在上传到Amazon S3之前，从Django模型表单调整图像大小

Question

我正在尝试在把图片上传到S3存储桶之前，使用PIL来调整图片大小。
模型表单工作得很好，但就是图片没有被调整大小。

以下是我的模型：

class ImageDetail(models.Model):

    def upload_image(self, filename):
        return u'obj/{name}.{ext}'.format(            
            name = uuid.uuid4().hex,
            ext  = os.path.splitext(filename)[1].strip('.')
        )
    flag = models.IntegerField(default=0)
    view = models.IntegerField(default=0)
    title = models.CharField(max_length=500, help_text="Enter a small/suitable title")
    image = models.ImageField(upload_to = upload_image, 
                          help_text="Please ensure, image size is less than 1 MB")

视图文件，看起来是这样的：

form = ImageUploadForm(request.POST or None, request.FILES or None)
if form.is_valid() and request.POST:
    form_instance = form.save(commit=False)
    img = form_instance.image
    # process the image now
    if img.width > 300 or img.height > 200:
        IMG_TYPE = os.path.splitext(img.name)[1].strip('.').lower()
        if IMG_TYPE == 'jpeg':
            PIL_TYPE = 'jpeg'
            FILE_EXTENSION = 'jpeg'
        elif IMG_TYPE == 'jpg':
            PIL_TYPE = 'jpeg'
            FILE_EXTENSION = 'jpeg'
        elif IMG_TYPE == 'png':
            PIL_TYPE = 'png'
            FILE_EXTENSION = 'png'
        elif IMG_TYPE == 'gif':
            PIL_TYPE = 'gif'
            FILE_EXTENSION = 'gif'
        else:
            print 'Not a valid format'
            return
        im = Image.open(StringIO(img.read()))
        im.thumbnail((300, 180), Image.ANTIALIAS)
        #Save the image
        temp_handle = StringIO()
        im.save(temp_handle, PIL_TYPE)
        s3 = S3Custom()
        if not form_instance.image:
            return self.success(self.request, form, None, errors = 'Error while uploading the image')
        form_instance.save()

S3的自定义函数定义如下：

class S3Custom(object):
    conn = S3Connection(settings.AWS_ACCESS_KEY_ID, settings.AWS_SECRET_ACCESS_KEY)
    b = Bucket(conn, settings.AWS_STORAGE_BUCKET_NAME)
    k = Key(b)
    def upload_file(self, ruta, prefix):
        try:           
            self.k.key = '%s/%s' % (prefix, os.path.split(ruta)[-1])
            self.k.set_contents_from_filename(ruta)
            self.k.make_public()
        except Exception, e:
            print e
        return '%s%s' % (settings.S3_URL, self.k.key)

我已经安装了django-storage。问题是，图片上传得很顺利，但没有被正确调整大小。我可能漏掉了什么？在

im.save(temp_handle, PIL_TYPE)
s3 = S3Custom()
form_instance.save()

视图文件中我是不是做错了什么？请告诉我，谢谢！

django PIL s3 image processing model form image resizing

在上传到Amazon S3之前，从Django模型表单调整图像大小

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