M8 at f8 on a California Freeway and Moire at 60mph! [Archive]

Ray West

December 12th, 2006, 02:12 AM

Hi Asher,

As you know, Moire is the result of similar regular patterns being superimposed, Wikipedia has some info (and calculations) but plenty more out there. It is a compromise, if you make digital cameras, which have a regular sensor pattern, as to how you blur the image, before it hits the sensor. It will happen, sooner or later with all sharp digital camera systems. If it seems that the weaker filtering on the M8 allows moire to occur more frequently, and if Leica do something about it, then the image is likely to suffer in some other way. If you downsample, or upsample the image, choose a different print resolution, I think you can diminish the printed effect, in a similar way as zooming on the screen alters it. Anyway, I suspect selective treatment in pp will cure it.

At the moment, it looks as if the M8 is only reliably useful for natural landscapes. I would be interested to see a shot with the M8 showing moire, compared with the same shot from a 'lesser' camera.

Best wishes,

Ray

Ray West

December 12th, 2006, 02:37 AM

Hi Asher,

If I zoom out on your image, then I get the moire as a result of the 'road lines' interfering with the vdu screen dot pattern. This pattern moves, depending on the image size. If I zoom out, I get the moire pattern within the image itself. I do not know if jpeg adds to this, but at high magnification, I can see that the fringe pattern is blurred, whereas the normal pattern is pixelated. At the normal size, the pattern is not that noticeable on my screen.

This puts another factor into the equation, the image conversion method. (I know your original would be raw, but even that is 'converted' to some extent.)

Best wishes,

Ray

Asher Kelman

December 12th, 2006, 02:52 AM

Hi Ray,

All one is doing when you change magnification is altering the coincidence of cycles. Moire will peak, then gradually go down then peak again in cycles as you increase or decrease the magnification. One can shift the moire up and down the patterning of the actual image.

However, it is always there.

No need to obsess just print the file.

I even printed directly from the PSD file at 360 dpi without any manipulation and we get the same moire in the 8x10 print!

Try it for your self! It's the M8 file!

Asher

StuartRae

December 12th, 2006, 03:24 AM

This puts another factor into the equation, the image conversion method.

Asher,

Assuming you did save the image in RAW format, have you tried different converters?

I know that RSP was often guilty of colour artifacts, but this could be cured to some extent by decreasing detail extraction. Alas RSP is no more and so doesn't support the M8.

Regards,

Stuart

Ray West

December 12th, 2006, 04:35 AM

Hi Asher,

Maybe I wasn't clear in my last post. I am saying that my initial response, re the zoom etc. is connected with the screen resolution and the near parallel lines in the road surface. That sort of interference can usually be removed by printing, or viewing, at different resolutions. This gives the moving patterns, it is not related to the camera sensor (although if the sensor did not resolve the lines in the first place.... ). However, if you zoom in on your image, beyond the pixel level, you can see the moire due to either the camera sensor itself, or the jpeg conversion or even the raw conversion process. the 'rings' are clearly blurred (oxymoron ;-) .

I have an image here, http://www.openphotographyforums.com/forums/showthread.php?t=1251which has similar artifacts (penultimate posting). If my original is in raw, I will see if different convertors change it, as Stuart indicates.

Best wishes,

Ray

StuartRae

December 12th, 2006, 06:14 AM

In his article (http://www.normankoren.com/Tutorials/MTF2.html#Nyquist) about the Nyquist frequency and aliasing, Norman Koren suggests that aliasing can be reduced by stopping down to about f/16, at which point diffraction acts as an AA filter.

Regards,

Stuart

Nathaniel Alpert

December 12th, 2006, 07:02 AM

There seems to be tremendous confusion among photographers about antialiasing filters and digital imaging. On the other hand, this phenomena is well understood in digital signal processing; all of our digital toys are desigend according to the Shannon sampling theorem. One way to think about this issue is to imagine that a "virtual image" is projected onto a plane at the level of the sensor. This image is "sampled" by the sensor at a finite number of locations. If the virtual image has no information above the Nyquist frequency of the sensor, one can "reconstruct" the virtual image exactly, assuming the image is noiseless. If the virtual image contains significant information in the frequencies above the Nyquist frequewncy of the detector, there will be alaising (Moire). It will be more or less objectionable, depending on the scene (e.g. fabrics) and the quality of the lens. The engineering solution is to interpose a filter that will cut off all information above the Nyquist frequency of the sensor, on the grounds that there is no free lunch. This works, but the filters are not perfect; they cannot cut everything off without some blurring below Nyquist. Without a proper antialiasing filter, the M8 will exhibit alaising. It is there all the time, not just when you image a fabric or hairs. Aliasing is a distortion that places high frequency information in the wrong place in the image. One can argue that this will not be objectionable in a landscape because it is spread throughout the image, but I think that a properly designed camera with a well-designed AA filter and a good lens should outperform the camera with an equally good lens and no AA filter. The problem in evaluating this assertion is that in the real world, it is difficult to remove the lens from the evaluation. Measuring the same camera and lens with and without AA filters would be the best experiment.

