩溃并且我已经卡了几个小时不知道是什么问题。

这是我的模型

class Image(models.Model):
    article         = models.ForeignKey(Article)
    title           = models.CharField(max_length=100, null=True, blank=True)
    src             = models.ImageField(upload_to='publication/image/')
    r128            = models.ImageField(upload_to='publication/image/128/', blank=True, null=True)
    r200            = models.ImageField(upload_to='publication/image/200/', blank=True, null=True)

    uploaded_at     = models.DateTimeField(auto_now=True)

这是我的表格

class ImageForm(models.ModelForm):
    """

    """
    class Meta:
        model = Image
        fields = ('src',)


    def save(self, commit=True):
        instance = super(ImageForm, self).save(commit=True)


        instance.r128 = SimpleUploadedFile(
                    instance.src.name,
                    Thumbnail(instance.src).generate((128, 128)).get_output(),
                    content_type='image/png'
                )


        instance.r200 = SimpleUploadedFile(
            instance.src.name,
            Thumbnail(instance.src).generate((200, 200)).get_output(),
            content_type='image/png'
        )

        if commit:
            instance.save()
        return instance

奇怪的是，当我在保存表单中删除包含 instance.r200 的行时。它工作正常，它会生成缩略图并成功存储它。一旦我添加了第二个缩略图，它就会失败..

有什么想法在这里做错了吗？

谢谢

更新：

根据评论请求，我正在附加错误跟踪

IOError at /en/publication/new/

cannot identify image file

Request Method:     POST
Request URL:    http://127.0.0.1:8000/en/publication/new/?image-extra=
Django Version:     1.4.2
Exception Type:     IOError
Exception Value:    

cannot identify image file

Exception Location:     /Users/mo/Projects/pythonic/snowflake-env/lib/python2.7/site-packages/PIL/Image.py in open, line 1980
Python Executable:  /Users/mo/Projects/pythonic/snowflake-env/bin/python
Python Version:     2.7.2

更新

尝试创建打印语句，下面是输出

Source: publication/image/tumblr_m9o7244nZM1rykg1io1_1280_11.jpg
Source: publication/image/tumblr_m9o7244nZM1rykg1io1_1280_11.jpg
ERROR:root:cannot identify image file
ERROR:django.request:Internal Server Error: /en/publication/new/
Traceback (most recent call last):
  File "/Users/mo/Projects/pythonic/snowflake-env/lib/python2.7/site-packages/django/core/handlers/base.py", line 111, in get_response
    response = callback(request, *callback_args, **callback_kwargs)
  File "/Users/mo/Projects/pythonic/snowflake-env/lib/python2.7/site-packages/django/contrib/auth/decorators.py", line 20, in _wrapped_view
    return view_func(request, *args, **kwargs)
  File "/Users/mo/Projects/pythonic/snowflake-env/lib/python2.7/site-packages/django/db/transaction.py", line 209, in inner
    return func(*args, **kwargs)
  File "/Users/mo/Projects/pythonic/snowflake-env/snowflake/snowflake/apps/publication/views.py", line 69, in new
    formset.save()
  File "/Users/mo/Projects/pythonic/snowflake-env/lib/python2.7/site-packages/django/forms/models.py", line 497, in save
    return self.save_existing_objects(commit) + self.save_new_objects(commit)
  File "/Users/mo/Projects/pythonic/snowflake-env/lib/python2.7/site-packages/django/forms/models.py", line 628, in save_new_objects
    self.new_objects.append(self.save_new(form, commit=commit))
  File "/Users/mo/Projects/pythonic/snowflake-env/lib/python2.7/site-packages/django/forms/models.py", line 727, in save_new
    obj = form.save(commit=False)
  File "/Users/mo/Projects/pythonic/snowflake-env/snowflake/snowflake/apps/publication/forms.py", line 113, in save
    Thumbnail(instance.src).generate((200, 200)).get_output(),
  File "/Users/mo/Projects/pythonic/snowflake-env/snowflake/snowflake/apps/core/utils.py", line 23, in generate
    image = Image.open(self.source)
  File "/Users/mo/Projects/pythonic/snowflake-env/lib/python2.7/site-packages/PIL/Image.py", line 1980, in open
    raise IOError("cannot identify image file")
IOError: cannot identify image file

