Re: Re[3]: filmscanners: Film Scanners and what they see.
Remember, aliasing is when two or more different input signals appear identical at the output of a sampled system. This only happens when the input signal exceeds the Nyquist limit of the sampled system. I've just twigged that you and others are only thinking in the frequency domain, without considering what happens to the luminance and colour components of high frequency info. No wonder this one has run and run... Carrying out the aliasing upstream, via a filter or defocussing, does not remove these - you input a blurry image which avoids the Nyquist limit, but pixel values will still be aliased, still be different to the original image. You've just done the integration of colour and luminance components in a different place. Regards Tony Sleep http://www.halftone.co.uk - Online portfolio exhibit; + film scanner info comparisons
Re: Re[3]: filmscanners: Film Scanners and what they see.
Basically, I'm trying to say that scanner softness has many causes but the inherent reason is not related to aliasing at all. It is the from low pass filtering due to the individual CCD cell. Fundamental disagreement about the 'not related' bit here. How are filter characteristics independent of aliasing in the image, in a CCD scanner? In fact, I'm aware of empirical studies showing that introducing aliasing into a non-aliased system actually INCREASES apparent sharpness (to a point). Apparently the eye perceives the increased "grain" as more sharp than the smoother non-aliased image. This seems plausible, since the eye will latch onto grain boundaries as image boundaries - in analogue, to an extent fast grainy film disguises lack of optical sharpness for the same reason, compared to fine-grained materials, despite the higher resolution of the latter. Adjacency effects produce apparent sharpness. Aliasing certainly occurs in a scanner when the ARRAY BANDWIDTH is insufficient for the sampled signal. In this case, the effect Tony has quoted in his Kodak reference applies. The visible effect of aliasing is increased "apparent grain" in the image and not "softness". Not so. What we see in aliasing with slow, fine grained films is averaged pixel values and loss of image boundary information = softness. There is no enhancement of grain, unless you want to start calling pixels grain. Grain is invisible to each pixel, each can only aggregate the luminance of what it sees, which may be 1.9grains or 0.001 grains, or 50 grains 0.1-0.5 of a pixel across. Or whatever. Only once grain size enters the picture (sic) as information which is close to the CCD bandpass characteristic, the Nyquist limit, will one begin to see enhanced grain. If you'd said 'degraded or coarsened tonality', I'd agree with that. Regards Tony Sleep http://www.halftone.co.uk - Online portfolio exhibit; + film scanner info comparisons
Re: Re[3]: filmscanners: Film Scanners and what they see.
Tony Sleep [EMAIL PROTECTED] wrote: I'm not going to try and explain this properly without graphics, as (heck, is that the time) I have work to do, and it will be instantly obvious what the problem is from a web page I am working on. Speaking of web pages, I just modified my scanning page, and I'd appreciate feedback. I've added a graphic as both a jpg and png which demonstrates aliasing on a regular pattern - an offset printed image. Hopefully it is a useful analogue of what happens when a scanner scans film, bearing in mind that grain is random. Please check out the page - go to http://wordweb.com and click on the "scanning" link in the menu. BTW the resampling also demonstrates something I tried to explain in an earlier discussion about aliasing with offset printed images - while the 600dpi image resampled smaller look smoother, it is significantly less sharp than the 75dpi image, and the colours are less accurate. Thanks in advance for any feedback! Rob
Re: Re[3]: filmscanners: Film Scanners and what they see.
- Original Message - From: "Tony Sleep" [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Monday, December 04, 2000 11:45 PM Subject: Re: Re[3]: filmscanners: Film Scanners and what they see. The visible effect of aliasing is increased "apparent grain" in the image and not "softness". If you'd said 'degraded or coarsened tonality', I'd agree with that. I was just using Rob's words. Your words are fine too. We're all saying the same thing. It is an increase in "apparent" grain not actual grain. Degraded or coarsened tonality works for me too. Byron
Re: Re[3]: filmscanners: Film Scanners and what they see.
