Ken, very good points and an interesting take on the subject.
I think however that you may be overestimating how good the kernels are at removing aliasing. I\'ll show some examples below but from what I\'ve seen to truly eliminate aliasing you need to be more aggressive in the low pass filtering than the regular bicubic algorithms are - including lanczos3. And to top it off, to get a crisp picture you need to add sharpening which to a varying extent undoes what the resampling kernel did in the way of removing aliasing. For instance a deconvolution sharpening can recover amazing (false) detail.
I\'ll aim to show:
1) That bicubic/lanczos3 does not remove aliasing
2) That sharpening undoes any anti-aliasing effect the down sampling algorithm had
3) That an unsharpened image looks less visually appealing than a sharpened one and that it closer resembles qualitatively the higher resolution original.
4) That to truly remove all aliasing you need to low-pass filter the image beyond what most people would consider acceptable
1) Bicubic/lanczos3 & aliasing.
We\'ll use the 16x16 -> 8x8 example here that contains two basic spatial frequencies plus a diagonal line.
As you can see in the 8x8 we can see aliasing. The contrast has dropped but it\'s still visible.
2) Sharpening undoes anti-aliasing:
Sharpening applied and any AA effect that the lanczos3 had is gone. So if we want to remove the aliasing, sharpening is verboten.
3 & 4) I\'ll start by posting a 100% crop so that you know what the texture looks like before resizing:
I\'ll show three examples here. Open them in separate tabs in your browser and flip between them.
The last image has been low pass filtered before resize to remove all spatial frequencies that cannot be represented in the resized image without aliasing.
Which do you think looks best and in which one is the texture qualitatively closest to the 100% crop? My answer is 2) without hesitation.
If you agree, what conclusions can be drawn? Well, you made a good point that it\'s not aliasing I like but rather that I dislike the brute nature of the anti aliasing process - even with a sophisticated kernel such as the lanczos3. In practice it makes no difference though when it comes to the processing. If you skip/counteract the anti aliasing, you end up with aliasing and if it looks better, well, that\'s it then.
Aug 16, 2011 at 05:01 PM
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