Super-VHS however has some promise.
http://www.wired.com/news/technology/0,1282,41045,00.html
cheers Peter
Laserdisc, VHS, Super VHS, and other analog formats do not have "pixels", so speaking of the aspect ratio of "pixels" is inappropriate in those cases. These formats have 480 (or 483 as some sources say) visible scan lines, and what varies, resolution-wise, is the amount of information that can be encoded on each scan line based on the bandwidth limitations of the media and/or recording and playback devices.
While the 480 scan lines are interlaced, all of the sources mentioned above could be run through a line doubler which could take advantage of the 3:2 pulldown method of recording movies on those media and get the full 480 scan lines of information wihtout the scan line overlap that causes some apparent loss of resolution. Therefore, all of the resolution figures for all these media should be something by 480, unless some format doesn't actually encode all the scan lines (CDi?)?
Another consideration when comparing formats is whether the format is composite or whether the color and brightness information are stored separately without interference. DVD and S-VHS store color and brightness separately, meaning that if an S-Video cable is used, the artifacts created by separating those elements in a composite signal can be avoided. VHS actually stores color and brightness separately, but only S-VHS players tend to have S-Video outs, and the color and brightness signals interfere on VHS (a problem solved by moving the luminace signal to a higher frequency carrier for S-VHS). Laserdisc is composite, meaning that those elements must be separated, so that those artifacts are unavoidable. (Use S-Video cable with laserdisc if laserdisc player hgas better comb filter, and use composite cable if TV has better comb filter). With DVD or S-VHS, use an S-Video cable, always (or component with DVD if possible).
There is more to the comparisons than simple resolution comparisons. If a format came out that had a 1024x480 resolution, but was composite, DVD's component encoding at 720x480 would likely produce a better picture.
Then there's the color portion of the signal. What is the bandwidth of the color signal in each format? Resulution figures quoted are typically for the luminance portion. See how many alternating fully saturated, full luminance red and black transitions you can record on a scan line on plain VHS.
DVD is clearly the winner, with 720x480 resolution. Comparing Laserdisc with S-VHS is a bit trickier, though. There is more to the comparison than meets the eye.
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Evans A Criswell
Huntsville-Decatur Movie Theatre Info Site
As far as DVD is concerned, it really depends on the player. I have a Pioneer player that plays LDs, CDs and DVDs. You can see tons of artifacts on the DVDs!!! But take the same DVD and pop it into the Mac and I see very few compression artifacts.
Tape wears out. It does not last as long as magneto-optical media. If I record something important, I want to be able to store it forever without having to transfer it onto a new tape when the old one wants to go. And it decays even faster if I watch the tape over and over and over and neglect to store it fully wound and vertically.
It will be nice to be able to play our old tapes on new HDTVs with ease, and I'll probably get a unit more for time-shifting than archiving. I want a real archiving media, damn it! MPEG2 is NOT good enough for that. Even Evans should agree with that. DV compression is better than DVD compression. DV compresses each frame individually, whereas DVD does not. DVD also has more artifacts. Unfortunately both are limited to NTSC resolution for right now.
Also, ever wonder whats in store for the next gen of TiVo's? Click here
-Jonathan
Put another way if the information that makes up a 35mm film could be scanned at a very high resolution and then digitally compressed it might be possible to store this in a format on super-8 film.
Just don't ask me how. Something more complicated than amorphic lenses is needed methinks.
cheers Peter
And whether the information that makes up a 35mm film (picture and sound) could be compressed and stored somehow digitally on 8mm film (or any other media, for that matter) depends on entropy (amount of information present) and how much loss is acceptable before the human visual and hearing systems notice degradation.
I suspect that this type of digitizing could be done with satisfactory results using lossy compression. It is difficult to even attempt to calculate the "digital bandwidth" of any type of film because the resultion figures I see for film varies depending on the information source. It's a question of how many bits of information could be stored on the film in the form of a rectangular array of "values" in the form of brighter and darker square pixels. For example, if only two brightness values (white and black) are used, how "fine" can the packing of these squares be on the film to be read reliably with a very low error rate? Factor in some redundancy to allow correction of some read errors. It may be better to use more brightness values (several shades of gray, depending on the approach used in building the reader. Once a bandwidth (so many megabits per second) is determined, then it could be determined what resolution could be achieved for picture and sound using current available technology and compression methods.
