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Author Topic: SIGMA DP-1  (Read 32507 times)
61Dynamic
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« Reply #40 on: March 17, 2007, 01:14:11 PM »
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Oliver,

No one can view those images; they are set to Private. Besides it's irrelevant since those are just 2 images which is hardly enough to be telling of a cameras performance. And, not all images will display artifacts. The third issue is that in order to compare which two cameras can "capture color nuances better" you would have to capture the same scene in the same light with both cameras.
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:Ollivr
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« Reply #41 on: March 17, 2007, 03:04:18 PM »
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Oliver,

No one can view those images; they are set to Private.

OOps I am sorry. Wasnt aware that this affects direct linking as well. I changed it, again, here are the links.

http://www.flickr.com/photo_zoom.gne?id=423098427&size=o
http://www.flickr.com/photo_zoom.gne?id=423097304&size=o

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Besides it's irrelevant since those are just 2 images which is hardly enough to be telling of a cameras performance. And, not all images will display artifacts.

There are tons of more images on Pbase, FLickr and on Sigma's website everybody is free to look at. In this thread, an impression arose of Foveon images as full of artifacts and with less detail and worse color than a usual bayer image. I thought it might be interesting for some readers who have not looked at Sigma images so far to get an idea about how the Photos look straight out of the Raw converter without any processing. Maybe some will see certain aspects (capture of color nuances etc) they are missing in other cameras.

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The third issue is that in order to compare which two cameras can "capture color nuances better" you would have to capture the same scene in the same light with both cameras.
[{POST_SNAPBACK}][/a]
Even in such a "test" somebody would find a flaw..different sensor sizes..raw converters..lenses..etc. Therefore, to test anything wasnt exactly my intention but rather to provide an illustration after all this talk about nasty artifacts, lack of resolution and wrong colors. People can download these images, look at them, print them or whatever and draw their own conclusions. I see nothing wrong with that.

Sorry if it is of no interest to you. Maybe you will enjoy this here, though:

[a href=\"http://www.ddisoftware.com/sd14-5d/]http://www.ddisoftware.com/sd14-5d/[/url]

O.
« Last Edit: March 17, 2007, 03:27:43 PM by :Ollivr » Logged
Graeme Nattress
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« Reply #42 on: March 17, 2007, 03:12:50 PM »
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I definately see a fair bit of stair-stepping in the second of the two photos you link to.

Graeme
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KAP
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« Reply #43 on: March 19, 2007, 09:34:52 AM »
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I definately see a fair bit of stair-stepping in the second of the two photos you link to.

Graeme
[a href=\"index.php?act=findpost&pid=107202\"][{POST_SNAPBACK}][/a]

This camera has to be compared with the other point and shoots on the market, so colour this or that or artifact x or y needs to be seen in context with it's opposition, which is not DSLR's. I don't mean price competitors either, I mean a small camera that goes with you all the time. I don't think for one minute it will do everything or be perfect at what it does do. I can see it being better than the rest on offer though. i hope it works well and Sigma add to the range with other lens choices, I think this could out sell the the sd14 for Sigma. In fact I think when others see the demand for a quality P&S, Canon, Nikon etc will be rushing something to the market.

Kevin.
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BernardLanguillier
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« Reply #44 on: March 19, 2007, 07:05:27 PM »
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Indeed, think of a fixed 35 mm VR f2.8 lens, weather sealed compact body on top of a Nikon D80 or Canon 400D sensor... with RAW capture.

Sweet thought! I'd buy one instantly for 600 US$.

Cheers,
Bernard
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JLK
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« Reply #45 on: March 20, 2007, 08:29:24 AM »
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... i hope it works well and Sigma add to the range with other lens choices, I think this could out sell the the sd14 for Sigma...
Kevin.
[a href=\"index.php?act=findpost&pid=107470\"][{POST_SNAPBACK}][/a]

Indeed, I'm sure that is Sigma's expectations. And if it does well enough to bring additional SLR shooters into the SD14 (or next gen) dSLR fold, it will have an additional benefit.

My feeling is that this is Sigma's "budget" dSLR answer to the dRebel and D40.
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« Reply #46 on: March 20, 2007, 10:22:55 AM »
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Indeed, think of a fixed 35 mm VR f2.8 lens, weather sealed compact body on top of a Nikon D80 or Canon 400D sensor... with RAW capture.

Sweet thought! I'd buy one instantly for 600 US$.

