In praise of AA filters

Started 9 months ago | Discussions thread
crames
Regular MemberPosts: 192
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Wait a minute: Foveon example not so aliased after all...
In reply to Lee Jay, 9 months ago

Lee Jay wrote:

Basalite wrote:

hjulenissen wrote:

Basalite wrote:

it needs to be emphasized that the Foveon sensors in Sigma's cameras do not need nor do they have such a filter

It needs to be emphasised that aliasing occurs for any sampling that is fed signal energy beyond the Nyquist frequency (after pre-filtering). This is true for Foveon-type as well as achromatic sensors.

Computer games are not rendered through a Bayer CFA. Still, anti-aliasing techniques are quite popular.

As is true with many people in this forum that seem to be more concerned with displaying their technical knowledge, you're missing the forest for the trees. Foveon sensors simply do not have the image degrading qualities that Bayer sensors have, and that is the motivation for installing a *blur* filter.

Wikipedia: Foveon X3 sensor

"Because demosaicing is not required for the Foveon X3 sensor to produce a full-color image, the color artifacts ("colored jaggies") associated with that process are not seen. The separate anti-aliasing filter commonly used to mitigate those artifacts in a Bayer sensor is not required. This is because little aliasing occurs when the photodiodes for each color, with the assistance of the microlenses, integrate the optical image over a region almost as big as the spacing of sensors for that color."

Thanks for the example. That X3 image is covered with aliasing artifacts. It may lack most color moire but it's full of luminance moire. The lack of an AA filter is one reason of many I've never seriously considered a Sigma camera and the example above shows why.

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Lee Jay
(see profile for equipment)

Take a look at the foveon example zoomed 300% with sinc interpolation. There is actually only a few small aliased patches, mostly in the upper left.

Foveon zoomed 300% with sinc interpolation

You can't really evaluate aliasing without doing some interpolation - has to do with the sampling theorem. If it goes away when you interpolate, it can't be aliasing.

What people often think is aliasing is really caused by the way the image is displayed, rather than the way it is captured.

Cliff

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