[genotypewriter]

[quote name='Brightcolours' timestamp='1285243739' post='3157']

The AA filter will only add to the softening already there, it will not "mask" it.

[/quote]

I don't think things add up like that. Which ever is causing the more blur will be the one that's causing all the blur. An AA-filter tries to create a blur around roughly every 3 photosites and so you can think of this as a blur the size of 3 photosites. If the blur from diffraction is less than the radius of 3 photosites, you won't see the diffraction. If the blur from diffraction is greater than the size of 3 photosizes, say 5 photosizes big, then you will only see a blur of 5 photosites big... not 5+3=8.





[quote name='Brightcolours' timestamp='1285243739' post='3157']

The diffraction softening that each pixel samples will be the same for both a Bayer CFA array sensor and a Foveon sensor. The Foveon pixels will never get more soft than the Bayer ones.

[/quote]

Umm again not sure if you should go there so easily. Diffraction limitation depends on the size of the photosites. But does that mean a 14MP Bayer sensor and a 14MP Foveon with equal sized photosites resolve the same detail (resolution)? The short answer is no.



All that aside, I've also heard people talk about diffraction occurring at the photosite-level on Foveon sensors because of the depth the light has to travel to reach the bottom most layer. So the bottom-most layer, red, will be getting less light than the rest and the top and (mainly) the middle layer will be contaminated with diffracted red light.



If anyone's wondering which side I'm on... I like Foveon for how it tries to work and for most of its results. But Bayer CFA tends to give the most usable output <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='' />



GTW

[Brightcolours]

[quote name='genotypewriter' timestamp='1285827097' post='3380']

I don't think things add up like that. Which ever is causing the more blur will be the one that's causing all the blur. An AA-filter tries to create a blur around roughly every 3 photosites and so you can think of this as a blur the size of 3 photosites. If the blur from diffraction is less than the radius of 3 photosites, you won't see the diffraction. If the blur from diffraction is greater than the size of 3 photosizes, say 5 photosizes big, then you will only see a blur of 5 photosites big... not 5+3=8.







Umm again not sure if you should go there so easily. Diffraction limitation depends on the size of the photosites. But does that mean a 14MP Bayer sensor and a 14MP Foveon with equal sized photosites resolve the same detail (resolution)? The short answer is no.



All that aside, I've also heard people talk about diffraction occurring at the photosite-level on Foveon sensors because of the depth the light has to travel to reach the bottom most layer. So the bottom-most layer, red, will be getting less light than the rest and the top and (mainly) the middle layer will be contaminated with diffracted red light.



If anyone's wondering which side I'm on... I like Foveon for how it tries to work and for most of its results. But Bayer CFA tends to give the most usable output <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='' />



GTW

[/quote]

Those people have really weird ideas. The recording of diffraction is basically recording light that should have been intended for neighbouring pixels. I do not see how getting less light in the red layer would mean light intended for that pixel would end up in neighbouring pixels!



I really fail to see how diffraction softening could happen on pixel level, they are using a wrong term to describe something different.



Point remains: The foveon sensors will not be affected worse by diffraction. Diffraction is ONLY in the projected image, and the AA-filter-less sampling willnot get a more soft picture than an AA-filtered one.



Which brings us back to the reason Sigma images are "sharper"... due to the refusal to use AA-filters. If you remove the AA-filter from a Bayer CFA sensor, you will get the same kind of sharpness. Liked by some, disliked by those in the know (that is why most camera manufacturers put AA-filters in front).



Did you know, by the way, that the AA-filters are very expensive to develop and produce? They cost about the same as the sensor itself costs.

[genotypewriter]

[quote name='Brightcolours' timestamp='1285847839' post='3390']

I really fail to see how diffraction softening could happen on pixel level, they are using a wrong term to describe something different.

[/quote]

Think of it as a single slit diffraction experiment... the slit ofcourse is the Foveon pixel opening at the front. Fitting 4800 pixels on a sensor 24mm wide means a pixel is theoretically 5000nm wide. However, Foveon sensors have a fill factor of around 40%. If we round it up to 50%, the width of the slit (pixel opening) is 2500nm wide. This is a bit wider than the longest visible red wavelengths (which are around [url="http://en.wikipedia.org/wiki/Visible_spectrum#Spectral_colors"]700nm[/url] but it's quite close. But I'm giving the benefit of the doubt to Sigma here though... they wouldn't announce the sensor if such a fundamental problem was there.