- Original Message - From: "Tony Sleep" [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Tuesday, December 05, 2000 6:28 AM Subject: Re: Re[3]: filmscanners: Film Scanners and what they see. 1) Defocus the input signal. 2) Optically filter the input signal. Those are 'cheating'! No, not cheating. Remember, aliasing is when two or more different input signals appear identical at the output of a sampled system. This only happens when the input signal exceeds the Nyquist limit of the sampled system. So given this, it should be clear that items #1 and #2 are NOT cheating. Instead, they go directly at the heart of the matter. They filter the input signal so it will not alias when sampled by the CCD array. In fact, this is precisely what true anti-aliasing filters are all about. 1) Is aliasing always present in a scanner? You say yes, I say no. Put it this way, I have yet to see a CCD scan which doesn't exhibit aliasing. Aliasing seems to me to be an intrinsic property of CCD's. Though I agree there are things you can do to try and hide, cancel or obliterate the artifacts. Your point (4) above is intriguing here, though: plainly if the Nyquist limit is more flexible than I thought, I am wrong, and aliasing is commensurately flexible too. There are actually two key points. 1) The Nyquist limit of the array is flexible by array design, and 2) The signal bandwidth sampled by the array can be modified independantly as mentioned in items #1, #2, and #3 of my previous post. These two factors mean that proper aliasing control is similarly flexible. For example, item #3 and #4 can be combined. Just set a given cell size/shape, calculate the cells upper bandwith limit, and then design an array to sample at twice that rate. Square cells that are side by side (touching) in an array fail this criteria since the resulting array's Nyquist limit is about half the individual cells bandwidth -- no good -- aliasing results. If the cells were made smaller but the center to center spacing kept the same (ie dead space in between) the problem would get worse since the array sampling rate hasn't changed but the individual cells bandlimit has increased (due to a smaller cell size). Conversely, if the cell size is doubled and the array is still sampled at the original rate (ie staggered arrays) then success -- no aliasing. Also the cell shape could be changed away from square with different bandwidth limits and different side-lobe behaviour. Since we have problems with basic linear system theory I'm certainly NOT getting into that aspect !!! Anyway, the optimum shape is a study of its own. 2) Does an individual CCD cell bandlimit the signal based on its size and geometry? I say yes, you say...??? (I can't tell...you seem to ignore this point) I say, have said, YES, the filter is the Nyquist limit, which arises in pixel size and geometry, and aliasing is the consequence of the filtering. That is why I regard the two as inextricably linked properties of CCD's, notwithstanding anti-aliasing techniques which can be subsequently deployed to mitigate the effect. I think this is the fundamental point of misunderstanding. The individual cells bandwidth limit is NOT the same thing as the arrays bandwidth limit (ie Nyquist). As mentioned earlier, items #1, #2, #3 affect the output from the individual element and are unaffected by Nyquist. Only the sampling rate affects the arrays filter limit (ie Nyquist). The designer is free to twiddle each independently. Anyway, I'm running out of steam. Hopefully this clarifies rather than muddies... Maybe someone else with better explaining skills can take up the challenge. Byron
Re: Re[3]: filmscanners: Film Scanners and what they see.
Craig W. Shier [EMAIL PROTECTED] wrote: physically implementable scanner. If the sample areas are sufficiently samll. i.e. if they do not overlap, there will be no reduction in sharpness for a sufficiently high resolution scan. For example, if your lens resolves 50 lppm, a 2540 dpi scan is theoretically good enough to reconstruct the original image. (Realistically though 2 or three times that would improve the reconstruction.) Craig, I like your explanation, but it doesn't take into account the interference between the grain (or dye cloud patterns) in the film and the scan resolution, which seems to be the main source of pain in film scanning. When the grain is taken into account, it's the relationship between the grain (or dye clouds, whatever) and the pixel size which is the most important factor, not the resolution of the camera's lens system. Tony could probably point out other limiting factors, but in my (albeit limited) experience in film scanning, the main problem is interference between the frequency of samples and the random variations in dye clouds that are the most significant - and it's certainly aliasing as I understand the term. If the patterns were regular you would get moire, but the patterns are random. Rob
Re: Re[3]: filmscanners: Film Scanners and what they see.