John Pytlak is probably familiar with the recording of digital data on film, and what resolutions are used (how many quantization levels are used per unit, and at what density the units are stored on film). If so, John (or anyone else in the know), please chime in!
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Evans A Criswell
Huntsville-Decatur Movie Theatre Info Site
cheers Peter
"EBIR FILM AND OTHER STORAGE MEDIA COMPARISONS
Electron beam recording of imagery on film also has specific advantages over recording on magnetic and optical storage media.
A terabyte of uncompressed data can be recorded on a single roll of 9.5" film 235’ long with the EBIR, compared to recording
on 200 exabyte tapes or 217 (4.6 gigabyte) optical disks. The time to record a terabyte of data with an EBIR is 14 hours
compared to 70 hours using exabyte tapes and 275 hours using 4.6 gigabyte optical disks.
The volume of space required to store 1 terabyte of data on a 9.5" roll of film is only 0.1 cubic feet compared to 0.9 cubic feet
of exabyte tapes and 1.6 cubic feet of 4.6 gigabyte optical disks. This volume does include any mechanical mechanism for
storing and retrieving the media i.e. optical jukeboxes, magnetic tape drives, etc.
The cost of the media for storing a terabyte of data on exabyte tape is 2.8 times higher and optical disk is 35 times higher than
EBIR film.
Another advantage of film, is that the film is archival and its images may be viewed at any time in the future (hundreds of years)
using optical readers. Film is not subject to explosive technology changes causing obsolescence of digital reading equipment for
image data retrieval."
9.5' = does this mean 9.5mm?
cheers Peter
quote:
Evans wrote:I disagree with the comparisons in the first HTML page. The comparisons are OK, but I feel that some of the resolution figures are a bit misleading. All NTSC formats have information on 525 scan lines, of which 480 are used. This means that there are 480 scan lines of information on DVD, Laserdisc, VHS, Super VHS, or any other NTSC format that encodes all scan lines.
That's something that has always confused me, too. NTSC is a 525 (480 active) line format, yet people always refer to VHS as "about 240 lines resolution", and present similar numbers for other formats (300 for laserdisc, 330 for broadcast, 400 for S-VHS, etc.).
A quick search revealed a couple of webpages that attempt to explain this difference, but neither explanation is entirely satisfactory:
http://www.questronix.com.au/html/info_resolution.htm
http://www.elitevideo.com/new2.htm
Reading those links helped, but I still don't quite understand how an analog video signal can have less than the number of lines in the NTSC standard. If I could just find a source that gave a full explanation (not watered-down) that would help immensely. Anyone have any suggestions?
In the example above, the left box has a source material of 100 lines. The right box has a source material of 200 lines, but the box's limit is 100 lines and the image blurs together.
If you have an image of 525 lines of NTSC and store it on VHS tape, the tape's (horizontal) resolution limit is about 240 lines, so the image becomes blurred together. When you go to play that tape on your TV, even though the TV can reproduce 525 lines (480 visible), the source (the tape) is only 240 lines and looks blurry on TV.
Therefore, the better the resolution of your storage media (tape, DVD, etc.) the sharper the picture will appear when it is reproduced.
Incidentally, optics have a resolution, too. You can run a test loop on a film projector and see how close the lines on the screen can get before they blur together. And have you ever had an eye exam with a chart (you know, with the big E on top)? You're checking the "resolution" of your eyes.
Hope this helps. If not, I can try again.
1. The quality of the media. For magnetic media: How close the particles are, and how thick the coating is. The more particles per area, the higher the resolution and therefore the more data that can be stored. As the coating thickness increases, so does the amount of data that can be stored before bleeding (or blurring) occurs. Lower quality media also shows wear faster ... as the magnetic material wears off, the data "signal" becomes weaker (the data resolution decreases and data loss increases).
2. The size of the media. Obviously, you can stuff more video information on a 3/4-inch or 1-inch tape than you can on 1/2-inch VHS.
3. The speed of the media. The faster the media is moving, the higher the bandwidth for a given period of time. Ie, 15ips on 1/4-inch audio tape has more data than 7ips.