Cheers,
Bernard
[a href=\"index.php?act=findpost&pid=107576\"][{POST_SNAPBACK}][/a]

Oh yes please, I can't see why they have not done this already. I wouldn't mind a wide camera, say Canon 16mp and a fixed super quality 20mm or wider with built in rise would be nice too. Hassel had the Super wide, others have made a quality wide so we know there's a market. I would pay lots more than $600.0, x by 10 and there would still be many buyers.
I hope this Sigma delivers.

Kevin.
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Petia
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« Reply #47 on: February 13, 2008, 03:36:27 AM »
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Or you could slip in a small sliver of glass, an anti-alias filter which really is an engineering necessity, take the resolution hit, but get smooth, continous images.

Graeme
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Well if you're willing to take the resolution hit of an AA filter, just use Gaussian blur in Photoshop. Spreading the photons or blurring the RGB levels are pretty equivalent with a Foveon sensor.
And leave the sharp, slightly aliased pictures to those who don't mind it. In practice as long as you don't have strong contrast, the aliasing seems not detectable.
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Petia
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« Reply #48 on: February 13, 2008, 04:04:41 AM »
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Softening jaggies after capture is not the same thing as never capturing them in the first place; same for any kind of aliasing. An AA filter (or a lens that effectivcely acts as one) filters away frequencies above the nyquist, so they are never captured. An unfiltered capture captures frequencies above the nyquist, and after capture, they are indistinguishable from other "mirror" frequencies below the nyquist. You have to filter away valid frequencies to remove the aliased ones.
You can find a sensor able to record frequency above the Nyquist frequency?? Maybe you should reread your Signal Processing textbook, no? What happens is that the Foveon is able to record signal at Nyquist frequency whereas a standard Bayer cannot, due to the low-pass AA filter in front of the sensor. Whether it is desirable or not to resolve Nyquist frequencies is another question. The jaggies would probably not annoy you if the pixel resolution was 3x higher as in a classic Bayer. After all, the only thing that counts is whether you can see them in print or at usual display magnification.

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There is a strange idea going around that a digital camera should be able to record a black pixel next to a white one. It is impossible to do so, and have an accurate recording.
I'm curious to know why...

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What all cameras need for better *real* subject sharpness is more pixels; technology and storage issues are holding that back. With enough pixels, color resolution is no longer an issue with Bayer arrays, and aliasing is no longer an issue (no AA filter needed). Bayer is currently ahead in the miniaturization race.
With a Bayer array, AA filtering is always necessary to distribute light over neighboring photosites, otherwise you're not able to differentiate color close to Nyquist frequency. In other words, you are not able to tell the difference between a tiny white reflection and a colored one. No AA filter = color artifacts.
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Graeme Nattress
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« Reply #49 on: February 13, 2008, 07:21:15 AM »
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A post blur of a sampled image is NOT the same as a pre-blur before sampling. That's he problem with aliases - once they get into the system they cannot be got out easily. If they could be removed by a small gaussian blur, we'd all not be bothered by aliases, and we'd just post-blur when necessary. But it doesn't work like that. I'd remember that Foveon themselves say that their sensor still needs an OLPF but Sigma ignore this.

Graeme

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Well if you're willing to take the resolution hit of an AA filter, just use Gaussian blur in Photoshop. Spreading the photons or blurring the RGB levels are pretty equivalent with a Foveon sensor.
And leave the sharp, slightly aliased pictures to those who don't mind it. In practice as long as you don't have strong contrast, the aliasing seems not detectable.
[a href=\"index.php?act=findpost&pid=174490\"][{POST_SNAPBACK}][/a]
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Ray
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« Reply #50 on: February 13, 2008, 09:08:47 AM »
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Again, since nobody seemed to have noticed.
Can somebody show me the artifacts in those two images made with the older SD10? I am having a hard time here finding some. And I would be interested in an assessment about in which regard a bayer camera would capture color nuances better.
On a side note, I severely struggle to find the chroma noise in the shadows as well. Must be my monitor. Note this is unphotoshopped unsharpened raw converter output of an old Sigma DSLR.
[a href=\"index.php?act=findpost&pid=107134\"][{POST_SNAPBACK}][/a]

You've used a very strong 'effective' AA filter in these shots; out-of-focusness. Many of the shadows are OoF and there are only small areas in each shot that are in focus.