Filtering is not aliasing. Agreed. But ... Furthermore, aliasing doesn't occur in the continuous domain. And that is where the effect I described occurs. It's a physical fact of CCD's, the mismatch between sub-Nyquist target detail and pixel size. The Nyquist limit is the filter, and aliasing is what results, in the scan. The inherent softness from a scanner has nothing to do with aliasing. It is simply regular, everyday, good old fashioned filtering from the CCD cell. The individual cell low pass filters the signal and the result is softness. It really isn't any more esoteric than that. Whatever happened to Occam's razor? You are needlessly multiplying entities here. For the purpose of analysis it is may be worthwhile to regard filtering and aliasing as separate, but in the CCD they are inseparable manifestations of the same thing: Nyquist. You can't have a CCD with any finite pixel size which doesn't filter and display aliasing artifacts in direct relation. If you can find a way, you'll be a very rich man. One can design a scanner that doesn't have aliasing and they will find it still has the softness. This is highly disingenuous, and you know it! An analogue PMT scanner avoids aliasing and retains the softness simply because it doesn't write pixels, there is no Nyquist limit in the analogue domain. Its softness has different origins, the size of the scanning spot limits resolution, the familiar old-fashioned 'circle of confusion' optical limit to sharpness. As soon as you stick an ADC on the output, you'll get aliasing. It won't arise in quite the same way as with as CCD - where filtering/aliasing are a hard-wired fact of life - but will fall out of the sampling rate of the ADC itself. You cannot design a scanner which outputs pixel values which does not exhibit aliasing without cheating. You can certainly process the signal to try and remove aliasing artefacts, but not undo the filtering which caused them. However this is downstream of the CCD and in the realm of signal processing. Anti-aliasing is deployed in many scanners and digicams, which ought to be a clue about what the designers think they are trying to deal with and what they think it is called. The whole aliasing argument in this context is based on a fundamental misunderstanding of aliasing AND basic filter theory as far as I can tell. But who knows, maybe I'm missing something brilliant. The Kodak description is precise and means what it says. Considering filtering and aliasing as separate entities, not linked in any way, is spurious in the context of where this discussion started from : why CCD scans are not sharp. Since you think you disagree, and this thread is getting increasingly obscure and muddled, let's try and redefine terms:- (1)CCD sampling applies a low pass filter to image detail - and - (2)that filtering causes artefacts in scans (jaggies, softness, averaging of pixel luminance values, false colour across pixel groups) - and - (3)the terminology for (1)+(2) = 'aliasing' in scanning. I suspect (3) will come as a semantic surprise to you and maybe a few others, perhaps coming at aliasing from an electronics or similar background where it's customary to separate filtering and aliasing as they are distinct parameters. Nevertheless, it's the customary use in digital imaging for what we see, and why, when asked about softness in scans, I said 'aliasing'. In a CCD, that one word is used to describe the process whereby a class of artifacts arise because a CCD is an array wherein filtering and aliasing are fixed, hardwired and entirely interrelated consequences of pixel size. The thing that does the filtering is the CCD, what is produces is aliased. The Kodak definition sums this up quite nicely, it's not just me making it up to upset you and Austin. Deconstructing the process for which 'aliasing' is shorthand, I still don't think any of us are saying anything different. Who would believe a one-word response could cause all this!? Hopefully, someone somewhere now has a slightly better idea why scans are a bit soft. g Regards Tony Sleep http://www.halftone.co.uk - Online portfolio exhibit; + film scanner info comparisons
Re: Re[3]: filmscanners: Film Scanners and what they see.
Bottom line. Fuzziness of a scan is caused by two things, a) sampling error and b) correlation. Thanks for all that. It seems to confirm the etymological origins of WW3 :) Regards Tony Sleep http://www.halftone.co.uk - Online portfolio exhibit; + film scanner info comparisons
Re: Re[3]: filmscanners: Film Scanners and what they see.
Byron am I right in understanding that you're saying aliasing does *not* cause scanner image softness. On the other hand you *aren't* saying that the enhancing of apparent grain caused by the interference between scanner resolution and film grain (dye cloud patterns) - is something other than aliasing? No, he's setting hares running in all directions for the sake of an argument:) Image frequency filtering is an intrinsic property of the CCD, aliasing its intrinsic manifestation in the resulting image. The whole of the argument seems to devolve from my answering a question 'what causes softness in scans?' with the word 'aliasing'. Byron, Austin etc see this as Sophistry, since one can conceptually separate the filtering (mechanism) from the aliasing (result). Plainly, they argue, aliasing - being a result - cannot be a cause. Pedantically they are correct, but the rest of the world has been referring to this species of image artifact as aliasing for as long as I can remember. Aliased scans are soft scans, and we can't escape them in CCD scanners without anti-aliasing jiggery-pokery (interpolation techniques). Please make your own mind up whether you think it was a reasonable use of the 'a-' word. :-) Regards Tony Sleep http://www.halftone.co.uk - Online portfolio exhibit; + film scanner info comparisons
Re: Re[3]: filmscanners: Film Scanners and what they see.
