Digital BW, The Print

> From: tvalleau [mailto:tracy@...]
>
> AntiAliasing is a "cure" to color issues, and has nothing (much) to do
> with luma. The anti-aliasing filter may be physical (which can lend to
> softness issues that can be severe, and easily discernable,  or it
> calculated, which produces information depending on how well done the
> algorythms are, and the layout of the sensors.)
>
> The need for anti-aliasing comes from trying to deal with a
> sensor-group which has two different colors meeting in a sharp line
> across it.

Anti-aliasing most certainly does apply to luma. A monochrome sensor, or
true co-located RGB sensor like the Foveon chip, still needs anti-aliasing,
just at a higher spatial frequency than a Bayer chip. It's certainly more
important for a Bayer chip, because color aliasing is uglier than simple
luma aliasing, but you most definitely can get aliasing (moire) in
monochrome images. The Sigma camera doesn't include an anti-alias filter,
which makes its images extremely sharp, but also produces jaggies and moire
on some images.

Also, anti-aliasing _must_ be done with a diffuser over the sensor, and
can't be done after the fact through calculation. Once the image is
spatially sampled by the sensor layout pattern, it's too late to fix
aliasing.

> Take a camera RAW of 6 megs, and blend the three layers to your liking
> for full tonal range, and you'll have a perfectly sharp 6 meg photo.

What if the image has detail only in the red or blue channel? Consider the
case of some tree branches against blue water, or some telephone wires
against a red wall. In that case, virtually all the detail is in one
channel, and adding the other two does nothing.

Your other points I basically agree with.

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Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@...