White paper: Foveon 2.4 - 5.0 times higher resolution than same MP Bayer

http://foveon.com/docs/Frequency.pdf

Well validated in these Sigma SD9 vs Canon 1Ds tests...
http://www.outbackphoto.com/artofraw/raw_05/essay.html

That means the $650 Simga SD9 and $1000 SD10 =
8.3MP Bayer camera for B&W targets
17.1MP Bayer camera for full color targets

 

I like the idea of the operation of the chip, but test show that the color
fades at the higher ISO setting above 200.
Give it time to mature.
I need full color, LOW Noise, at the 1600 ISO setting.

 

It took you a long time to find that document...

Its conclusions are biased, and misleading. They compare pixel resolution
while avoiding to mention the number of discretely sampled output pixels.
According to their reasoning, a camera with one pixel is better than one
with 6MP, obviously ludicrous.

That 'comparison' was specifically construed to "exploit" certain feature
differences and "fool" the Canon sensor. The carefully chosen worst-case
color combination, is also extremely unlikely to be encountered in a normal
scene.

Again you are carefully avoiding to mention the difference in using a
low-pass filter on the Canon and the lack of a low-pass filter on the Sigma,
leading to aliasing artifacts with the Sigma.
Also avoiding the fact that the low fill factor of the sensors in the Sigma
leads to a further need for such a low-pass filter to avoid aliasing and
stair-stepping.
Also avoiding to point out that the Field of View between cameras was
different, <http://www.xs4all.nl/~bvdwolf/main/downloads/AoR.png> because a
fair test would have given something closer to this result:
http://www.xs4all.nl/~bvdwolf/main/downloads/SD-9_identical_FoV_to_1Ds.jpg

And for a more meaningful resolution comparison, compare:
http://www.dpreview.com/reviews/orig.asp?/reviews/samples/rescharts/sigma_sd9.jpg
which
starts to misrepresent the finer lines above the 12 marker (even counts only
4 or 5 black
lines at the 20 marker instead of 9), with:
http://www.dpreview.com/reviews/samples/rescharts/canon_eos1ds.jpg which has
little trouble
resolving the finest detail at the 20 marker (we need more detailed test
cards for this
camera), and the Fuji S2 at 12MP output setting on the same page
http://www.dpreview.com/reviews/canoneos1ds/page21.asp also reaches a
reasonable 18+ mark.

Bart

 

Typical preddy bullcrap.

 

Interesting tests. At least they matched the field of view of the
cameras, which the outbackphoto test failed to do.

The main thing the resolution tests show is the lack of an anti-aliasing
filter. They show considerable contrast above the Nyquist frequency for
the X3, which is BAD because it causes aliasing. The 10D's contrast
drops much lower at the Nyquist frequency because of the presence of the
AA filter, which is necessary. This also reduces contrast below
Nyquist, but that can be restored by a bit of sharpening.

You can see the unpleasant side effects of no AA filtering in the
diagonal line test shown in Figure 7. The Canon slanted line looks like
it is the same width everywhere with smooth edges. The Sigma SD10 image
of the same line looks like the edge of the line is wavy and the
width of the line varies. (And the SD9 would have been worse yet!).

Is there anyone other than George who would prefer the wavy line on the
right to the clean line on the left, particularly when a bit of
sharpening will eliminate most of the sharpness difference while nothing
will fix the waviness of the line on the right?

Also, they are quoting resolution in cycles/pixel terms, not cycles per
image height. What the data says is that the X3 sensor has higher
contrast and thus higher apparent sharpness with the same number of
pixels. Unfortunately for Sigma/Foveon, no other current DSLR does have
as few pixels as the SD9/SD10, and so the comparison is not accurate.

To compare the 10D to the SD10 on a lines per picture height basis, the
data for the 10D would have to be stretched horizontally by a factor of
1.4 relative to the SD10, giving about the same contrast at lower
frequencies and considerably higher useful resolution. To compare the
11 MP 1Ds, the Canon graph would have to be stretched horizontally by a
factor of nearly 2. It would then beat the SD10 at all frequencies even
without any sharpening.

In other words, the paper pretty clearly demonstrates that a Foveon
sensor without an anti-aliasing filter is badly flawed for photography.

Those have been discredited many times in this newsgroup.

Finally, note that George seems to be misinterpreting the test results.
When the paper says "the frequency response of the Foveon is 2.4X that
of the Bayer", what they mean is that the amplitude (contrast) is
higher at a particular frequency. They do *not* mean that the upper
frequency cutoff (the more usual meaning of frequency response) is any
higher for the Sigma. That's set by the Nyquist limit, and the Sigma is
worse than all other DSLRs in this respect because it just has fewer
sensing sites than anything else.

Nothing in the paper quoted supports George's math above.

Dave

 

Only if color sampling is taking place, which with Foveon it never
does, it is a full color sensor. That is why there is never color
aliasing in Foveon shots, in fact color moire is absolutely
impossible.

