Olaf Dietrich (2010-07-30T09:42:47+0200):
> Does the centering parameter of ImageOps.fit() really
> work as intended (i.e. as described in the documentation)?
Meanwhile, I've had a closer look at ImageOps.fit() and start to
understand what's going on:
# Returns a sized and cropped version of the image, cropped to the
# requested aspect ratio and size.
def fit(image, size, method=Image.NEAREST, bleed=0.0, centering=(0.5, 0.5)):
1) Cropping is always performed if the requested size ("size") has
another aspect ratio than the original image.size. In particular,
cropping is then performed even though the bleed-parameter
might be zero (the default).
2) If cropping is performed because of differing aspect ratios, then
it can be controlled by the centering-parameter.
3) If additional cropping is requested by setting the bleed-parameter
to a value >0 (and <0.5), then this additional border is always
removed symmetrically from the original image - this cannot
be influenced by the centering parameter (this is what I originally
expected the centering-parameter to do).
I guess this behavior might be sensible as well, so I do not
ask for any changes here.
4) (an independent observation:) There is a a wrong decrement by 1
when calculating the liveArea (or the liveSize).
So, I suggest to improve the documentation and to correct the
definition of liveArea, i.e., change
# @param size The requested output size in pixels, given as a
# (width, height) tuple.
to e.g.
# @param size The requested output size in pixels, given as a
# (width, height) tuple. If the aspect ratio of size differs
# from the original one, the image data is cropped appropriately.
Change
# @param centering Control the cropping position. Use (0.5, 0.5) for
# center cropping (e.g. if cropping the width, take 50% off of the
...
to e.g.
# @param centering Control the cropping position. This parameter is
# relevant only if a changed aspect ratio is requested by the chosen
# size. Any additionally removed border pixels (if bleed is > 0)
# are not influenced by the centering parameter, but are always
# removed symmetrically from the image. Use (0.5, 0.5) for
# center cropping (e.g. if cropping the width, take 50% off of the
...
And finally correct:
liveArea = (
bleedPixels[0], bleedPixels[1], image.size[0] - bleedPixels[0] - 1,
image.size[1] - bleedPixels[1] - 1
)
to
liveArea = (
bleedPixels[0], bleedPixels[1], image.size[0] - bleedPixels[0],
image.size[1] - bleedPixels[1]
)
Unfortunately, I was really looking for a function that does
asymmetric cropping of any border pixels as well, so I will
have to implement my own version of fit() ...
Olaf
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