' Hope this helps.

James Roberts

December 12th, 2006, 07:11 AM

{snipped} The problem in evaluating this assertion is that in the real world, it is difficult to remove the lens from the evaluation. Measuring the same camera and lens with and without AA filters would be the best experiment.
Hope this helps.

Nathaniel--it's probably an experiment that Leica did already, don't you think? Or--purely conjecture here--could there have been some other optical reason for the very weak AA filtering (I'm not entirely sure about "lack") in the DMR and M8?

All I know is practically with the DMR I don't run into artifacts that mar prints any more than I would with my 1ds2 (yes, in C1 from time to time I'd see moire there too--especially in fabrics).

Asher--I haven't had time to print your shot; I think the suggestion for different converter is a good one, though.

Ray West

December 12th, 2006, 07:21 AM

Hi Asher & Stuart,

fwiw, my original image was a crw file, my version of canon dpp does not work with it. However, in Silkypix, Light zone, cr2, & even Irfan view, all set to 300% magnification, there is only a slight amount of moire visible - there are worse things going on. However, it is clearly seen that it is about the mid image area, where the sensor gives up resolving the ridges in the walkway. This is exactly as I would expect it to be, being so wise after the event. There are differences in the colours/noise that each raw viewer shows, but in this particular moire test, they all show more or less the same artifacts.

Now, my jpeg version, 'freezes' the image at whatever resolution is chosen, and picks up the moire pattern, in a similar way it would be shown on screen at that resolution. If you zoom in, you see that the pattern stabalises, showing that captured moire, which is far more moire than in the raw image, what you see in the jpeg as moire has little connection with the sensor. If you zoom out, you see the moire effect, as the thin straight lines interact with the fixed pixels of your monitor. I think the same may apply to Asher's image too, maybe we could have a peek at the raw image.

Best wishes,

Ray

Nathaniel Alpert

December 12th, 2006, 08:10 AM

Issues about aliasing are covered in digital imaging 101. It is hard to believe that Leica did not know exactly what they were doing. I don't think it is useful to speculate on their rationale.
On the other hand, I have read that the physical space between lens and sensor in the M8 makes it difficult to include an AA filter (and IR as well) but I don't know that for a fact. Life is full of compromises.

Asher Kelman

December 12th, 2006, 09:13 AM

I am a great advocate of the M8. I can use it where the 5D with lenses is more noticable. The bag with lenses weighs nothing and the files are wonderfully robust and the pictures great!

BTW, it prints with moire at 300 dpi from a PSD file with no uprezzing of the file size!

I'll send anyone the file for processing or curing to the extent possiblle!

Cheers!

Asher

Don Lashier

December 12th, 2006, 10:27 AM

Asher, have you tried C1's moire filter? It usually does a pretty good job.

- DL

Asher Kelman

December 12th, 2006, 03:39 PM

Ray West

December 12th, 2006, 06:53 PM

Hi Asher,

The only Moire I see, is in your lane, just behind the vehicle in front of yours, at the edges, where the grooves in the road surface become blurred. It seems to be red and green fringing. I have only loaded the file into Lightzone. I have had a play, but not good enough to give a definitive answer, since I am not an expert at the capabilities of lightzone. I think the easy solution, would be to select the region, being generous, and using a broad feather, and then blur it. The road beyond is blurred, i.e. the camera sensor can not resolve the grooves, you're simply bringing that area forward a few yards. I guess other solutions would be to clone the smooth road forward, but I couldn't get LZ to clone sensibly. It may be, that some of the chromatic aberation fliters in more advanced editting software could do it. As it is, it is not noticeable at 'actual pixel size' on the screen. It is exactly tthe same characteristics as in my image, mentioned previously, in that it is not the same in raw as in the jpeg, and the same sort of area gives the fringing.

I think, compared to the other qualities in the images that the M8 seems to produce, I'd prefer to keep the colour range and detail, rather than sacrifice it for reducing the odd bit of moire fringing. There is a fair amount of detail in there.

Best wishes,

Ray

Nathaniel Alpert

December 13th, 2006, 05:59 AM

Remember, this is an excercise and I do not see it as a criticism of the camera, since I have not as yet found that it hurt anything I seriously wanted to do. Yet I'd like to know about it so I can work around these phenomena.

Here's the file for download! (http://download.yousendit.com/BC6CF35D1697AAC1)

Please pm me that you have downloaded it OK.

Thanks so much for having a go!

Asher

The fact that the M8 does not have an effective (any?) AA filter means that it will always exhibit aliasing. Aliasing (Moire) cannot be removed by any filter without additional information about the scene. What this means is that although the images from the M8 may be better in some way than those from other cameras, because of aliasing they are not as good as they could be. Ordinary photgraphers cannot evaluate the sensor without also considering the lens as part of the system. Lieca lenses are legendary, they may be contributing much of what people like about the M8 pictures, due to their perfromance below the Nyquist frequency of the sensor. On the other hand, very sharp lenses pass more high frequency information to the sensor and thus there may be more trouble with aliasing. It is important to understand that there will always be aliasing in every image, the only question is whether its presence will outweigh the other virtues of the M8.

