ANTIALIAS vs BICUBIC in PIL(Python Image Library)?
Solution 1
These are listed in order of lowest to higest complexity. There will be visual differences between them. The main difference will be how long the algorithm takes to execute.
You'll have to decide what matters more to you, speed, or quality. If you're only doing 5 images, go for quality. If you're doing 100,000 images, maybe go for speed. It really depends on what you're using it for.
The 2x2 and 4x4 environment means that the algorithm looks at a 2x2 or 4x4 area of pixels.
Solution 2
ANTIALIAS
is no longer the proper term, it was replaced by LANCZOS
which is a more descriptive term for the algorithm used. You can still use ANTIALIAS
in your code for backward compatibility purposes but it's not recommended.
LANCZOS
uses a larger pattern than BICUBIC
and should produce slightly sharper results. It will also be slower.
The documentation has been changed since the question was asked, and the references to 2x2 or 4x4 have been removed. You probably weren't the only one confused by them.
resample – An optional resampling filter. This can be one of PIL.Image.NEAREST
(use nearest neighbour), PIL.Image.BILINEAR (linear interpolation),
PIL.Image.BICUBIC (cubic spline interpolation), or PIL.Image.LANCZOS (a high-quality
downsampling filter). If omitted, or if the image has mode “1” or “P”, it is set
PIL.Image.NEAREST.
The below is no longer valid, it was fixed in Pillow 2.7. I'm leaving it here for those with older versions, although I'd highly advise you to upgrade.
I've now gone through the source to figure out the details. I'm not terribly pleased by what I saw.
First, BICUBIC
. There are a number of formulas which can be classified as bicubic, the most common of these being the Catmull-Rom interpolation. That's not what PIL uses. Don Mitchell and Arun Netravali wrote a paper that analyzes all the variations and characterizes them using two variables B and C; the one used by PIL corresponds to B=0 and C=1. In the Mitchell-Netravali paper this is clearly in the Ringing artifact region. This means that enlarged images will have unnatural bright or dark halos around edges.
Next up is ANTIALIAS
. This is based on a Lanczos-3 filter, which would ordinarily be a good choice for both downsizing and upsizing. Unfortunately there's a bug in the code when upsizing - rather than taking in an area of 6x6 pixels to calculate the result, it's truncated at 2x2 pixels. This makes it barely better than bilinear.
Comments
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xunzhang almost 2 years
I am using PIL to resize my images, my case is to scale up the original image.
I am confused about the algorithm used with `resample=ANTIALIAS'.
According to the document below,
ANTIALIAS
seems to be the best while scaling down. I wonder In which case canBICUBIC
win?(some of my test case shows bicubic is better choice)An optional resampling filter. This can be one of NEAREST (use nearest neighbour), BILINEAR (linear interpolation in a 2x2 environment), BICUBIC (cubic spline interpolation in a 4x4 environment), or ANTIALIAS (a high-quality downsampling filter). If omitted, or if the image has mode “1” or “P”, it is set NEAREST.
I am also confused about the
linear interpolation in a 2x2 environment
andcubic spline interpolation in a 4x4 environment
in the document. What does it mean here?Thanks.
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xunzhang about 10 yearsin some of my test case, bicubic is the best. can u explain that?
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aglassman about 10 yearsThey all have their strengths and weaknesses, it really depends on the source image. Some algorithms may look better for images with sharp contrast lines, others may work better for natural scenes.
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aglassman about 10 yearsJust do some google searching. There is a lot of blog posts and other things out there on which algorithms work best for which types of images. In the end though, it comes down to what looks better to you.
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Mark Ransom about 10 yearsThe problem is that while "bicubic" is a well defined algorithm, "antialias" is not. It's impossible to find a blog post which will define the difference. The algorithm used by PIL is probably well known, just not by that name. I've never tried to dig into the source to figure it out for myself though.
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princ_sameer over 6 yearsDid you report theses issues to PIL? and regardless do you happen to know if they are still issues?
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Mark Ransom over 6 years@GordonWrigley No and no. I suspect with active development on Pillow that things have improved.
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user666 over 5 yearsLooks like the
ANTIALIAS
filter has been renamed toLANCZOS
, and the release notes say it has been fixed. pillow.readthedocs.io/en/3.0.x/releasenotes/2.7.0.html -
Mark Ransom over 5 years@user666 that's good news! Thanks for the link to the release notes. They address every issue I found.