[quote name='Brightcolours' timestamp='1285847839' post='3390']

Point remains: The foveon sensors will not be affected worse by diffraction. Diffraction is ONLY in the projected image, and the AA-filter-less sampling willnot get a more soft picture than an AA-filtered one.

[/quote]

What is the meaning of soft? Is it when comparing a 14MP Bayer CFA image vs. a 14MP Foveon? You need to establish the pixel sizes first before talking about the effects of diffraction.





[quote name='Brightcolours' timestamp='1285847839' post='3390']

Which brings us back to the reason Sigma images are "sharper"... due to the refusal to use AA-filters. If you remove the AA-filter from a Bayer CFA sensor, you will get the same kind of sharpness. Liked by some, disliked by those in the know (that is why most camera manufacturers put AA-filters in front).

[/quote]

As a person who has a 50D without an AA-filter and lenses that can out-resolve a 50D without an AA-filter, I can say that this is not true. Plain removal of the AA-filter doesn't give the same resolution of a Foveon (again, what sizes are the compared sensors here?). In fact, from my experience, when the AA-filter of a Bayer CFA is properly matched to the pixel sizes of the sensor, that is when the produced images are more "Foveon-like". Removing the AA-filter only helps if it's overly strong, such as in the case of the D3/D700 (i.e. when compared to the original 5D).



Also removing the AA-filter (and when the lenses are not the limiting factor) will lead to funny demosaic'ing artifacts. This is not at all Foveon-like. It might fool the eye in to thinking that it's real detail, but it looks really ugly at 100%. Just look at a full size sharp Leica M9 image for example. With or without the AA-filter, a Bayer CFA still needs to combine roughly 3 adjacent photosite values in to 1 to produce 1 RGB pixel and this is the actual size of a Bayer "pixel" (i.e. 1/3 of the total photosite count). Foveon does this with 1. So Foveon can have a fewer larger number of pixels and get the same resolution.



Don't take my word for it... take a look here at the link below. This guy modified a 4.7MPixel Sigma SD14 to take EOS lenses and compared it against a 50D (15MPhotosites). The lens he used on both was the Canon 200 f/1.8L @ f/4 (i.e. very very sharp). The images are at their native resolutions, but if you upscale the SD14 image (e.g. bridge image) to match the dimensions of the corresponding 50D image, using a good upscaling algorithm, you'll see that it's difficult to tell them apart just by looking at the detail:



http://www.pbase.com/bigflat/sd14_50d



So that's the relationship between the Bayer CFA and Foveon designs... removing the AA filter doesn't equalise them.

[Guest]

[quote name='Brightcolours' timestamp='1285847839' post='3390']

Which brings us back to the reason Sigma images are "sharper"... due to the refusal to use AA-filters. If you remove the AA-filter from a Bayer CFA sensor, you will get the same kind of sharpness. Liked by some, disliked by those in the know (that is why most camera manufacturers put AA-filters in front).

[/quote]



I'm equally surprised by this claim - interpolated image always will be softer, AA filter or not. I guess the only situation where Bayer would be equally sharp is if someone created pure B/W sensor.

[Brightcolours]

[quote name='Lomskij' timestamp='1285921478' post='3418']

I'm equally surprised by this claim - interpolated image always will be softer, AA filter or not. I guess the only situation where Bayer would be equally sharp is if someone created pure B/W sensor.

[/quote]

It is not just a claim. Sharpness does not come from the colour information, but from luminance information. The luminance information is based on the information per pixel, mostly.



So, yes, a Bayer sensor without AA-filter gets about the same resolution as a foveon sensor without AA-filter.



An AA-filter is not something particular to a bayer CFA sensor. It is used to blur the image to such an extent that there are no details/edges that span less than 1 pixel, to avoid... aliasing. Aliasing happens just as much with a foveon sensor as with a Bayer CFA sensor. Aliasing is also known as "jaggies". Lines in images start to look like jagged lines, where you can see the individual square pixels, making false or wrong detail.

Aliasing can also create patterns, which are known as moire patterns. In the luminance area moire patterns show up equally with both bayer CFA and foveon sensors. The only thing that foveon sensors do not do is creating moire patterns in the croma space.



But AA-filters are not just there to avoid moire patterns with colours... yet that is the reason Sigma gives for not "needing" AA-filters. That is nonsense of course, foveon sensors without AA-filter have heavy aliasing (just not colour moire effects).