Nevertheless, I don't see any major problem with artifacts in any of the Foveon images that I've viewed on my monitor, and as we all know, users of MFDBs seem to be very pleased with the superior results they get, claiming that a 20mp DB without AA filter produces noticeably superior results to a 21mp 35mm dslr.
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Petia
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« Reply #51 on: February 13, 2008, 10:09:37 AM »
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A post blur of a sampled image is NOT the same as a pre-blur before sampling.
Graeme
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Sorry Grame I don't see your point. Imagine photons falling into bins. You can distribute them with a physical filter over a larger area. Then your photon counts will be exactly those you'd have without filter, convoluted by the mathematical filter (kernel) that matches your physical LPF (it may not be exactly Gaussian of course). If your physical LPF is not dispersive (which is to be hoped for) then it's the same filter for all RGB levels.
I don't see how applying a convolution on RAW data can be any different from having a physical LPF, (if we neglect the slight difference due to photons falling on photosite borders, of course).
I bet the differences you are reporting are due to blurring PROCESSED, sharpened images.
Yes there is natively a small artificial contrast induced by photosite borders, but if your raw converter allows applying a slight preblur before any other treatment, then you shouldn't see any aliasing at all. That's something fairly easy to implement in a raw converter, especially if users ask for it. So I don't see why having no physical LPF is a design flaw.
If you can show me evidence of the contrary, I'm ready to change my mind. :-)
Anyway applying low sharpening for Foveon images should solve your problem in practice. The only reason Sigma oversharpen them is to visually match 12 MP images. I don't mind slighty lower subjective resolution, especially for a compact camera. And the lower pixel count means I can put twice as many images on a memory card!
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Graeme Nattress
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« Reply #52 on: February 13, 2008, 10:17:11 AM »
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It's very , very different. Blur then sample is very different to sample then blur! That's because aliasing happens at the point of sampling when too high frequencies enter the system. If you stop them arriving at the sampling, aliasing and moire never occur. If you let them through sampling, they fold back into the image an appear at lower frequencies (hence the name alias) so that the amount of blur needed to remove them, especially in the case of moire, will remove all detail from  the image. I'd read through Alan's post here: http://forums.dvdoctor.net/showthread.php?...hlight=aliasing about aliasing as that will explain the situation much better than I can.

But put it this way - an OLPF is expensive, and software is  cheap. If you  thought that software blurring could do the same as a physical OLPF, don't you think camera manufacturers would do  so? It would be much cheaper, and totally user configurable from full through none, and would  make everyone really happy! But, you see, it doesn't work that way, so we have to do it properly and expensively with a real physical before the sensor filter.

Graeme
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EricV
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« Reply #53 on: February 13, 2008, 01:19:20 PM »
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Here is a simple example of the difference between "blur then sample" and "sample then blur".  Imagine a thin line of illumination running diagonally across a sensor.  To be definite, lets say the line starts at the corner of a pixel and traverses two pixels horizontally for one pixel vertically.  An optical system with no blur will produce an image with a "staircase" pattern.  Now blur the line by a fraction of a pixel.  This will spread some light into pixels barely touching the original line, partially filling in the corners of the staircase pattern.  But note that there will be no light added to pixels which do not contain the blurred line.  Contrast this to the case where the image is blurred after sampling.  The corners of the staircase pattern will again be filled in, but light will also be added to more distant pixels which do not contain the blurred line.
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EricV
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« Reply #54 on: February 13, 2008, 01:23:30 PM »
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Here is a simple example of the difference between "blur then sample" and "sample then blur".  Imagine a thin line of illumination running diagonally across a sensor.  To be definite, lets say the line starts at the corner of a pixel and traverses two pixels horizontally for one pixel vertically.  An optical system with no blur will produce an image with a "staircase" pattern.  Now blur the line by a fraction of a pixel.  This will spread some light into pixels barely touching the original line, partially filling in the corners of the staircase pattern.  But note that there will be no light added to pixels which do not contain the blurred line.  Contrast this to the case where the image is blurred after sampling.  The corners of the staircase pattern will again be filled in, but light will also be added to more distant pixels which do not contain the blurred line.   (I tried to attach images illustrating this, not sure if they will make it.)
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John Sheehy
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« Reply #55 on: February 13, 2008, 05:09:01 PM »
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(I tried to attach images illustrating this, not sure if they will make it.)
[a href=\"index.php?act=findpost&pid=174620\"][{POST_SNAPBACK}][/a]