4. The format of the data. How are brightness and color data stored? Do they coexist in the same media area or are they discrete? (See Evans' post above about color and luminance)
For DVD, picture data is stored in a pixel format. Each pixel has its own color and brightness value. DVD stores 720 pixels per line for 480 lines, resulting in phenomenal bandwidth requirements, even with compression.
In regard to using film to store digital data, it all depends on the grain resolution of the film stock and the methods of data recording and of data retrieval and processing. I wouldn't go with any type of color or greyscale, as your reader light might be dimmer than mine, causing a color value of FF (white) to read as 66 (medium grey) unless the reader is recalibrated to the light source with every use.
Then there's the issue of bandwidth. I seem to recall that the Wizard of Oz was reworked at a resolution of 4K x 3K. Using only binary data (black/white or off/on), that's only 12 megabits (or about 1.4 megabytes - think 3.5-inch floppy disk) per frame on an academy aperture. And that's with no redundancy or checksum for error correction.
In my opinion, that electron beam thing sounds too expensive for anything other than government use.
Sorry for the long post.
One can visually measure the horizontal resolution of a playback system by looking at the wedges of a SMPTE resolution chart, available on VHS (SMPTE), U-matic (SMPTE), LD (Video Essentials) and DVD (Avia, Video Essentials).
Typical luminance horizontal resolution numbers:
VHS about 240 lines.
Off-the-air NTSC about 330 (approx 80 lines per MHz).
Super VHS and LD about 400.
Chroma resolution will be about half that of the luminance, designed that way for NTSC/PAL or 4:2:2 since the human eye sees fine detail only in B&W (rods having a much smaller cross-section than cones).
Think of a video image as being like a comic book image--the fine detail is done with a pen, the colors are applied with a brush.
Home tape formats will be somewhat worse since they are all color-under systems.
Oops, once again I have talked too much.
Paul
SMPTE Hollywood Section
Mercenary Projectionist
"When the money runs out, so does I!"
Long Beach, CA USA
While I do understand the concept of bandwith limitations, I don't quite see how it works with analog video -- it's not a continuous stream, it's divided into scan lines. And I assume there has to be some kind of pulse that signals when one line ends and the next begins. If so, does that mean VHS actually has fewer of these pulses per field/frame than full NTSC resolution? If so, how does that get converted to the full 525 lines for display? Or does it? Can TVs simply spread their scanlines out further and have fewer of them on screen (making them, in effect, like multi-sync computer monitors)?
Sorry, I'm really displaying my ignorance here. These must seem like stupid questions to someone who really knows about video. The explanations regarding picket fences and ladder rungs are interesting, but they don't really address what I'm having trouble with. I guess I need to just go to the library and see what I can find out. Thanks to everyone who replied, though.
Oh yeah, and I guess this thread which was supposed to originally be about digital formats has now been hijacked into being about analog video...
VHS, Laserdisc, S-VHS, and DVD all have 480 visible scan lines of information, and all output NTSC signals with 525 scan lines for an NTSC signal (with the same number of sync pulses). DVD actually encodes 720 pixels per scan line for the visible portion. The analog formats encode scan lines, but each scan line is a continuous analog signal and is not discrete (meaning it's not made up of pixels). A VHS picture is made of the same number of scan lines as the output of a TV broadcast, a Laserdisc player, an S-VHS player, etc, but the information that can be recorded on each scan line is less than all the others. It's not that VHS has fewer scan lines, it's just that each scan line can hold less information, resulting in a less detailed picture in the horizontal direction. The resolution in the vertical direction is the same as any other standard NTSC format. It's the resolution in the horizontal direction that suffers. VHS pictures are not made up of "pixels", and neither are S-VHS, Laserdisc, or any other analog video source.
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Evans A Criswell
Huntsville-Decatur Movie Theatre Info Site
Okay, I said I was displaying my ignorance, but I'm not that ignorant!
I understand the difference between digital and analog video. I know that of NTSC's 525 lines, only 480 are active, and that DVD is 720x480 discrete pixels.
I also understand that while analog video formats are divided into discrete rows (i.e., scanlines), they are not divided into discrete columns. There are no pixels, each scanline is just one continuous (albeit bandwidth-limited) stream. One can assign a pseudo-value as to how many columns the lines contain (and say that there are "about 300" or however many), but it's just an approximation, and not an actual, discrete number. I get that much. I'm with you that far.