Craig, I like your explanation, but it doesn't take into account the interference between the grain (or dye cloud patterns) in the film and the scan resolution, which seems to be the main source of pain in film scanning. When the grain is taken into account, it's the relationship between the grain (or dye clouds, whatever) and the pixel size which is the most important factor, not the resolution of the camera's lens system. You get can plenty of grain aliasing with monochrome films, especially fast, silver-based BW negs. The metallic grains are large and have sharp boundaries which kicks it off a treat, provided the scanner optics are able to resolve them. The scanner neither knows nor cares what is image detail and what is grain topology, of course. In areas of even tone, size of grains will be roughly similar, and distribution not entirely random - there'll be an average distance between them and bell-curve deviation from that. So there will be an interference effect which will be a product of grain distribution and CCD element distribution, albeit weakened by the deviation of the former. Colour aliasing adds an extra dimension, since it arises not only in the response of single pixels, but how the RGB group interprets colour when presented with boundaries which it cannot resolve. It can only fudge the colour values of each grain. Where grains of different colour coincide or overlap some, the RGB group can only aggregate the colours. This is bound to lead to false colour - remember each of the R, G and B CCD pixels has a filtered monochromatic response, they are blind to complementary components. I'm not going to try and explain this properly without graphics, as (heck, is that the time) I have work to do, and it will be instantly obvious what the problem is from a web page I am working on. Regards Tony Sleep http://www.halftone.co.uk - Online portfolio exhibit; + film scanner info comparisons
Re: Re[3]: filmscanners: Film Scanners and what they see.
- Original Message - From: "Rob Geraghty" [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Monday, December 04, 2000 3:57 AM Subject: Re: Re[3]: filmscanners: Film Scanners and what they see. bjs [EMAIL PROTECTED] wrote: One can design a scanner that doesn't have aliasing and they will find it still has the softness. The whole aliasing argument in this context is based on a fundamental misunderstanding of aliasing AND basic filter theory as far as I can tell. Maybe now I'm seeing why this thread has persisted. Byron am I right in understanding that you're saying aliasing does *not* cause scanner image softness. Yes. On the other hand you *aren't* saying that the enhancing of apparent grain caused by the interference between scanner resolution and film grain (dye cloud patterns) - is something other than aliasing? Agree. Turning the last point around - do you agree that the enhancement of apparent grain caused by the interference between scanner resolution and film grain *is* aliasing? Yes. Basically, I'm trying to say that scanner softness has many causes but the inherent reason is not related to aliasing at all It is the from low pass filtering due to the individual CCD cell.In fact, I'm aware of empirical studies showing that introducing aliasing into a non-aliased system actually INCREASES apparent sharpness (to a point). Apparently the eye perceives the increased "grain" as more sharp than the smoother non-aliased image. Aliasing certainly occurs in a scanner when the ARRAY BANDWIDTH is insufficient for the sampled signal. In this case, the effect Tony has quoted in his Kodak reference applies. The visible effect of aliasing is increased "apparent grain" in the image and not "softness". Sigh, Byron
Re: Re[3]: filmscanners: Film Scanners and what they see.
Craig wrote: Good point. I haven't heard the interference you refer to called aliasing (although apparently it has been done)and I've not heard a really good technical explanation of this effect. Pete (photoscientia) has a good explanation on his web site. I first saw this kind of aliasing years ago when I started using flatbed scanners. I found that scanning an offset printed photograph in a magazine at more than 100dpi was a waste of time because at the higher resolutions I tried (up to 300dpi) the quality of the image got *worse* due to interference between the scanner resolution and the offset dot pattern. This interference also exists when scanning film, but as I mentioned - the grain or dye pattern is random so the interference isn't an obvious moire pattern. However, it seems to be caused by diffraction of the scanner's light source by the dye clouds in the film. This has the effect of increasing the area sampled by the scanner and reducing sharpness (or alternatively increasing the apparent size of small artifacts i.e. grain). A higher sampling frequency would not necessarily diminish this effect as it is a function of the light beam and not the sampling device itself. Interesting theory, but I don't think it's the main problem as I understand it. See my offset printing example above - a *reflective* medium which demonstrates the same problem. The scanner CCD is seeing the edges of dot patterns, and as a result not getting accurate results. If the scanning resolution is high enough, the scanner should see the offset dots themselves not the edges - or in the case of film, the dye clouds not their edges. So as it's not quite the same as either aliasing effect I described previously, this may be a third definition. I don't think it's any other definition of aliasing. It's a noise effect caused by the sampling frequency not being high enough. Just the same as the distortions in sound if it's recorded with too low a sample rate. However, as I hopefully sorted out with Byron, aliasing is NOT the cause of scanner image softness. It's the cause of increased apparent grain and as Tony mentioned, colour distortions. Regards, Rob Rob Geraghty [EMAIL PROTECTED] http://wordweb.com
Re: Re[3]: filmscanners: Film Scanners and what they see.