I saw the attachment earlier today, but it is gone now.
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Petia
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« Reply #56 on: February 17, 2008, 02:17:26 PM »
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You have a point, but a weak one. You're telling me that frequencies *above* Nyquist frequency will translate to artifacts (folding back to lower freqs) if you haven't filtered them out. That's true. These artifacts will be luminance artifacts (and not moire, since the Foveon will never give you color artifacts). Your example with the fine line is exactly similar, you're speaking frequencies above Nyquist. But you should think about the size of your 'fine line'.
A Foveon sensor has photosites < 8 micrometers wide, which on a 20.3 x 13.7 mm sensor translates into a Nyquist freq of 64 lp/mm. Now if you're shooting with super-heavy tripod and leica glass, you may encounter this limit. Normal people, hand-held camera, sigma lens... it'll be far enough low-pass filtering, you'll never reach strong signal at 40 lp/mm. So you may think it's stupid not to put a OLPF in a DP1, but for me it's just common sense.
The only real problem with the DP1 how they'll handle the color noise. The rest is phantasm.
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John Sheehy
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« Reply #57 on: February 17, 2008, 05:09:15 PM »
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The only real problem with the DP1 how they'll handle the color noise. The rest is phantasm.
[a href=\"index.php?act=findpost&pid=175500\"][{POST_SNAPBACK}][/a]

The images *ARE* aliased, despite all of your theorizing to the contrary.  How can you miss it?  Facial hair stubble that appears in some cases as a slight darkening of two lines of pixels, and in other cases, solid pixels of hair, exactly one pixel wide, and exactly two pixels long, and in the presence of other such stubble, in an obvious grid with no sub-pixel precision.  Happens quite frequently.  Aliasing is rampant in Sigma images.
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Petia
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« Reply #58 on: February 17, 2008, 06:35:40 PM »
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The images *ARE* aliased, despite all of your theorizing to the contrary.  How can you miss it?  Facial hair stubble that appears in some cases as a slight darkening of two lines of pixels, and in other cases, solid pixels of hair, exactly one pixel wide, and exactly two pixels long, and in the presence of other such stubble, in an obvious grid with no sub-pixel precision.  Happens quite frequently.  Aliasing is rampant in Sigma images.
[a href=\"index.php?act=findpost&pid=175535\"][{POST_SNAPBACK}][/a]


I'm simply saying:
1. The absence of anti-alisaing filter will never be a problem for the DP1
2. The aliasing you complain of is mainly due to *oversharpening* images in order to make them appear as sharp as 12 MP images.

As I suppose you routinely print 20 x 13.3" prints that you look at 10 inches, you're certainly very worried about this. I am not, and I reckon many people here aren't either.

But before I can take your comments seriously, you'll have to shoot with the SD14 (or DP1, if ever it comes), set the image processing parameters to what suits you the most, and be still dissatisfied with the results.
I suspect you have never hold an SD14 in your hands, never tried to, and never printed a Sigma image to any size. Am I wrong?
« Last Edit: February 17, 2008, 06:37:08 PM by Petia » Logged
John Sheehy
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« Reply #59 on: February 17, 2008, 08:17:07 PM »
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I'm simply saying:
1. The absence of anti-alisaing filter will never be a problem for the DP1

It already is for the SD14, and the DP1.  They have too few pixels to have aliased pixels.

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2. The aliasing you complain of is mainly due to *oversharpening* images in order to make them appear as sharp as 12 MP images.


No.  Aliasing due to over-sharpening is different from aliasing due to aliased capture.

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As I suppose you routinely print 20 x 13.3" prints that you look at 10 inches, you're certainly very worried about this. I am not, and I reckon many people here aren't either.

I can see the aliasing with the images downsampled to fill my monitor.  That's all I need to have a problem.

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But before I can take your comments seriously, you'll have to shoot with the SD14 (or DP1, if ever it comes), set the image processing parameters to what suits you the most, and be still dissatisfied with the results.

You don't seriously think the JPEG settings are going to affect the aliasing of the capture, do you?

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I suspect you have never hold an SD14 in your hands, never tried to, and never printed a Sigma image to any size. Am I wrong?
[a href=\"index.php?act=findpost&pid=175545\"][{POST_SNAPBACK}][/a]

You don't have to handle a camera to tell things about its IQ.  Are you serious?  You're clutching at straws.

I'd be very embarrassed if that was what I had to resort to in order to defend my position.

But I have printed Sigma samples, and I can see the aliasing in them.

It seems that most people are blind to aliasing.  It's not just Jaggies - that's just one artifact of aliasing.  There is a very general, and obvious (to me) redistribution of the analog image in a snap-to-grid effect that makes aliased captures look unnatural, and incompletely sampled.
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