By two grade schoolers. Those tests simply show raw data. The fact
that you are offended by raw data is proof that you are acting
irrationally.

"The results show that the SFR for Foveon X3 sensors is up to 2.4x
better. In
addition to the standard SFR method, we also applied the SFR method
using a red/blue edge. In this case, the X3 SFR was 3–5x higher than
that for Bayer filter pattern devices."

Obviously B&W targets are meaningless, color targets count. The 2.4X
figure (derrived from B&W targets, when no color interpolation is
required) is always cited, and it is ridiculously conservative in
favor of Bayer.

Bayer is great for black, but black only because any sensor, R, G, or
B can return a black reading. IOWs, as long as there is no light, you
get the Bayer-advertised MP rating. If there is light, you're out of
luck to the tune of a 75% drop in optical resolution. Though this
papers claims 80%, probably due to the additional effect of the
Foveon-unecessary blur filter.

 

In message <>,

The Sigma resolution images are aliased. The 10D ones look better, IMO.

They didn't mention that frequencies near-but-below the nyquist on the
10D are attenuated, but respond to sharpening very well.
--

 

All cameras sample color.

Of course there is.

Yeah, that's about all it would take to discredit your bullshit.

 

The problem with the Sigma camera is that there is lots of luminance
aliasing. Look at the diagonal line in the paper you referenced: it
looks like it has a scalloped edge and isn't uniform in width.

The reason is that anti-alias filtering is needed in all systems that
regularly sample a continuous function at discrete points. This is
perhaps the most fundamental basis of digital signal and image
processing. It applies to digital audio, to black&white cameras, and to
colour cameras. This includes the ones with the Foveon sensor; to say
otherwise is simply preposterous.

The contrast graphs clearly mark where the Nyquist frequency is, and the
Foveon-sensor camera clearly has quite high contrast at the Nyquist
frequency. Any student who has taken one signal processing class can
tell you that the result will be aliasing.

What the tests show is that if you make test images using
complementary-colour test targets designed to show Bayer sensors at
their weakest, and shoot under conditions of unequal fields of view that
discard all the extra pixels of the other DSLRs, the Sigma cameras can
sort of equal other DSLRs. Those results are valid on their own, once
you understand the test questions.

However, you tend to quote that page as if it showed superiority for the
Sigmas (it doesn't), and as if it was related to normal photographic
subjects (it's not). Further, you normally just post pointers to the
two images, without the explanation. It's *your* use of that page to
support your argument that has been discredited.

And what does that value of "2.4X" mean? If one reads the paper
(you obviously did not read it, or did not understand it), that value is
a contrast difference at a single spatial frequency. What it says is
that if you shoot a picket fence at a particular distance with the SD10,
and then recompose the shot so the same area fills the same number of
pixels on the 10D (i.e. discarding half of its sensor area), then the
raw data from the Foveon sensor will show more contrast than the raw
data from the 10D. It absolutely does not indicate that the SD10 has
any higher resolution - this is a measurment *at the same resolution per
pixel on both cameras*, and it pretends that the higher pixel count of
the 10D does not matter.

But, in fact, the 10D does have more pixels, and does have a higher
resolution as well, as clearly demonstrated by dpreview's resolution
tests. And the high contrast of the SD10 at the Nyquist frequency,
clearly visible on the graphs, mean that it's not suitable for general
photography at all.

There is absolutely no way that, if a camera has 2X as much contrast at
a particular frequency, that you can say it is equivalent to one with 2X
as many pixels. As the robot on a particular TV program used to say,
"That does not compute".

But that number tells you nothing at all about resolution - it's a
contrast measurement. Read the paper! And B&W targets *do* count,
because the human eye has 10 times higher resolution for seeing
luminance changes than colour changes. That's why most camera testing
uses B&W charts.

That's not an argument; it's just babbling.

Dave

 

Nonsense. Aliasing can even take place in a 'monochrome' sensor. Color is
totally irrelevant.

SNIP

No, not in resolution, which is your claim.

Which proves that you don't understand what they have written.

A higher SFR means a higher modulation, and I may add at a frequency that
seems to be carefully picked to maximize the difference with properly
anti-aliased images.

Yet many of the SFR tests described by the paper were done with a black and
white slanted edge target. So you mean to say that those tests they
performed were wrong?????

SNIP of more misunderstood results.

No they don't. They always carry a signal, because true black only exists in
a theoretical Blackbody, and there is always noise. Black only exists after
subtracting a certain Blackpoint level.

SNIP of more misinformation and Preddy weird science.

Even a reflective Black and White target on a Photographic silver image with
the highest dynamic range will still reflect 0.5% of the incident light.
That 0.5% is only 7.7 bits darker than Saturated White, and paper White is
only 95% reflection, so the difference is even easier to catch than that.
The conclusions you draw, are therefore completely baseless.

What is more, the SFR tests do not allow to saturate the sensor, nor do they
allow a blacklevel that leads to zero luminance, so a lower contrast target
should be used.

Bart