Austin Franklin [EMAIL PROTECTED] wrote: Interesting! Is aliasing THE reason why scanning loses some sharpness. What do you think aliasing is? I am curious what you base your claim above on, and I do not believe it is a correct statement. In my experience with the LS30, aliasing doesn't reduce sharpness. It increases the apparent grain. Rob
Re: Re[3]: filmscanners: Film Scanners and what they see.
on 3/12/00 2:08 am, bjs at [EMAIL PROTECTED] wrote: The most fundamental reason that scanners lose sharpness is because they are area samplers rather than point samplers. This is a physical necessity due to the finite size of each CCD cell. The resulting area integration of each sample forms a physical low pass filter which softens the image. Aliasing isn't relevant to this question. But, er, what you just described *is* aliasing. Hate to contradict the listmom but... hell, no, it ain't. This is my understanding of aliasing. Others will jump all over me, and please do, but I think it shows why the above is wrong. Aliasing occurs when a signal is sampled at a frequency too low to capture the frequency being sampled. Done like this it appears (aliases) to be a signal of a lower frequency (I seem to remember that the alias frequency is the *difference* between the signal and the sampling frequency). Its effect is likely to be *strongest* with point sampling. The most obvious example of this is a cart wheel in a western which appears to go backwards... you can think of this as a high frequency signal (the rate at which the spokes pass, say, 12 o'clock) which is being sampled at a low frequency (24 fps). Because the sampling frequency is so low the frequency (rotation speed) of the wheel is 'aliased' to another frequency... so that it appears to go slowly forwards, backwards, stop etc. This is a special case I know and technically there are a few things wrong with the example, but at least the effect is clear and familiar. If you shot the wheel with a high speed camera (say 240 fps) you would capture the true motion of the wheel. A moire pattern is (I think) a visual form of aliasing. This occurs typically when a high frequency visual signal (say a dot screen in newsprint) is scanned at too low a resolution. As a result, rather than showing the true frequency you get banding at another frequency which represents the interaction between the scanning resolution and the resolution of the dot screen. -- Johnny Deadman http://www.pinkheadedbug.com
Re: Re[3]: filmscanners: Film Scanners and what they see.
Uh no, it is not aliasing. Not even in the slightest. The physical cell simply acts as low pass filter due to its size and geometry. Mathematically it is the 2 dimensional convolution of the cell's structure with an idealised point sampler. NONE of this causes ANY aliasing to occur but the damage (in terms of softness) has already been done. That *is* aliasing. I suggest you look it up in a reference book before obfuscating this further. Here's a terse version from Kodak's dictionary of digital imaging terms - http://www.kodak.com/US/en/digital/dlc/book4/chapter2/index.shtml "Aliasing An effect caused by sampling an image (or signal) at too low a rate. It makes rapid change (high texture) areas of an image appear as a slow change in the sample image. Once aliasing occurs, there is no way to accurately reproduce the original image from the sampled image." Regards Tony Sleep http://www.halftone.co.uk - Online portfolio exhibit; + film scanner info comparisons
Re: Re[3]: filmscanners: Film Scanners and what they see.
Both phenomena depend on the use of a grid. But while aliasing is exemplified by forcing a pixel to be all one color (a binary sort if thing), the low pass effect has to do with diffraction That is *colour* aliasing, which is a special case of aliasing in general (luminance). You don't need to resort to esoteric stuff like diffraction, both arise because the pixel is unable to record anything except average colour and luminance. Colour aliasing involves the RGB pixel-group's response to colour, as well as the individual pixels, but fundamentally it's the same thing. Regards Tony Sleep http://www.halftone.co.uk - Online portfolio exhibit; + film scanner info comparisons
RE: Re[3]: filmscanners: Film Scanners and what they see.
