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Anti-aliasing, Color Separation, etc.

 
 
David J. Littleboy
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      12-19-2003

"pehache" <(E-Mail Removed)> wrote:
>
> In a Bayer sensor without AA filter,


There's never a Bayer sensor without an AA filter. (Except for Kodak 14n and
some of the MF digital backs, and the 14n exhibits nasty artifacts.)

> In the Foveon sensor without AA filter, the luminance and chrominance
> components are slightly aliased.


There's also never a Foveon sensor without an AA filter. At least not on my
shelf there isn't.

> As a consequence, a Bayer-based sensor should have an aggressive
> AA-filter to completely dealiase the chrominance componants (at the
> expense of an unecessary blurring of the luminance component), and a
> Foveon sensor should have a light AA-filter to dealiase all its
> components.


The Foveon AA filter must completely, 100%, totally, attenuate all
frequencies at and above Nyquist.

Any practical AA filter that does that will, I suspect, be adequate for a
Bayer sensor. If not, it will be very close to adequate.

> Saying that the Foveon does not require AA-filter is false, or at
> least a strong shortcut. But what is true is that the Foveon requires
> less AA-filtering than Bayer's


That _may_ be true. (See my other note.*)

Seriously investigating what
the practical effects of that difference would be is an interesting
question. But that's not what Foveon is doing, so it's irrelevant to the
cameras we have as options. The better Bayer cameras are quite good at
minimizing artifacts, so as a practical issue were faced with fairly
reasonable camera implementations on the one hand and an incorrect
implementation on the other.

David J. Littleboy
Tokyo, Japan

*: Here's what I said.
>>>>>>

FWIW, if the SD9 and SD10 cameras had anti-aliasing filters, and if Foveon
was arguing that Bayer cameras required a stronger AA filter and that the
Foveon sensor could deliver, say 66% of the Nyquist frequency whereas Bayer
cameras could only deliver 55% without objectionable artifacts, and that
Foveon therefore delivered 66/55 or 20% better resolution than (or 1.44
times as many megapixles as) Bayer sensors, I'd be on the Foveon side of the
fence. But that's not what they're saying. (These numbers are guesses. It's
probably more like 66% vs. 60%.)
<<<<<<<<



 
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JPS@no.komm
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      12-19-2003
In message <bru9ro$tst$(E-Mail Removed)>,
"David J. Littleboy" <(E-Mail Removed)> wrote:

>I've got fewer posts in these threads than just about anyone else here<g>.
>
>FWIW, if the SD9 and SD10 cameras had anti-aliasing filters, and if Foveon
>was arguing that Bayer cameras required a stronger AA filter and that the
>Foveon sensor could deliver, say 66% of the Nyquist frequency whereas Bayer
>cameras could only deliver 55% without objectionable artifacts, and that
>Foveon therefore delivered 66/55 or 20% better resolution than (or 1.44
>times as many megapixles as) Bayer sensors, I'd be on the Foveon side of the
>fence. But that's not what they're saying. (These numbers are guesses. It's
>probably more like 66% vs. 60%.)


The SD9 records at least 2 or 3 times the nyquist upon capture, but of
course, it's all below the nyquist in the output file, and 125% of the
nyquist becomes 75% of the nyquist, 190% of the nyquist becomes 10% of
the nyquist, 300% the nyquist becomes the nyquist, etc, etc. There are
no microlenses and the photosites only cover 30% of the sensor surface.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <(E-Mail Removed)>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><

 
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JPS@no.komm
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      12-19-2003
In message <(E-Mail Removed) >,
http://www.velocityreviews.com/forums/(E-Mail Removed) (pehache) wrote:

>But what is true is that the Foveon requires
>less AA-filtering than Bayer's ("no" versus "light" is "less", as well
>as "light" versus strong is "less").


That would be very nice if they came in the resolutions that monochrome
sensors with CFAs came in.