For those who like the aliased output, a the Sigma approach of course is fine. But it is incorrect to think AA-filters are only there to avoid colour moire effects.To me, aliasing in photos is just as unwanted as aliasing in computer graphics.



http://www.wfu.edu/~matthews/misc/DigPhotog/alias/

[Guest]

[quote name='Brightcolours' timestamp='1285930459' post='3420']

It is not just a claim. Sharpness does not come from the colour information, but from luminance information. The luminance information is based on the information per pixel, mostly.



So, yes, a Bayer sensor without AA-filter gets about the same resolution as a foveon sensor without AA-filter.

[/quote]



Hm. I was pretty sure that only half of the photo-sites in the Bayer sensor provide luminance information, and the remaining half (chroma sites) have that data interpolated from the neighbouring ones. While Foveon has 100% of photo-sites to provide the luminance data. So unless I'm totally wrong here, it's quite difficult to believe that, say, 10mpix interpolated from 5mpix would have the same sharpness as natural 10mpix image. With AA filter of without.

[Brightcolours]

[quote name='Lomskij' timestamp='1285932195' post='3422']

Hm. I was pretty sure that only half of the photo-sites in the Bayer sensor provide luminance information, and the remaining half (chroma sites) have that data interpolated from the neighbouring ones. While Foveon has 100% of photo-sites to provide the luminance data. So unless I'm totally wrong here, it's quite difficult to believe that, say, 10mpix interpolated from 5mpix would have the same sharpness as natural 10mpix image. With AA filter of without.

[/quote]

All "sites" deliver luminance information. Only interpolation of the data can give colour. It depends on the RAW converter just how much luminance information is being extracted, some are better at that than others. And of course, interpolation between the sensel values play part in it.



But it is wrong to think that because of interpolation luminance information (or data) is half of that of foveon sensors, that is simply untrue and just shows a lack of insight in the matter.



Which again still misses the major point: the sharpness of AA-filterless sensors is mostly FAKE detail. That you can measure fake detail as normal detail and think you get a lot higher resolution is of course true. Does not make the validity of the detail higher, though.

[boren]

Brightcolours, I'd be curious to hear your explanation for this:







(Source: dpreview.com)



The output from Sigma DP2 Foveon sensor shows no jaggies where in principle they should be (in a camera with no AA filter), while the output from the Pentax K10D Bayer filter does show them. What is going on?



I'm not a fan of Foveon sensors (I especially dislike the colors they produce), but I don't see any aliasing in the test samples. I may eventually find it if I look hard enough, but is it really such a big issue? At what print size and viewing distance do you expect to be able to see it? What percentage of viewers do you feel would notice it?

[Brightcolours]

[quote name='boren' timestamp='1285950051' post='3431']

Brightcolours, I'd be curious to hear your explanation for this:







(Source: dpreview.com)



The output from Sigma DP2 Foveon sensor shows no jaggies where in principle they should be (in a camera with no AA filter), while the output from the Pentax K10D Bayer filter does show them. What is going on?



I'm not a fan of Foveon sensors (I especially dislike the colors they produce), but I don't see any aliasing in the test samples. I may eventually find it if I look hard enough, but is it really such a big issue? At what print size and viewing distance do you expect to be able to see it? What percentage of viewers do you feel would notice it?

[/quote]

I can not tell what is what in those images, everything just will be guess work.



So, you see jaggies in the paperclips. Is each photo focussed the same, is each photo shot with the same sharpness of lens, same DOF and so on.



The only thing I am sure of is that those are in-camera JPEG images. We do not know the strength of the K10D AA-filter either (would need to look at that first).

If you look at the odd colours appearing in the small letters on the bottle, they could point to a very weak AA-filter for the K10D.



So we see sharpening artifacts, most probably. Not sure what you want to show with your sample, it is not exactly hard to find Sigma images with very clear aliasing.

[boren]

I'd be very interested to see real-life review that show that aliasing is indeed an issue with Foveon. I'm sure the effect can be demonstrated if one deliberately sets up the right conditions, subject, lighting and so on, but would it be visible in real life samples (as those in the end of the review at dpreview.com)?



Also, can you comment on the other points: "At what print size and viewing distance do you expect to be able to see it? What percentage of viewers do you feel would notice it?"