James Roberts

December 13th, 2006, 08:56 AM

I have seen no trouble to date with aliasing and the M8. Quite the opposite; so far, it's doing as well as the 1ds2 and perhaps even better with detail.

Asher Kelman

December 13th, 2006, 02:59 PM

Jamie,

Have you looked at this DNG file? Here's the file for download! (http://download.yousendit.com/BC6CF35D1697AAC1) It would be interesting to see whether or not you see the moire as a file issue or an interaction with the screen or printer to get the moire.

It certainly is visible and always prints out from a PSD file.

Asher

Will_Perlis

December 13th, 2006, 03:36 PM

Ray West

December 13th, 2006, 04:08 PM

Hi Asher,

The areas where you have fringing due to the camera sensor and the road surface are within patches which I've shaded green, below. Check it on your raw convertor, see if its the same as what I see. Keep zooming in, until the pattern stabalises. (probably red and green swirls, roughly within the area shown)

http://www.yertiz.com/images/L1030676M8%20MOIRE-1.jpg

All other artifacts, outside of those patches, when printing or viewing on screen are due to interference patterns between the image and your print/view device. Unless you zoom in on the image, as I keep mentioning, you could be talking about moire patterns other than those caused by the actual object and camera sensor. I do not think it is a significant problem, unless you are upsizing the image, since it can be cloned out. I do think you may have a problem in finding a suitable print resolution to overcome the natural interferance between the lines in the road, and your print head. I wonder if a dye sublimation print would be different.

Best wishes,

Ray

James Roberts

December 13th, 2006, 07:33 PM

Asher--I've looked at the file enough to develop it out of C1 and print a quick test (ImagePrint, 4000, 8 x 12 @ 300ppi).

I'm not seeing a "moire" pattern on the prints so far.

I also don't see moire, I don't think, on my monitor (1280 * 1024 EIZO) looking at the developed TIFF @ 100% in PS CS2.

I see the moire effect of the screen and road at almost any other magnification. But PS does funny stuff at more or less than 100% magnification.

What I *do* see on the monitor at 100% is some very subtle grey-green-ish artifacts right at "focus extinction" (where those parallel lines stop becoming lines). This could be some kind of aliasing, but it's very subtle. This is probably what Ray is talking about...

And I'm not sure I would have noticed it at all if I hadn't been looking for it--the artifacts are not printing exactly the same way they're displaying.

Of course, I'm also not sure there isn't some weird visible artifact in the shot actually there on the road--that diagonal white line "scratch" on the concrete is actually pretty astounding detail. I guess it could be something on the windsheild, too... you did shoot this through a windsheild, right Asher? ;)

I tried the C1 moire plug-in and the on-screen effect actually got worse after the plugin completed, which is also strange.

Asher Kelman

December 13th, 2006, 10:28 PM

What I *do* see on the monitor at 100% is some very subtle grey-green-ish artifacts right at "focus extinction" (where those parallel lines stop becoming lines). This could be some kind of aliasing, but it's very subtle. This is probably what Ray is talking about...

Of course, I'm also not sure there isn't some weird visible artifact in the shot actually there on the road--that diagonal white line "scratch" on the concrete is actually pretty astounding detail. I guess it could be something on the windsheild, too... you did shoot this through a windsheild, right Asher? ;)

No I shot out of the right passenger window! Outside, totally outside!

I tried the C1 moire plug-in and the on-screen effect actually got worse after the plugin completed, which is also strange.
James, this, I believe is real.

BTW, Will Perlis first used the camera in Samy's Camera in Los Angleles. He immediately had severe moire in the first pictures. I have had a different experience until now.

All my pictures are beautiful. The artifact is real but it doesn't take away my admiration for the M8. Just look at the New York Central Park pictures of Steve Teitelbaum.

I'll do some more work on this.

The moire prints out easily from CS2. Try it at 300 dpi. File prepared in Adobe RAW.

Still puzzled but a fan!

Asher

Bart_van_der_Wolf

December 14th, 2006, 05:00 AM

Have you looked at this DNG file? Here's the file for download! (http://download.yousendit.com/BC6CF35D1697AAC1) It would be interesting to see whether or not you see the moire as a file issue or an interaction with the screen or printer to get the moire.

Asher, it is camera induced moire, no doubt whatsoever.

Since the red and blue filtered sensels sample the image projected on it more sparsely than green-filtered ones, there will always be a difference (whether AA-filtered or not) in the onset of moire visibility as one approaches the so-called Nyquist frequency. This will result in false color artifacts, the amplitude of which also depends on the Raw converter used.

An AA-filtered sensor, probably impossible to implement with such close proximity between lens exit pupil and sensor as in the M8, will only reduce the aberrations. Total eliminaton would result in significant loss of resolution, a trade-off not chosen by manufacturers of traditional Bayer CFA designs. A more gentle roll-off is common, although there are differences between designs.

The lack of an AA-filter will always result in more Aliasing artifacts, but they may not always be disturbingly visible. An AA-filter will always reduce the amplitude of Aliasing artifacts, but also reduce the MTF of the system's limiting resolution (although some of that reduction can be restored in Postprocessing).

