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Michael Reichmann reasoning for AA filters?

 
 
W
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      10-19-2007
Okay, does this make any sense: http://www.luminous-landscape.com/essays/MKIIIs.shtml

M. Reichmann says that DSLRs have AA filters to save compute power
needed in demoscaicing Bayer pattern sensors whereas medium format
backs do not have AA filters because they do not need to demosaic and
create jpgs in the camera.

Sampling theory says that ANY sampled data system requires an AA
filter to keep higher (spatial) frequencies from aliasing into lower
(spatial) frequencies. I do not understand Reichmann's assertion. It
seems to igore the basics of sampled data system theory.

Any comments?

 
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nospam
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      10-19-2007
In article <(E-Mail Removed) .com>,
<(E-Mail Removed)> wrote:

> Okay, does this make any sense:
> http://www.luminous-landscape.com/essays/MKIIIs.shtml
>
> M. Reichmann says that DSLRs have AA filters to save compute power
> needed in demoscaicing Bayer pattern sensors whereas medium format
> backs do not have AA filters because they do not need to demosaic and
> create jpgs in the camera.


from that page:

They have an AA filter primarily to save battery power and processing
time when computing a JPG.

that is absolutely ludicrous.

> Sampling theory says that ANY sampled data system requires an AA
> filter to keep higher (spatial) frequencies from aliasing into lower
> (spatial) frequencies. I do not understand Reichmann's assertion. It
> seems to igore the basics of sampled data system theory.


that's correct.
 
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David J Taylor
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      10-19-2007
W wrote:
> Okay, does this make any sense:
> http://www.luminous-landscape.com/essays/MKIIIs.shtml
>
> M. Reichmann says that DSLRs have AA filters to save compute power
> needed in demoscaicing Bayer pattern sensors whereas medium format
> backs do not have AA filters because they do not need to demosaic and
> create jpgs in the camera.
>
> Sampling theory says that ANY sampled data system requires an AA
> filter to keep higher (spatial) frequencies from aliasing into lower
> (spatial) frequencies. I do not understand Reichmann's assertion. It
> seems to igore the basics of sampled data system theory.
>
> Any comments?


I agree with you. However, the actual AA filter characteristics differ
between audio and digital cameras. In audio, brick-wall characteristics
are the aim, whereas in photography certain cameras (Sigma, in particular)
have a very weak AA filter, or even omit it, "as the results look
sharper"! Guess which I won't be buying!

David


 
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Annika1980
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      10-19-2007
On Oct 18, 10:57 pm, W <(E-Mail Removed)> wrote:
> Okay, does this make any sense:http://www.luminous-landscape.com/essays/MKIIIs.shtml
>
> Sampling theory says that ANY sampled data system requires an AA
> filter to keep higher (spatial) frequencies from aliasing into lower
> (spatial) frequencies. I do not understand Reichmann's assertion. It
> seems to igore the basics of sampled data system theory.
>
> Any comments?


His site has been updated:

Postscript
In a version of this review which was online for a few hours on Oct
18-19, there was a discussion of antialiasing filters and how I felt
that there would be advantages to the 1Ds MKIII not having one, for a
variety of reasons. Due to a mix-up, an early version which was not
intended for publication because of mistakes in my initial analysis,
found its way online in error.

I regret any confusion that this may have caused.



 
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W
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      10-19-2007
Wow, he completely removed the whole discussion no AA filters.

While I understand the need for AA filters (my earlier post). I must
admit, I do not understand why the medium format digital backs do not
include an AA filter. Aside from moire issues, I would think that any
kind of periodic image elements (e.g. a fence) could cause problems if
there were no AA filter.


On Oct 19, 7:00 am, Annika1980 <(E-Mail Removed)> wrote:
> On Oct 18, 10:57 pm, W <(E-Mail Removed)> wrote:
>
> > Okay, does this make any sense:http://www.luminous-landscape.com/essays/MKIIIs.shtml

>
> > Sampling theory says that ANY sampled data system requires an AA
> > filter to keep higher (spatial) frequencies from aliasing into lower
> > (spatial) frequencies. I do not understand Reichmann's assertion. It
> > seems to igore the basics of sampled data system theory.

>
> > Any comments?

>
> His site has been updated:
>
> Postscript
> In a version of this review which was online for a few hours on Oct
> 18-19, there was a discussion of antialiasing filters and how I felt
> that there would be advantages to the 1Ds MKIII not having one, for a
> variety of reasons. Due to a mix-up, an early version which was not
> intended for publication because of mistakes in my initial analysis,
> found its way online in error.
>
> I regret any confusion that this may have caused.