如图所示，第一张图片打印成功，第二张图片处理失败。

更新

在缩略图类中应用 copy() 后追溯错误更新

ERROR:root:cannot identify image file
ERROR:django.request:Internal Server Error: /en/publication/new/
Traceback (most recent call last):
  File "/Users/mo/Projects/pythonic/snowflake-env/lib/python2.7/site-packages/django/core/handlers/base.py", line 111, in get_response
    response = callback(request, *callback_args, **callback_kwargs)
  File "/Users/mo/Projects/pythonic/snowflake-env/lib/python2.7/site-packages/django/contrib/auth/decorators.py", line 20, in _wrapped_view
    return view_func(request, *args, **kwargs)
  File "/Users/mo/Projects/pythonic/snowflake-env/lib/python2.7/site-packages/django/db/transaction.py", line 209, in inner
    return func(*args, **kwargs)
  File "/Users/mo/Projects/pythonic/snowflake-env/snowflake/snowflake/apps/publication/views.py", line 69, in new
    formset.save()
  File "/Users/mo/Projects/pythonic/snowflake-env/lib/python2.7/site-packages/django/forms/models.py", line 497, in save
    return self.save_existing_objects(commit) + self.save_new_objects(commit)
  File "/Users/mo/Projects/pythonic/snowflake-env/lib/python2.7/site-packages/django/forms/models.py", line 628, in save_new_objects
    self.new_objects.append(self.save_new(form, commit=commit))
  File "/Users/mo/Projects/pythonic/snowflake-env/lib/python2.7/site-packages/django/forms/models.py", line 727, in save_new
    obj = form.save(commit=False)
  File "/Users/mo/Projects/pythonic/snowflake-env/snowflake/snowflake/apps/publication/forms.py", line 113, in save
    f128.write(Thumbnail(instance.src).generate((128, 128)).get_output())
  File "/Users/mo/Projects/pythonic/snowflake-env/snowflake/snowflake/apps/core/utils.py", line 15, in __init__
    self._pilImage = Image.open(self.source)
  File "/Users/mo/Projects/pythonic/snowflake-env/lib/python2.7/site-packages/PIL/Image.py", line 1980, in open
    raise IOError("cannot identify image file")
IOError: cannot identify image file

更新

最后，我设法让它工作，但我不得不将文件流式传输到 self.source 作为 belo

def __init__(self, source):
    self.source = StringIO(file(source.path, "rb").read())
    self.output = None

    self._pilImage = Image.open(self.source)

以上是理想的方法吗？每次点击时读取文件是个好主意吗？如果没有，我的替代方案是什么？

【问题讨论】：

P.S 得到的错误是“无法识别图像文件”
您不使用django-stdimage的原因是什么？
不使用stdimage的原因是因为我裁剪图像不仅实现了..我不知道重复，我认为它与缩略图类有关..
你的课写得很奇怪。另外，包括您的回溯
我只是在帖子后面附加了回溯

标签： python django python-imaging-library

【解决方案1】：

我看到的问题在于您设计 Thumbnail 类的方式。它使用类属性来存储实例变量，这意味着当您尝试多次使用该类时会发生冲突。

不需要静态的load 方法，因为一旦将属性移动到实例，它的作用就与类的构造函数完全相同。通过在构造函数中要求source，您可以确保稍后在generate 中查找空字符串值时不会发生崩溃。

另外，我认为您面临的主要问题之一是，当您使用 django 模型为ImageField 返回的类文件对象包装器时。如果您传入字符串路径，则不会看到这一点，但当您传入文件对象时，generate 方法会将其读取到最后。然后你用同一个源对象第二次调用generate，但它在最后，你得到一个IOError。现在一种方法是确保在再次调用Thumbnail 之前将源返回0，但是您可以省去麻烦，只需打开Thumbnail 类并缓存一次PIL 图像构造函数。那么generate就不需要每次都不断地重读一遍了。

# Example from your code #
def generate(self, size=None, fit=True):
    ...
    # The first time you do this, it will read
    # self.source to the end, because in Django, you
    # are passing a file-like object.
    image = Image.open(self.source)

# this will work the first time
generate()
# uh oh. self.source was a file object that is at the end
generate() # crash

重写的缩略图类

from cStringIO import StringIO
from PIL import Image

class Thumbnail(object):

    SIZE = (50, 50)

    def __init__(self, source):
        self.source = source
        self.output = None

        self._pilImage = Image.open(self.source)

    def generate(self, size=None, fit=True):
        if not size:
            size = self.SIZE

        if not isinstance(size, tuple):
            raise TypeError('Thumbnail class: The size parameter must be an instance of a tuple.')