What I didn't understand is that some explanations (such as the web pages I linked to earlier) really did seem to imply that there are fewer rows (i.e., scanlines) in some analog video formats than others. When they talked about "horizontal resolution", I misunderstood and thought that meant there were fewer scanlines. I was wondering how that could possibly be, since the 525/480 number sounds as though it is fixed.
However, after reading Paul Mayer's post again (thanks, Paul!), I realizing I was just misreading and getting confused about "horizontal" and "vertical" resolution. I suspected that might be the case, and it makes a lot more sense to me now. Sorry about all the needless questions.
The trouble with WWW sites is you never know if the creator of the WWW site has sufficient technical knowledge. Someone can make a neat-looking WWW site and draw nice diagrams saying that the resolutions of different formats is such and such, even if the information is wrong. When you see such information, it may be right or it may be wrong. I'd trust information from a reference book more than from a random WWW site. I've seen incorrect information on WWW sites made by reputable companies.
Another problem is that some digital motion picture formats are lower resolution than NTSC. I have seen some TV commercials where it was obvious that the commercial was rendered for a fewer number of scan lines than standard NTSC, and some sort of scaling algorithm was being used. I see this fairly often, and wonder why they do it. Such a format may have approximately the same resolution as VHS (or more resolution that VHS). If VHS is roughly 240 by 480 (480 scan lines), then a digital format with a resolution of, say, 512 by 384 (284 scan lines) has more resolution, in fact, 71 percent more, but due to the processing required to change the 384 scan lines to 480 scan lines to make a standard NTSC signal, and the fact that broadcast TV is going to limit the bandwith of the signal to around 330 "lines of resolution" per scan line, a commercial rendered that way may look inferior to a VHS tape due to the artifacts created by the scaling from 384 scan lines to 480.
The interlaced nature of video makes things more complicated. You can think of video as consisting of 60 frames per second (except call them fields) at half the vertical resolution, since only half the scan lines get displayed on each screen refresh on a standard NTSC set. If material is recorded for TV with a standard TV camera, then there will be motion in every field. That is, the two fields that comprise a frame will be different. You probably don't want to stick those two fields together and encode them as a single picture with 480 scan lines in that case. In this case, each field can be encoded in sequence, each requiring a vertical resolution of only 240. Interlacing in TV cameras and monitors is a quite complex issue, complicated even more by digital video cameras and issues in digital encoding, as well as conversion of an interlaced video signal to a progressive one. I don't completely understand all of the issues involved myself, but I tend to look at each format in terms of how much resolution could be present in ideal cases. For example, an interlaced signal from a VHS tape could have 480 true scan lines of information since the 3:2 pulldown method of recording the movie would allow the fields to be weaved together to produce progressive images, since there would be no motion between fields that were scanned from the same film frame. You could not do the same with a VHS tape of a football game shot with a TV camera, where vertical resolution has been traded for temporal resolution. Interlaced video creates interesting issues concerning vertical resolution and temporal resolution.
However, even if a digital format has fewer scan lines than NTSC and can take advantage of the interlaced nature of an NTSC signal and "cheat" and get by with encoding a lesser amount of vertical information (scan lines) than 480, that looks just as good on a standard TV, I still argue that the signal is inferior to a signal with 480 scan lines encoded per frame, since such a signal, if from a film source, can be line doubled to produce a progressive signal, while the format with fewer scan lines encoded would require interpolation to display 480 lines, which introduces artifacts.
An interesting article is Interlace or Progressive Scanning by John Watkinson, Watkinson International Communications, available in Pixels, Pictures and Perception: The Differences and Similarities Between Computer Imagery, Film and Video from SMPTE.
Personally, I'd like to know more about the digital encoding of interlaced NTSC myself, and how systems that use fewer than 480 scan lines of information work.
I'm looking at the WWW site http://www.elitevideo.com/new2.htm and see one error already. .7 x 483 is not 240. Computer and video resolution is measured in terms of how many pixels (how many changed from white to black) can be stored rather than how many pairs of changes from white to black can be stored. Film folks say that a resolution of 480 is the ability to store 480 pairs of white and black lines, while video and computer folks would call this a resolution of 960, since that's how many pixels would need to be there. The Kell factor comes from aperture effects inherent in tube cameras and CRT devices. The Kell factor varies depending on the apertures of the systems in use and may not always be .7 . This Kell factor does not mean that the resolution of a given video format is less. It simply means that it may be less when displayed on a CRT, or may have been limited if a tube camera was used.