 
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David J. Littleboy
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      10-19-2007

"W" <(E-Mail Removed)> wrote:
> Wow, he completely removed the whole discussion no AA filters.


Somebody he trusts must have clued him in on how far off he was.

> While I understand the need for AA filters (my earlier post). I must
> admit, I do not understand why the medium format digital backs do not
> include an AA filter.


Bad design<g>? The last time I spent some time lurking on an MF digital
list, they were just begining to figure out what a disaster it is. If you
have any fabrics in the scene, many of your images will be unusable. It's
simply not acceptable for professional work, or any other context in which
failure isn't acceptable. Going for extra sharpness by leaving out the AA
filter is amateur in the extreme.

> Aside from moire issues, I would think that any
> kind of periodic image elements (e.g. a fence) could cause problems if
> there were no AA filter.


You mean like this? (100% crop from 5D, whose AA filter is a tad on the
inadequate side. Sigh.)

http://www.pbase.com/davidjl/image/52118414/original

David J. Littleboy
Tokyo, Japan


 
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David J Taylor
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      10-19-2007
W wrote:
> Wow, he completely removed the whole discussion no AA filters.
>
> While I understand the need for AA filters (my earlier post). I must
> admit, I do not understand why the medium format digital backs do not
> include an AA filter. Aside from moire issues, I would think that any
> kind of periodic image elements (e.g. a fence) could cause problems if
> there were no AA filter.


Maybe the lenses used aren't good enough to need AA filters? Too small an
MTF at half the sampling frequency?

David


 
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W
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      10-19-2007
Wow yes, great example with the 5D. I have even seen moire with my
20D with fabrics.

Regarding the MF digital backs, I can't believe that the folks
designing MF sensors are that "stupid". I still don't get it.

On Oct 19, 9:55 am, "David J. Littleboy" <(E-Mail Removed)> wrote:
> "W" <(E-Mail Removed)> wrote:
> > Wow, he completely removed the whole discussion no AA filters.

>
> Somebody he trusts must have clued him in on how far off he was.
>
> > While I understand the need for AA filters (my earlier post). I must
> > admit, I do not understand why the medium format digital backs do not
> > include an AA filter.

>
> Bad design<g>? The last time I spent some time lurking on an MF digital
> list, they were just begining to figure out what a disaster it is. If you
> have any fabrics in the scene, many of your images will be unusable. It's
> simply not acceptable for professional work, or any other context in which
> failure isn't acceptable. Going for extra sharpness by leaving out the AA
> filter is amateur in the extreme.
>
> > Aside from moire issues, I would think that any
> > kind of periodic image elements (e.g. a fence) could cause problems if
> > there were no AA filter.

>
> You mean like this? (100% crop from 5D, whose AA filter is a tad on the
> inadequate side. Sigh.)
>
> http://www.pbase.com/davidjl/image/52118414/original
>
> David J. Littleboy
> Tokyo, Japan



 
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Paul Furman
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      10-19-2007
David J Taylor wrote:
> W wrote:
>
>>Wow, he completely removed the whole discussion no AA filters.
>>
>>While I understand the need for AA filters (my earlier post). I must
>>admit, I do not understand why the medium format digital backs do not
>>include an AA filter. Aside from moire issues, I would think that any
>>kind of periodic image elements (e.g. a fence) could cause problems if
>>there were no AA filter.

>
> Maybe the lenses used aren't good enough to need AA filters? Too small an
> MTF at half the sampling frequency?


My guess is these users want extreme detail and I assume there are
fairly easy ways to process moire patterns out in post. It's more work
but that kind of photography is not for fast turnover.

--
Paul Furman Photography
http://edgehill.net
Bay Natives Nursery
http://www.baynatives.com
 
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Doug McDonald
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      10-19-2007

>
>>> Aside from moire issues, I would think that any
>>> kind of periodic image elements (e.g. a fence) could cause problems if
>>> there were no AA filter.

>> You mean like this? (100% crop from 5D, whose AA filter is a tad on the
>> inadequate side. Sigh.)
>>
>> http://www.pbase.com/davidjl/image/52118414/original
>>
>> David J. Littleboy
>> Tokyo, Japan

>
>


For a photo like that, meaning everything can be in focus,
there is always God's AA filter: diffraction.

Doug McDonald
 
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