        # resize properties
        box = size
        factor = 1
        image = self._pilImage.copy()

        # Convert to RGB if necessary
        if image.mode not in ('L', 'RGB'): 
            image = image.convert('RGB')
        while image.size[0]/factor > 2*box[0] and image.size[1]*2/factor > 2*box[1]:
            factor *=2
        if factor > 1:
            image.thumbnail((image.size[0]/factor, image.size[1]/factor), Image.NEAREST)

        #calculate the cropping box and get the cropped part
        if fit:
            x1 = y1 = 0
            x2, y2 = image.size
            wRatio = 1.0 * x2/box[0]
            hRatio = 1.0 * y2/box[1]
            if hRatio > wRatio:
                y1 = int(y2/2-box[1]*wRatio/2)
                y2 = int(y2/2+box[1]*wRatio/2)
            else:
                x1 = int(x2/2-box[0]*hRatio/2)
                x2 = int(x2/2+box[0]*hRatio/2)
            image = image.crop((x1,y1,x2,y2))

        #Resize the image with best quality algorithm ANTI-ALIAS
        image.thumbnail(box, Image.ANTIALIAS)

        # save image to memory
        temp_handle = StringIO()
        image.save(temp_handle, 'png')
        temp_handle.seek(0)

        self.output = temp_handle

        return self

    def get_output(self):
        self.output.seek(0)
        return self.output.read()

用法：Thumbnail(src).generate((200, 200)).get_output()

source 和 output 对于每个实例都必须是唯一的。但在您的版本中，您会将output 设置为类级别，这意味着Thumbnail 的两个实例使用output 的共享最新版本。

# your code #
    # this is assigning the most recently processed
    # object to the class level. shared among all.
    self.output = temp_handle

    return self

def get_output(self):
    # always read the shared class level
    return self.output.read()

另外，我觉得有一种更简单的方法来执行您的调整大小/适合/裁剪。如果您解释要对图像进行的确切转换，我也可以简化它。

更新

我忘了特别提到我建议保存一次源图像，你的用法应该是这样的：

def save(self, commit=True):
    instance = super(ImageForm, self).save(commit=True)

    thumb = Thumbnail(instance.src)

    instance.r128 = SimpleUploadedFile(
        instance.src.name,
        thumb.generate((128, 128)).get_output(),
        content_type='image/png'
    )

    instance.r200 = SimpleUploadedFile(
        instance.src.name,
        thumb.generate((200, 200)).get_output(),
        content_type='image/png'
    )

请注意，我们只使用源创建了一个Thumbnail 实例，它只会在 PIL 中打开一次。然后，您可以从中生成任意数量的图像。

【讨论】：

您好 jdi，非常感谢您的详细说明，感谢您花费的时间。然而，我仍然面临同样的错误，我复制了你提出的完全相同的代码，但问题相同。我开始怀疑问题出在 forms.save() 方法上。通过观察，您认为这可能是问题所在吗？
之所以怀疑 forms.save() 方法，是因为我只是尝试在视图中使用缩略图类来呈现带有图像的 HttpResponse 并将其作为 png 的 memtype。我尝试生成两个和三个缩略图，然后只重新调整最后一个，它起作用了。那么，这是否意味着 forms.save() 或模型不接受
我刚刚用正在使用的最新代码和回溯错误更新了问题
你能帮我一个忙，在Image.open(self.source)这一行之前写一个打印声明，在你的Thumbnail类中：print "Source:", self.source。我很好奇你真正传递给 PIL 的是什么
我打印了，我得到了以下来源：publication/image/1207281205471202-tonylawfirmpic_33.jpg

【解决方案2】：

PIL.Image.open(...)的参数可以是文件名，也可以是文件对象。如果使用类似对象的文件，则读取位置应位于文件的开头。您使用文件对象。（这是肯定的，因为你使用了instance.src.name，然后你通过了Thumbnail(instance.src)。）

解决方案：在创建第二个缩略图之前将文件倒回到开头instance.src.seek(0)，或者只传递文件名，而不是文件对象：Thumbnail(instance.src.name)。

【讨论】：