Bart

Bart_van_der_Wolf

December 14th, 2006, 05:27 AM

There's some component that's related to the screen and magnification. Here, in PS with a 1280x1024 LCD at 33% it's very apparent, at 50% it almost vanishes and it comes back strongly at 66%. I'll be curious to see what happens on the 1600x1200 LCD.

The effect you see is caused by (quick but inaccurate) down-sampling without proper anti-aliasing precautions. That 'zoom-effect' is most visible at reduction factors other than 1/2 x

Bart

Ray West

December 14th, 2006, 05:45 AM

StuartRae

December 14th, 2006, 09:26 AM

I don't know if anyone's looked at the embedded JPEG (320x240) from the DNG file, but having just had a look at Bart's very interesting article about down-sampling algorithms it does seem to confirm his theory.

It also reinforces my initial unease about the purple sky.

Here it is at 200% for better visibility.

http://web.ukonline.co.uk/sw.rae/examples/embedded-jpg.jpg

Regards,

Stuart

Asher Kelman

December 14th, 2006, 09:33 AM

Stuart,

This shows it is not just the distant lines that cause problems.

Also no machine makes marks like this by cutting straight lines into concrete! Not even in California with a tankful of speed!

So beware of sending your great fashion/newstory pictures as jpgs to any magazine editor!

What are the mathematical rules for minimizing this? Who has gotten rid of them with any method?

Asher

ian sanderson

December 14th, 2006, 09:56 AM

Asher,

Just to let you know I downloaded the file. The moiré is quite evident and is cause for concern from my point of view as I am/was close to buying the M8. I wonder if the ISO 640 has got anything to do with it as noise mixed with the lines in the concrete might not help. I also noticed a lot of dust on the sensor, not wanting to change the subject but is the M8 easy to clean?

Kind regards

Ian

StuartRae

December 14th, 2006, 12:10 PM

I downloaded the file and converted it with the only option available to me, ACR 3.6.

Interestingly there were no artifacts in the parallel lines ahead of the car at 100%. (not to say there weren't some elsewhere)

Then I down-sampled to 800px width using different algorithms. This clearly demonstrated that down-sampling does produce artifacts, and that their severity depends on the method used.

100% Crop

http://web.ukonline.co.uk/sw.rae/examples/Original.jpg

Comparison of down-sampling methods

http://web.ukonline.co.uk/sw.rae/examples/Resampling.jpg

Regards,

Stuart

StuartRae

December 14th, 2006, 12:51 PM

James Roberts

December 14th, 2006, 01:30 PM

Hi James,

Thanks for confirming what I see on the original image. The rest of what is talked about here, is nothing to do with how the camera handles the real world, but how us folk handle the resulting digital image. Its very similar as with video/tv, avoid striped shirts! Possibly, printing at some odd resolution may reduce the visibilty of the artifacts, say at 313 dots per inch may alter things slightly, possibly 433dpi may alter it more.

Since the individual sensor sites are arranged on a regular pattern, green probably being different to the others, then I could expect the colours to be seperated, as we saw.

Best wishes,

Ray

Ray, you're absolutely right. The RIP I use to print is also not using PS output, so that may have something to do with me not seeing the patterns (except of course when zooming the screen).

As I said Asher, I believe what you're seeing is real--the fringing--but the interference patterns are definitely the RAW converter.

I don't believe ACR is ready for the M8 yet, actually. I know it's official with ACR 3.6, but the quality out of C1 is much better IMO.

At 100%--the only magnification at which to judge at all in PS--I just don't see typical moire patterns. Fringes, yeah--which is odd enough--but not moire patterns.

So there's something odd going on here--probably some slight aliasing. Hard to tell for sure though, because it's that slight in prints.

Ray West

December 14th, 2006, 05:08 PM

Hi James, et al,

There is nothing odd going on here at all. It is what is expected if you have lines or patterns that do not quite line up with other lines or patterns. Just spend a few minutes with google search on 'moire', etc. Plenty of examples, some of which will 'hurt your eyes'.

Take a picture, with any camera, film if you wish, of similar converging patterns, or just get a cad program or even photoshop, and draw something similar. Then adjust it, so that it 'crosses the pitch' of the display device, either vdu or printer. you will get exactly the same sort of effects as Stuart has shown. As I keep saying, it is not camera related, other than its a sharp image. There are lines in the road, which may or may not be enhanced by the image processing, but they are there, else Asher has a very, very, peculiar camera.