Here's a terse version from Kodak's dictionary of digital imaging terms - "Aliasing An effect caused by... Be careful here. Aliasing may be the effect that is caused by...but that does not make that the definition of aliasing. Sorry to sound so obtuse here, but a severed limb is an effect caused by a mishandled chain saw, that does not make the definition of a severed limb "the effect caused by a mishandled chainsaw".
Re: Re[3]: filmscanners: Film Scanners and what they see.
- Original Message - From: "Tony Sleep" [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Sunday, December 03, 2000 10:15 AM Subject: Re: Re[3]: filmscanners: Film Scanners and what they see. Uh no, it is not aliasing. Not even in the slightest. The physical cell simply acts as low pass filter due to its size and geometry. That *is* aliasing. I suggest you look it up in a reference book before obfuscating this further. Filtering is not aliasing. Furthermore, aliasing doesn't occur in the continuous domain. And that is where the effect I described occurs. The inherent softness from a scanner has nothing to do with aliasing. It is simply regular, everyday, good old fashioned filtering from the CCD cell. The individual cell low pass filters the signal and the result is softness. It really isn't any more esoteric than that. One can design a scanner that doesn't have aliasing and they will find it still has the softness. The whole aliasing argument in this context is based on a fundamental misunderstanding of aliasing AND basic filter theory as far as I can tell. But who knows, maybe I'm missing something brilliant. Byron
Re: Re[3]: filmscanners: Film Scanners and what they see.
Tony is right here but just so we all understand each other: There are two valid uses of the term aliasing I have come across in my experience in signal processing and human machine interface development which are technically correct in context but mean very different things. The signal processing definition is an ambiguity or distortion in reconstructing an analog signal from a digital signal which was sampled slower than twice the highest frequency in the original analog signal. In scanner world this would cause ghosting if you tried to recreate a highly detailed silver based image from a coarse scan. We don't normally attempt such things. In the HMI world, aliasing refers to the jagged edges created by drawing a straight line segment on a raster display. In reality and in signal processing terms this is just sampling error (also known as digitization error) as an earlier poster indicated. But, the term "aliasing" has stuck for some time so it's not worthwhile to fight it. The terminology has migrated to the scanning world. Unfortunately if folk understood that it is really sampling error it would be less mysterious. As someone else already pointed out, sampling an image requires more than an infinitesimal point in a physically implementable scanner. If the sample areas are sufficiently samll. i.e. if they do not overlap, there will be no reduction in sharpness for a sufficiently high resolution scan. For example, if your lens resolves 50 lppm, a 2540 dpi scan is theoretically good enough to reconstruct the original image. (Realistically though 2 or three times that would improve the reconstruction.) In this case the sample area needs to be less than 1/2540 inch. If however the real size of the sample is 1/1500 inch, there is an overlap of samples called correlation. If your software knew exactly the size of the real sample area, you could still reconstruct the original but, since you don't know, you get a blurred image. (Note, the manufacturer knows and may incorporate some fancy software to help out but I don't know it they do or not.) Bottom line. Fuzziness of a scan is caused by two things, a) sampling error and b) correlation. --- Tony Sleep [EMAIL PROTECTED] wrote: Hate to contradict the listmom but... hell, no, it ain't. This is my understanding of aliasing. Others will jump all over me, and please do, but I think it shows why the above is wrong. Aliasing occurs when a signal is sampled at a frequency too low to capture the frequency being sampled. You're welcome to disagree with me, I'm as daft as anyone else. But we now have 3 people saying the exact same thing, yet managing to think they aren't and wanting to argue about it! As far as I can see, we agree exactly. Byron (bjs1) wants to call it something else other than aliasing, but what we've all described is aliasing and is called aliasing in scannerdom. Probably this gratuitous confusion is arising because people are coming at it from different backgrounds and simply not recognising the commonality. PS You're right about Moire, too. Regards Tony Sleep http://www.halftone.co.uk - Online portfolio exhibit; + film scanner info comparisons = Craig W. Shier [EMAIL PROTECTED] http://members.tripod.com/~rigmarole __ Do You Yahoo!? Yahoo! Shopping - Thousands of Stores. Millions of Products. http://shopping.yahoo.com/
Re: Re[3]: filmscanners: Film Scanners and what they see.