I have my doubts that we will see practical full-RGB senesors for
high-res digicams anytime soon. As long as you can get more spatial
witnesses with CFAs, you will get better luminance resolution with them.
These sensors we're discussing are *far* from exausting the detail
delivered by the sharpest lenses available. I can put a Canon 1.4x TC
*AND* a Tamron 2x SP on my 300mm F4L IS lens, and it still delivers 84%
the resolution of the lens by itself, as limited by the 10D's sensor.
That means that the lens has at least 2.37x the resolution that the 10D
sensor can handle, and probably almost 4x as much as the SD9's csensor
can, if you could mount it on one. And that lens is a toy, compared to
the f2.8 version.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <(E-Mail Removed)>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><

 
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Rodney Myrvaagnes
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      12-19-2003
On Fri, 19 Dec 2003 06:36:12 GMT, "Paul H." <(E-Mail Removed)>
wrote:

>
>"David J. Littleboy" <(E-Mail Removed)> wrote in message
>news:brthpj$mmd$(E-Mail Removed)...
>
>
><< snip>>
>> Sleazy advertising is not a trifle.

>
>>
>> David J. Littleboy
>> Tokyo, Japan

>
>Simply put, you're a zealot with an undue penchant for hyperbole. I'd hardy
>call the the so-called advertising you mention "sleazy", a word more
>appropriately used to describe the practice of selling child pornography,
>not the marketing of digital cameras.


David Littleboy is one of two or three regular contibutors of actual
technical information to this news group. I have learned a lot from
his posts.

"Sleazy" is a reasonable word for the stealthy presentation of
misleading marketing hype in the guise of neutral background.

>Get real.


Yes.
> Secondly, I have no
>personal stake in the matter, but simply wanted to point beginners to a page
>giving out simple definitions for phenomena such as aliasing. I happened to
>point them to one of my many bookmarks, a site which I still contend is
>useful if one sticks to technical matters and ignores opinion.


The site is so organized that a beginner wouldn't be able to do that,
as apparently you also are not. I took it at face value until I
noticed the grossly impossible color-response graph for stacked
sensors and the absence of a "Disadvantages" list for the stacked
sensor.



> You, on the
>other hand, gave out nothing but venom when you could have instead directed
>people to a site or sites you thought more appropriate and/or brand-neutral.
>Thanks for furthering understanding and yet again hijacking another message
>thread to I-hate-Foveon Land.
>
>You have an Ahab-like fixation on the Foveon sensor that's nearly
>unbelievable; I can even imagine your bedroom littered with slashed
>matresses and torn-open pillows, the sorry renmants of a search undertaken
>because you thought you heard a Foveon whispering evil things whenever the
>lights were out. Get a grip.
>



Rodney Myrvaagnes J36 Gjo/a


"In this house we _obey_ the laws of thermodynamics." --Homer Simpson
 
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Paul H.
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      12-19-2003

"David J. Littleboy" <(E-Mail Removed)> wrote in message
news:bru9ro$tst$(E-Mail Removed)...
>

<< snip >>
>
> http://web.mit.edu/2.161/www/Handouts/digital.pdf
>
> I doubt that you'll be happy with that, but it's quite a good page. The

last
> time I went looking, I was looking in the Electrical Engineering

department
> (which is where this stuff was taught in the mid-70s) and didn't find it.


I'm perfectly happy with stuff like this (I have degree in physics and years
ago even coded discrete transforms in assembly language) but I was trying to
find something understandable by and useful to people who have somewhat less
than a nodding acquaintance with concepts like the delta function and
distrubution theory. Most people, believe or not, have had very little
exposure to either discrete (or continuous) Fourier transforms and yet would
like to acquire a workman-like/intuitive understanding of concepts such as
aliasing, as well as other technical matters critical to making a decision
to purchase a high-quality camera. An intelligent person can, for example,
understand refraction without being able to state Snell's Law.

But thanks for the link.

>
> Normal Koren's site has a wealth of good stuff. I've pointed a lot of

people
> to it. But I don't think it has anything on aliasing. (I think it simply
> assumes that the cameras of concern are implemented correctly.)
>
> http://www.normankoren.com/
>
> > You have an Ahab-like fixation on the Foveon sensor that's nearly
> > unbelievable; I can even imagine your bedroom littered with slashed
> > matresses and torn-open pillows, the sorry renmants of a search

undertaken
> > because you thought you heard a Foveon whispering evil things whenever

the
> > lights were out.