I fail to see what the problem is with the camera - there is no moire, other than the slight effects in the regions I highlighted, as far as I can see. What is being discussed now is a different problem - one of 'how to print a digital image on a digital printer.'

wrt downsampling, if you do it to a slightly different scale, you will see the pattern move, as the pixels hit/miss the region under consideration. Qimage gives a good selection of algorythms, some will be better than others, but all, since they use a regular pattern, will have some sort of fringing occurring. Until software is designed with some sort of AI, you have to correct for it manually. It is a benefit of digital ;-)

Best wishes,

Ray

Bart_van_der_Wolf

December 14th, 2006, 05:47 PM

wrt downsampling, if you do it to a slightly different scale, you will see the pattern move, as the pixels hit/miss the region under consideration. Qimage gives a good selection of algorythms, some will be better than others, but all, since they use a regular pattern, will have some sort of fringing occurring. Until software is designed with some sort of AI, you have to correct for it manually. It is a benefit of digital ;-)

In fact, by my request, Mike Chaney did include a type of AA-filtering for down-sampled images in Qimage. The user has a selection of several levels of filtering, but IMHO the default strikes the best balance between aliasing artifacts and blurring (although, again IMHO, not optimal but better than most).

On up-sampled images this will not have any effect. In general, magnification of an image will also magnify (aliasing) artifacts. The aliasing, if visibly disturbing, should be prevented before capture. Otherwise there is little else (other than local color channel editing/blurring) left to mitigate the issue. Prevention is still better than cure ...

Bart

Bart_van_der_Wolf

December 14th, 2006, 06:07 PM

I don't know if anyone's looked at the embedded JPEG (320x240) from the DNG file, but having just had a look at Bart's very interesting article about down-sampling algorithms it does seem to confirm his theory.

Just in case one wonders, Stuart is (probably) referring to my theoretical (http://www.xs4all.nl/~bvdwolf/main/foto/down_sample/down_sample.htm) and practical (http://www.xs4all.nl/~bvdwolf/main/foto/down_sample/example1.htm) down-sampling example pages. As sensor sizes increase, the chance of having to down-sample increases (e.g. for web publishing of samples), so I created those pages in an attempt to avoid having to repeat myself ... http://www.openphotographyforums.com/forums/images/smilies/redface.gif

Those pages demonstrate artifacts due to down-sampling, making it 100% certain that detail will hit the capability limits of faithful reproduction in a regularly sampled discrete image, although similar effects can be expected from under-sampled sensor images, like the one discussed in this thread.

Bart

Ray West

December 14th, 2006, 06:23 PM

Hi Bart,

Whatever you do before the light hits the sensor, will be a trade off, as you mentioned earlier. I believe that all you do is shift the problem further away, without solving it. I think, since it is digital artifacts, that a digital solution, i.e. software, will provide the answer. It's just, at the moment, nobody, afaik is really looking at getting a solution. I'm thinking it would need some in built intelligence, to detect the interference patterns, and blur them out, or whatever, in that area only. A sort of auto morphing tool, to give a gentle change between the blurred distance, and the sharper mid ground, in this instance. If this particular image was worth the effort, maybe an hour with a brush tool, or five minutes if I was sixteen years old ;-)

When you think about it, adobe and the like are so primitive, its quite unbelievable, a bit like trying to travel to the moon by horse and cart....

Best wishes,

Ray
.

Bart_van_der_Wolf

December 15th, 2006, 04:01 AM

Hi Bart,

Whatever you do before the light hits the sensor, will be a trade off, as you mentioned earlier. I believe that all you do is shift the problem further away, without solving it.

Hi Ray,

I agree that AA-filtering is not a solution, but it is an attempt to prevent it from happening. Mathematically aliasing is an easy problem to prevent, just remove the highest spatial frequencies in the projected image before it hits the regularly spaced sensels. The catch is that it will reduce the resulting resolution by a factor of 2-3. Given that aliasing artifacts are not always as obvious as in the example shown in this thread, or they can sometimes be remedied rather easily after the fact, most of us are unwilling to pay the price of lost resolution just to be on the safe side.

The most elegant prevention is the use of an AA-filter, since it strikes a balance between reducing the chance of producing artifacts with only a limited impact on resolution. Because it is not optimal (or probably even possible in the M8), there will still be a need for some postprocessing. However, if we start without any prevention the task will be much harder.

I think, since it is digital artifacts, that a digital solution, i.e. software, will provide the answer. It's just, at the moment, nobody, afaik is really looking at getting a solution. I'm thinking it would need some in built intelligence, to detect the interference patterns, and blur them out, or whatever, in that area only.

The real problem here is that the larger sized aliases of impossible to reliably image small features (smaller than 2 samples, or 4 pixels in a Bayer CFA) are intermixed with real detail, and it has become impossible to remove one without damaging the other. That's why it should be prevented before it happens.
I agree that since human vision is good at spotting unexpected patterns, there may be some room for AI solutions in the future, but again it can't be perfect.

A sort of auto morphing tool, to give a gentle change between the blurred distance, and the sharper mid ground, in this instance. If this particular image was worth the effort, maybe an hour with a brush tool, or five minutes if I was sixteen years old ;-)

When you think about it, adobe and the like are so primitive, its quite unbelievable, a bit like trying to travel to the moon by horse and cart....

Yes, there is still a long way to go, but the laws of physics will pose a solid restriction on what can ultimately be done. I remain a strong advocate for 'prevention is better than cure', because GIGO (garbage-in garbage-out) still rules, even if we get better tools to cover things up a bit.