- Original Message - From: "Tony Sleep" [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Friday, December 01, 2000 5:16 PM Subject: Re: Re[3]: filmscanners: Film Scanners and what they see. Interesting! Is aliasing THE reason why scanning loses some sharpness. Or are there others? Charge-bleeding between pixels is another factor. Optical sharpness and flare, as with any lens apparatus. The most fundamental reason that scanners lose sharpness is because they are area samplers rather than point samplers. This is a physical necessity due to the finite size of each CCD cell. The resulting area integration of each sample forms a physical low pass filter which softens the image. Aliasing isn't relevant to this question. Cheers, Byron
Re: Re[3]: filmscanners: Film Scanners and what they see.
- Original Message - From: "Tony Sleep" [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Friday, December 01, 2000 5:16 PM Subject: Re: Re[3]: filmscanners: Film Scanners and what they see. Interesting! Is aliasing THE reason why scanning loses some sharpness. Or are there others? Charge-bleeding between pixels is another factor. Optical sharpness and flare, as with any lens apparatus. The most fundamental reason that scanners lose sharpness is because they are area samplers rather than point samplers. This is a physical necessity due to the finite size of each CCD cell. The resulting area integration of each sample forms a physical low pass filter which softens the image. Aliasing isn't relevant to this question. Cheers, Byron
Re: Re[3]: filmscanners: Film Scanners and what they see.
The most fundamental reason that scanners lose sharpness is because they are area samplers rather than point samplers. This is a physical necessity due to the finite size of each CCD cell. The resulting area integration of each sample forms a physical low pass filter which softens the image. Aliasing isn't relevant to this question. But, er, what you just described *is* aliasing. Regards Tony Sleep http://www.halftone.co.uk - Online portfolio exhibit; + film scanner info comparisons
Re: Re[3]: filmscanners: Film Scanners and what they see.
- Original Message - From: "Tony Sleep" [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Saturday, December 02, 2000 6:16 PM Subject: Re: Re[3]: filmscanners: Film Scanners and what they see. The most fundamental reason that scanners lose sharpness is because they are area samplers rather than point samplers. This is a physical necessity due to the finite size of each CCD cell. The resulting area integration of each sample forms a physical low pass filter which softens the image. Aliasing isn't relevant to this question. But, er, what you just described *is* aliasing. Uh no, it is not aliasing. Not even in the slightest. The physical cell simply acts as low pass filter due to its size and geometry. Mathematically it is the 2 dimensional convolution of the cell's structure with an idealised point sampler. NONE of this causes ANY aliasing to occur but the damage (in terms of softness) has already been done. Byron
RE: Re[3]: filmscanners: Film Scanners and what they see.
Interesting! Is aliasing THE reason why scanning loses some sharpness. What do you think aliasing is? I am curious what you base your claim above on, and I do not believe it is a correct statement.
RE: Re[3]: filmscanners: Film Scanners and what they see.
Weird - I just received truncated messages from the list (they're empty). Any ideas, Tony? Unfortunately not, though I have noticed them as well:( Run as it is now, via a remote listserver, I have no more insight than anyone else except for a few admin commands I have to send by email. I have to take problems up with my ISP. Regards Tony Sleep http://www.halftone.co.uk - Online portfolio exhibit; + film scanner info comparisons
RE: Re[3]: filmscanners: Film Scanners and what they see.
I did also; and they all appeared to be coming from Tony or in response to messages from Tony. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Rob Geraghty Sent: Thursday, November 30, 2000 1:08 AM To: [EMAIL PROTECTED] Subject: RE: Re[3]: filmscanners: Film Scanners and what they see. Weird - I just received truncated messages from the list (they're empty). Any ideas, Tony? -- Original Message -- Rob Geraghty [EMAIL PROTECTED] http://wordweb.com
Re: Re[3]: filmscanners: Film Scanners and what they see.
- Original Message - From: "Tony Sleep" [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Wednesday, November 29, 2000 12:25 PM Subject: Re[3]: filmscanners: Film Scanners and what they see. And with what I have I should be able to get the LS-30 to produce a scan that is in focus. However if you are doing this and scans are plainly out of focus although you have AF turned on, it's possible the scanner is busted. Out of focus LS30 scans are quite common on my friends machine. And I've encountered it many times on other LS30's so they must have some kind of problem in this area. So out of focus scans don't necessarily mean it is busted...just try again with your fingers crossed...it eventually seems to work. Byron