>
> I've got fewer posts in these threads than just about anyone else here<g>.
>
> FWIW, if the SD9 and SD10 cameras had anti-aliasing filters, and if Foveon
> was arguing that Bayer cameras required a stronger AA filter and that the
> Foveon sensor could deliver, say 66% of the Nyquist frequency whereas

Bayer
> cameras could only deliver 55% without objectionable artifacts, and that
> Foveon therefore delivered 66/55 or 20% better resolution than (or 1.44
> times as many megapixles as) Bayer sensors, I'd be on the Foveon side of

the
> fence. But that's not what they're saying. (These numbers are guesses.

It's
> probably more like 66% vs. 60%.)


Well, sorry about the Ahab comment, but no one likes being termed a stooge
for anyone else's point of view, even by implication. I don't necessarily
disagree with many of the more rational complaints about the Foveon
approach, but I am tired of, and sensitive to, the intimations that somehow
Foveon was started solely to produce and market worthless crap, and that any
engineer who ever associated himself with Foveon (or Sigma) is somehow
tainted so badly his statements can never be trusted again.




 
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Paul H.
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      12-19-2003

"Rodney Myrvaagnes" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Fri, 19 Dec 2003 06:36:12 GMT, "Paul H." <(E-Mail Removed)>
> wrote:


<<snip>>
> The site is so organized that a beginner wouldn't be able to do that,
> as apparently you also are not.


<Sigh> Now, now...

> I took it at face value until I
> noticed the grossly impossible color-response graph for stacked
> sensors and the absence of a "Disadvantages" list for the stacked
> sensor.


Grossly impossible? Grossly over-simplified, perhaps, but no more so than
was the related graph for the Bayer-type sensor; I simply thought the graphs
were intended to be schematic and illustrative rather than truly
mathematical in nature. I must admit, though, I had overlooked the lack of
a "disadvantage" list for stacked sensors and that is a real oversight by
the author. However, after re-reading the page I still don't see the
extreme bias to which others have referred: Indeed, even the conclusion
comparing stacked sensors to Bayer-type sensors was fairly bland; at no
point did the author ever say anything approaching "therefore, stacked
sensors are far superior." Thus while "bias" may be present, I don't see
real advocacy and I still think the phenomenon of spatial aliasing was
illustrated effectively.

What I don't understand, however, is the extreme dislike of Foveon/Sigma
exhibited by many on this newsgroup: after all, Foveon sensors represent a
mere blip in the digital camera marketplace and, to me, at least seem more
of an interesting technical curiosity than a threat to the future of digital
cameras. However, what I was trying to do was NOT contribute to the
controversy, so if I can find some other elementary and far less
controversial sites, I'll post the url's, then put my shields up.



 
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eawckyegcy@yahoo.com
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      12-19-2003
"Paul H." <(E-Mail Removed)> wrote:

> I don't own a Foveon-based camera, I don't plan to own a Foveon-based
> camera, all of my cameras are based upon the Bayer-filtered sensor, and my
> next camera, the Canon 300D, will be a Bayer-type camera. Nevertheless, I
> found the information presented on the site to be factual, fairly unbiased
> and I still contend the page can serve as a good introduction to some of the
> topics currently under discussion in this newsgroup.


It is a thinly disguised Foveon advertisement. Wasn't it obvious?

> I assumed, of course,
> a certain intelligence on the part of the reader which would lead him or her
> to seek out other sources for futher information, if desired.


Then you assume intelligence that you yourself have not evidenced.

> But more to
> the point, you could have used your own post to direct beginners (the
> non-illuminati) to better, less-biased (in your opinion) sources of
> accessible technical information, but you did not; instead, you chose to
> quibble and insinuate. And that, my friend, is the real problem with
> rec.photo.digital these days.


I could have solved a nasty differential equation too, "but I did
not". What is the point of your distraction here? Right: that
_your_ reference is nothing more than a warmed over Foveon ad and you
didn't pick up on it. I am now obligated to fix your mistake? Get
real, dude.

> As to the author's Foveon associations, well, if Adolf Hitler himself once
> said the sun rose in the east, the character of the claimant didn't make the
> observation any less true. Maybe you need to stop seeking hidden agendas in
> trivialities.


Maybe you need to find your brain; you have apparently lost it.

> Finally, I did not mean this thread to turn into another I-hate/love-Foveon
> travesty of debate, but you, having taken that road, impel me to make a
> comment:


Nasty reading comprehension problem you have: I said absolutely
nothing at all good or bad about Foveon in my response to you.
 