Sofar, as a postprocessing kludge, I occasionally use a severely (color)noise reduced layer or even blurred layer with mask to locally reduce the visibility of the most glaring artifacts. Local desaturation may also help somewhat in the case of false color artifacts.

Bart

Ray West

December 15th, 2006, 06:23 AM

Hi Bart,

Thanks for your considered reply. I agree with what you say, but I personally think, whatever that may be worth, that the balance leica have is not too bad - just avoid tapered stripes... In more 'natural' scenes, its not a visible problem, afaik, but to be honest I've not checked in any detail. For example, I do not think there have been any complaints here, http://www.openphotographyforums.com/forums/showthread.php?t=1684 and I guess enough folk have been looking.

Best wishes,

Ray

Asher Kelman

December 15th, 2006, 10:46 AM

Asher,

As Ian mentioned, is that sensor dust or 60mph flies stuck to the lens?

I also alluded to the sky in a previous post. What did you use to convert the RAW file? The ACR conversion shows nice blue skies, as opposed to your purple ones.

Regards,

Stuart
Sorry Stuart for missing your post!

(I was taking a workshop on Leaf Aptus Backs! I'm now a certified Leaf Technician!)

The spots must be on the sensor. I have not cleaned the sensor and have not botheredhoot as I normally shoot much wider apertures. Out of a car, I wanted to get more depth and so those bugs are dirt on the sensor!

The sky color? I cant remember. I liked it. I didn't see purple. Is your monitor calibrated?

I'll recalibrate my Eizo and see how it is!

Asher

StuartRae

December 15th, 2006, 11:08 AM

Asher,

I liked your sky as well, but the red channel is significantly higher. Maybe "purple" is the wrong word, but have a look at these two crops from the top left corner.

ACR conversion RGB = 43:110:161

http://web.ukonline.co.uk/sw.rae/examples/ACR_Sky.jpg

Your version RGB = 105:116:168

http://web.ukonline.co.uk/sw.rae/examples/Leica_Sky.jpg

My monitor is as well calibrated as I can get it, but alas it's dying, and must soon be replaced.

Regards,

Stuart

Nathaniel Alpert

December 15th, 2006, 11:10 AM

I have been following this discussion with interest and some dismay. I wish to clarify some of the points that Bart van der Wolf and other have made.

van der Wolf wote "... I agree that AA-filtering is not a solution, but it is an attempt to prevent it from happening. Mathematically aliasing is an easy problem to prevent, just remove the highest spatial frequencies in the projected image before it hits the regularly spaced sensels. The catch is that it will reduce the resulting resolution by a factor of 2-3. Given that aliasing artifacts are not always as obvious as in the example shown in this thread, or they can sometimes be remedied rather easily after the fact, most of us are unwilling to pay the price of lost resolution just to be on the safe side."

There seems to be a rampant misconception, namely that one is "entitled to all" the resolution available from a given lens, independent of the properties of the sensor. But you really cannot go beyond the resolution limits imposed by the sampling of a digital sensor without corrupting the image. And do we really need to push the envelope? The 10-16 Mpixels sensors available today can provide excellent enlargements, better in some ways than can be achieved with 35 mm film. Adding a properly designed AA filter does not reduce the resolution by a factor of 2 to 3. I have never seen any evidence of that. Theories (and practice) in digital signal processing show that it is possible under somewhat idealized conditions to **exactly** reconstruct an analog signal from a finite number of digital samples, provided there is no information in the incoming signal that exceeds the Nyquist frequency of the detector. In terms of digital imaging it is only in those frequencies below Nyquist that one may gain an advantage with a good lens. (Some photographers use Leica lenses on the 1DsII for just that reason). One needs to consider the lens and sensor together when designing the system. I have not seen any evidence that the beloved Leica look now seen by digital adherents comes from the inclusion of information that exceeds the Nyquist frequency. My expectation is that whatever we are seeing comes from better performance at lower frequencies.

Imaging without an AA filter violates the no free lunch theorem. Mathematical analysis shows that it is not possible to remove the effects of undersampling (aliasing). The only valid way to obviate the AA filter is to make the sampling in the sensor so high that its Nyquist frequency exceeds the cut off of the lenses MTF. Probably, the current sensors are not that far from matching lens performance. Notice that no one dropped the AA filter with a 6 Mpixel camera. The aliasing would have been intolerable.

There will not be any practical antialiasing software. If we are lucky some mitigation may be found to disguise the harmful effects. Lieca surely understood the trade off imposed by a lack of AA filter. In certain scenes whose frequency content somehow just matches the properties of their sensor, you will get a little improvement. In all other cases their camera will perform less optimally than it would with a good AA filter. Leica photographers will just have to accept and adapt to this trade off.

I hope this post adds to rather than subtracts from the debate.

Asher Kelman

December 15th, 2006, 11:16 AM

Nathaniel Alpert

December 15th, 2006, 11:34 AM

How close to the sensor does an anti-aliasing filter have to be?

IOW, could one design such a filter in front of the lens? Oe else could one have a filter that popped down close to the sensor when you activated that "function"?

Asher

The object of the filter is to remove (image smoothing) higher frequencies. It could be part of the lens design, as you are in effect degrading the lens resolution.

