def scaleImage(image, width=None, height=None, direction="down",
quality=88, result=None):
"""Scale an image to another size.
The generated image is a JPEG image, unless the original is a PNG
image. This is needed to make sure alpha channel information is
not lost, which JPEG does not support.
Three different scaling options are supported:
* `up` scaling scales the smallest dimension up to the required size
and scrops the other dimension if needed.
* `down` scaling starts by scaling the largest dimension to the required
size and scrops the other dimension if needed.
* `thumbnail` scales to the requested dimensions without cropping. The
resulting image may have a different size than requested. This option
requires both width and height to be specified. `keep` is accepted as
an alternative spelling for this option, but its use is deprecated.
The `image` parameter can either be the raw image data (ie a `str`
instance) or an open file.
The `quality` parameter can be used to set the quality of the
resulting image scales.
The return value is a tuple with the new image, the image format and
a size-tuple. Optionally a file-like object can be given as the
`result` parameter, in which the generated image scale will be stored.
"""
if direction=="keep":
direction="thumbnail"
if direction=="thumbnail" and not (width and height):
raise ValueError("Thumbnailing requires both width and height to be specified")
elif width is None and height is None:
raise ValueError("Either width or height need to be given")
if isinstance(image, str):
image=StringIO(image)
image=PIL.Image.open(image)
if image.mode=="1":
# Convert black&white to grayscale
image=image.convert("L")
elif image.mode=="P":
# Convert palette based images to 3x8bit+alpha
image=image.convert("RGBA")
elif image.mode=="CMYK":
# Convert CMYK to RGB, allowing for web previews of print images
image=image.convert("RGB")
# When we create a new image during scaling we loose the format
# information, so remember it here.
image_format=image.format
current_size=image.size
# Determine scale factor needed to get the right height
if height is None:
scale_height=None
else:
scale_height=(float(height)/float(current_size[1]))
if width is None:
scale_width=None
else:
scale_width=(float(width)/float(current_size[0]))
if scale_height==scale_width or direction=="thumbnail":
# The original already has the right aspect ratio, so we only need
# to scale.
image.thumbnail((width, height), PIL.Image.ANTIALIAS)
else:
if direction=="down":
if scale_height is None or (scale_width is not None and scale_width>scale_height):
# Width is the smallest dimension (relatively), so scale up
# to the desired width
new_width=width
new_height=int(round(current_size[1]*scale_width))
else:
new_height=height
new_width=int(round(current_size[0]*scale_height))
else:
if scale_height is None or (scale_width is not None and scale_width<scale_height):
# Width is the largest dimension (relatively), so scale up
# to the desired width
new_width=width
new_height=int(round(current_size[1]*scale_width))
else:
new_height=height
new_width=int(round(current_size[0]*scale_height))
image.draft(image.mode, (new_width, new_height))
image=image.resize((new_width, new_height), PIL.Image.ANTIALIAS)
if (width is not None and new_width>width) or (height is not None and new_height>height):
if width is None:
left=0
right=new_width
else:
left=int((new_width-width)/2.0)
right=left+width
if height is None:
height=new_height
image=image.crop((left, 0, right, height))
if image_format=="PNG":
format="PNG"
else:
format="JPEG"
if result is None:
result=StringIO()
image.save(result, format, quality=quality, optimize=True)
result=result.getvalue()
else:
image.save(result, format, quality=quality, optimize=True)
result.seek(0)
return (result, format, image.size)