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Paul H.
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      12-19-2003

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
<snip>

<pointless diatribe deleted>


> Nasty reading comprehension problem you have: I said absolutely
> nothing at all good or bad about Foveon in my response to you.



And what a nasty attitude _you_ have. Here's a quote from your original
response to me:

>But what is the "article" is a submarine-propaganda piece written by a
>Foveon dude?


> "note by Dick Merrill (Foveon)"


I hardly think the phrase "submarine-proganda piece" is a neutral comment
regarding Foveon, but perhaps your "writing comprehension" needs some work.

However, flame me if it pleases you, but where is your link to a site
containing elementary technical information? You don't provide one and the
tenor of your posting strongly suggests you're far more interested in a
meaningless fight than in discussing technical matters.



 
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Larry Lynch
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Posts: n/a
 
      12-19-2003
In article <7lIEb.10990$Pg1.1299
@newsread1.news.pas.earthlink.net>,
(E-Mail Removed) says...
> What I don't understand, however, is the extreme dislike of Foveon/Sigma
> exhibited by many on this newsgroup: after all, Foveon sensors represent a
> mere blip in the digital camera marketplace and, to me, at least seem more
> of an interesting technical curiosity than a threat to the future of digital
> cameras. However, what I was trying to do was NOT contribute to the
> controversy, so if I can find some other elementary and far less
> controversial sites, I'll post the url's, then put my shields up.
>



I dont think anybody here "HATES" the Foveon chip.. It
seems to be an experiment with merit.

What we "HATE" here are idiot zealot(s) (not speaking of
you here just the idiot(s)) who repeat marketing hype,
and outright LIES in the guise of information that might
lead a newbie down the path to purchase a camera that is
"NOT READY FOR PRIME TIME" and may NEVER be ready.

The Foveon is an experiment, and a damn fine one, which,
with a little work in the right direction MIGHT be a
leap forward in digital cameras.

Sadly, so far that leap has NOT taken place, and the
work doesn't seem to be happening, and the Sigma cameras
JUST DONT MAKE GOOD PICTURES.

We have seen a plethora of posts from certain people
over and over again praising this not ready for prime
time sensor/camera combo, so we get TESTY about it.
--
Larry Lynch
Lasting Imagery
Mystic, Ct.
 
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Rodney Myrvaagnes
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      12-20-2003
On Fri, 19 Dec 2003 18:48:14 GMT, "Paul H." <(E-Mail Removed)>
wrote:

>> Foveon therefore delivered 66/55 or 20% better resolution than (or 1.44
>> times as many megapixles as) Bayer sensors, I'd be on the Foveon side of

>the
>> fence. But that's not what they're saying. (These numbers are guesses.

>It's
>> probably more like 66% vs. 60%.)

>
>Well, sorry about the Ahab comment, but no one likes being termed a stooge
>for anyone else's point of view, even by implication. I don't necessarily
>disagree with many of the more rational complaints about the Foveon
>approach, but I am tired of, and sensitive to, the intimations that somehow
>Foveon was started solely to produce and market worthless crap, and that any
>engineer who ever associated himself with Foveon (or Sigma) is somehow
>tainted so badly his statements can never be trusted again.



I spent 16 years covering the semiconductor industry for an engineer's
trade magazine. I have listened to many intelligent technical people
talk pure hype when they are put in a marketing situation.

I have also seen them become honest engineers again afterward.

Sliding past the disadvantages of whatever you are selling is standard
practice. What elevated that web site into the 'sleaze' category was
disguising its marketing origin and pretending to be an overview.

If I had received that web file as an article proposal, my first
reaction woud have been "We want it, but it needs work."

It would have gone back to the author with such comments as "You left
off the disadvantages of the stacked sensor approach." Surely there
are some.

Second, I would have suggested that graphs of color sensitivity should
reflect actual silicon behaviour, rather than a fantasy. Since I would
have been busy on other things, I would probably have accepted the
article if he fixed those problems.

But, I might also have found time to read it more closely, and found
other problems. The easily-spotted gaps in the first submission woud
put the BS meter on high alert.


If the article were accepted, the author identfication would include
his position in the marketing dept. of the company.



Rodney Myrvaagnes J36 Gjo/a


"In this house we _obey_ the laws of thermodynamics." --Homer Simpson
 
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