James Roberts

December 15th, 2006, 11:44 AM

Nathaniel,

I actually agree with your statement that the obvious (to me, anyway) sharpness and detail improvement of the M8 over, say, a 1ds2, has to do with sensor performance unaffected by aliasing.

And I'm not sure, really, how Leica has designed any of the filtering that is on the camera--IR or AA, though I have little reason to doubt that you are correct theoretically speaking.

All I know is that--practically speaking--the shot as posted by Asher presents little real-world difficulty to print.

I've also just now started to see the combination of new M8 (new hardware and firmware) coupled with new ACR (in PS CS3 beta). So far, the combination is looking very good indeed!

Asher Kelman

December 15th, 2006, 12:17 PM

Thanks Jamie for the helpful and positive response.

I am as you know a strong admirer of the new M8. Still, I do find things and getting the moire minimized conveniently is needed.

I'll use CS3.

I also have newer images!

Asher

Asher Kelman

December 15th, 2006, 12:19 PM

Looking at your pictures on my apple monitor clearly shows what you are saying!

What can I say?

I have weird tastes!

AsherAsher,

I liked your sky as well, but the red channel is significantly higher. Maybe "purple" is the wrong word, but have a look at these two crops from the top left corner.

ACR conversion RGB = 43:110:161

http://web.ukonline.co.uk/sw.rae/examples/ACR_Sky.jpg

Your version RGB = 105:116:168

http://web.ukonline.co.uk/sw.rae/examples/Leica_Sky.jpg

My monitor is as well calibrated as I can get it, but alas it's dying, and must soon be replaced.

Regards,

Stuart

Asher Kelman

December 16th, 2006, 12:36 AM

I have another approach. I gave this issue to an imaging specialist who designs compression algorithms to see if he can get this issue solved mathematically.

Asher

John Sheehy

December 16th, 2006, 08:03 AM

There's some component that's related to the screen and magnification. Here, in PS with a 1280x1024 LCD at 33% it's very apparent, at 50% it almost vanishes and it comes back strongly at 66%. I'll be curious to see what happens on the 1600x1200 LCD.

LCDs are sharper than CRTs at the pixel level, so any aliasing is going to be more obvious.

As far as zoom percentages are concerned, many viewing/editing programs use nearest neighbor algorithm for some or all ratios, so the display will have additional aliasing beyond what the original has. 66% is a notoriously bad viewing resolution in Photoshop. I never use it.

The original in this case is full of aliasing and moire. All high-contrast edges have color fringing in the RAW. A shot like this should be shot at a very high f-stop, so diffraction will eliminate the alasing, IMO. For shallow DOF, you are stuck with aliasing unless you use some kind of filter that throws some photons off a little bit.

IMO, this is not a good design philosophy. A proper AA filter used with this camera would result in highly sharpenable RAWs. The sharper your lens is at the pixel level (and Leica lenses are very sharp), the more sharpenable the image is without sharpening noise. The non-noise-related sharpening artifacts would be no worse than the aliasing.

Asher Kelman

December 16th, 2006, 12:07 PM

John,

Could one design an external filter which would be exactly matched for f stop etc that one could slip in front of the lens of this particiular camera.

Asher

John Sheehy

December 16th, 2006, 03:16 PM

John,

Could one design an external filter which would be exactly matched for f stop etc that one could slip in front of the lens of this particiular camera.

You'd want something that would spread photons about 1/2 to one pixel width off course. I don't know if its possile to do correctly from the front threads. The best place for this is right over the sensor. :(

Have you tried high levels of caffeine?

Asher Kelman

December 16th, 2006, 04:17 PM

John, maybe I'm already over the caffeine limits! I can still move the camera exactly 0.6 pixels. I can't change the tremor to integers or half integers. :)

To the moire, I wonder whether poor subsampling technic from the data incoming from the chip might be responsible in part. I'll put online images taken under better conditions.

It seems that when any digital image files are encoded and then stored, data is discarded in uniform non-detail rich areas. So that is one place that the M8 CCD encoding could worsen the already present detail mismatch, (that the sensels are insufficent for the incoming detail). I am told that such subsampling could be improved.

One especially difficult area is the removal of moire when the repeating lines occur in more than one axis. In this image, there is an added issue, the lines are also converging.

Asher

James Roberts

December 17th, 2006, 07:27 AM

{snipped}
The original in this case is full of aliasing and moire. All high-contrast edges have color fringing in the RAW.
{snipped}
IMO, this is not a good design philosophy. A proper AA filter used with this camera would result in highly sharpenable RAWs. The sharper your lens is at the pixel level (and Leica lenses are very sharp), the more sharpenable the image is without sharpening noise. The non-noise-related sharpening artifacts would be no worse than the aliasing.

John, with all due respect, I am not seeing what you're evidently seeing. In C1, the "original RAW" is not full of aliasing. The high contrast edges DON'T have any colour fringing whatsoever.

They DO in ACR, so I can only think that they're not uncompressing the RAW file correctly. It's a 16 bit (actually 14 bit) image compressed to 8. As far as I know, Leica only worked with C1 on the M8.

(ACR 4 does work a lot better than ACR 3.x with the M8--it has a better set of controls--but it's still not as good as C1).

The only thing a C1 16 bit TIFF produces--at 100% in PS or in a print--is the colour "bleed" already reported. That may be a product of aliasing--absolutely--but it's not a bad problem at all.

Even the 1ds2 displays moire under certain circumstances, and IMO the M8 is sharper, and (I'm going to get flamed for this) produces as good or better enlargements in print (which is saying something given the smaller size of the sensor).

James Roberts

December 18th, 2006, 02:20 PM

Ok, my point about Asher's photo was that the color fringing I was seeing in a print was minimal, and that all cameras have moire to some degree...not that the post Asher posted didn't have artifacts.

So in the interest of full disclosure, have a look here at this thread on the LUF talking about moire and showing some "good examples" of "bad moire" from things like rooftops.

http://www.leica-camera-user.com/digital-forum/11763-have-look-m8-image.html

Note that I haven't seen these at 100%, but they look more typically--and more severly--flawed to me than Asher's shot.

Note, too, that there's a link at the bottom of the thread to the 5d doing the same sorts of things, and it certainly has an AA filter :)

Asher Kelman

December 18th, 2006, 03:10 PM

Does anyone have pre-release M8 files which I hear were 16 BIT? I'd like some moire examples to analyse.

Also Anyone have M8 files with no sub-sampling from a very early Leica test bed?

Asher

James Roberts

December 18th, 2006, 04:16 PM

Does anyone have pre-release M8 files which I hear were 16 BIT? I'd like some moire examples to analyse.

Also Anyone have M8 files with no sub-sampling from a very early Leica test bed?

Asher

Asher, three quick thoughts...

First, the M8 shots today are compressed to 8 bits, with a maximum loss of 2 bits (if I understand the compression algorithm) and so uncompressed are about 14 bits (essentially the same as the DMR). This allows Leica to claim they are, in fact, 16 bit RAWs.

Secondly, I've heard through a pretty reliable source that a nearly-done level of firmware will let you turn off the compression, and get a DMR-like DNG. Personally, the difference between consistently large (20MB) and slow to work with DNGs and the new M8 ones are so great that if I could compress my DMR files in the same way I most certainly would!

Last--what do you mean by sub-sampling?

Asher Kelman

December 18th, 2006, 04:28 PM

Jamie,

We may have a new compression utility available. I just want to be able to look at very primitve Lecia image files even before any data is compromised to make the DNG.

Anyway, I'm very happy with the M8, even like the noise at high ISO! Has a painterly feeling!

Subsampling: going from the digital conversion data set from the chip to the RAW file involves a lot of sampling decisions and deciding what to keep. Id like an software designer to try and put his hand to these primitive files before the anything else is done.

Asher

John Sheehy

December 19th, 2006, 10:17 PM

Asher, three quick thoughts...

First, the M8 shots today are compressed to 8 bits, with a maximum loss of 2 bits (if I understand the compression algorithm) and so uncompressed are about 14 bits (essentially the same as the DMR). This allows Leica to claim they are, in fact, 16 bit RAWs.

The only "compression" used is gamma. The highlights, therefore, are a bit lossy, but the deepest shadows could hypothetically contain far more depth than a 12- or 16-bit linear RAW.

Asher Kelman

December 19th, 2006, 10:34 PM

John, could you expand on that? The shadows.

Asher

John Sheehy

December 21st, 2006, 06:47 PM

John, could you expand on that? The shadows.

It's what the values represent.

For 12-bit linear, you have 0, 1/4095, 2/4095, 3/4095, etc. Actually, most cameras don't have 4096 levels, but something around 3500 - 4000.

For 8-bit data with 2.2 gamma, the values, when converted to linear, are 1^2.2/255^2.2, 2^2.2/255^2.2, 3^2.2/255^2.2, etc. Translated to 1/4095ths, they come out to be 0.021/4095, 0.096/4095, and 0.233/4095. You pay for it at the highlight end, where the three highest 8-bit values represent 4025/4095, 4060/4095, and 4095/4095.

I spoke too soon about 16-bit linear in a previous post; 8-bit gamma 2.2 is only very slightly advantageous for the deepest shadows, and only has a couple levels lower than 16-bit's "1".

Nat Burgess

April 11th, 2007, 09:57 AM

Moire or none, this picture screams "road trip." Did you have babies in need of a diaper change in the back seat when you took it? Or a **** art student in search of an adventure? When I see a good picture of an abandoned house I feel nostalgic for my childhood home, because in a child's mind it could be inhabited only by me - or nobody. And I love pictures taken from the driver's seat, because they remind me of road trips I have taken - and hope to take. Fitzgerald said we are borne "like boats against the current, ceaslessly into our own past" (or something like that; I don't have a Bartlett's handy), but I want to see more pictures that promise a trip with the current, into something new. Leave the house to buy a tomato and return three days later with a headache, a sunburn, and new friends in three states. That's what I'm talking about. Oops - time to change a diaper.