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Evans A Criswell
Huntsville-Decatur Movie Theatre Info Site
It is interesting that consumer electronics have surpassed a national TV network.
Joe, in my opinion, home electronics surpassed broadcast TV (I'm talking standard analog) when Laserdisc came out.
About this interesting Kell factor:
I got my copy of Fundamentals of Television Engineering by Glenn M. Glasford, 1955, and this Kell factor is discussed on pages 26 and 27. There is a discussion of the position of the scan lines in relation to vertical detail, and the Kell factor being determined by either "subjective methods, or a more complex theoretical analysis". It mentions two different subjective techniques from which the Kell factor was determined to be 0.64 in one case (using a test pattern with a tapered wedge of almost horizontal converging lines) and 0.71 in another (based on reproduced with of a single line when crossed by the scanning lines). Using different test patterns leads to different Kell factors.
As I said before, the characteristics of the display device itself and even the camera used to record the images will also affect the Kell factor (and this is a separate ddiscussion from the one in the above paragraph).
But, when we speak of resolution, what the hell are we talking about? Different people mean different things when they speak of resolution, and I'm seeing that when I research this topic. The discussion from the Fundamentals of Television Engineering book, when discussing the Kell factor, is speaking of resolution in terms of how many pairs of alternating bright and dark lines can be displayed. Specifically, when speaking in terms of scan lines and the Kell factor, the question is, "With a certain number of horizontal scan lines, how many pairs of regularly spaced alternating light and dark horizontal lines can be discerned on the display device?" As a computer scientist, my question is "How many 'pixels' of information could I store on the picture in a column from top to bottom?" These are two different measures of resolution and in discussing either TV displays or the resolution of an image file, can produce nonintuitive differences in the answer depending on what is meant by resolution.
I'll tell you my opinion about this "Kell factor". It seems to be a subjective measure of how much interference from beat patterns is acceptable or not acceptable. Let's look at this "reduction of resolution by the Kell factor" in reverse. Let's say I have 32 pairs of alternating solid white (value 255) and solid black (value 0) horizontal lines. Obviously, with 64 scan lines, I can display these perfectly (assuming the display device is capable of displaying all the scan lines without the scan lines overlapping, which is an entirely different issue, that I'll get to later -- called aperture effects). Suppose I have to use 70 scan lines instead of 64 due to the display device requiring that frequency. A beat pattern will be created that will interefere with the information due to the resolution change (signal resampling). Although my display device can now handle 35 pairs of alternating white and black lines, it cannot handle 32 well at all due to the beat pattern caused by the resampling. So now the question is, how many scan lines do I have to use to create a display of the 32 alternating lines. I'm going to let each of you find that out on your own. Go here . Take the test and report your Kell value here. This will be interesting.
To say that a Kell Factor is 0.64 means that you have to use 100 scan lines to display the 32 alternating pairs of white and black lines and be able to discern them. The ability to discern is a bit subjective, and the characteristics of each of your monitors may be different, so I expect your answers to be different.
Now, the other thing that causes loss of resolution on a display device is aperture effects. An electron beam scanning across a picture tube is not a point, but rather a spot that has size and shape, and this size and shape affect the frequency response of the display device. Extraneous patterns are created if the scanning spot is so small that there is black space between the scan lines, but a scanning spot too large causes overlap in the scan lines, which results in a blurring of the image. This blurring would reduce the number of alternating white and black lines discernable.
So, if it is determined that on a given TV display, only 320 equally spaced horizontal lines are discernable, then it could be due to the Kell factor, aperture effects, or both.
However, I still stand by the claim that 480 scan lines of information must be encoded in the source material to get the maximum resolution out of the display device. If, due to Kell effects, 320 scan lines are discernable on a given display, and source material, as a result, is encoded with only 320 scan lines, thenthere first must be a conversion (resampling) from 320 to 480, which introduces a beat pattern in the signal and degrades it from its original form, before Kell and aperture effects take further toll on the signal when being displayed. You can't say that just because of Kell or aperture effects, that the resolution of, say, VHS, Laserdisc, or DVD is less than 480 scan lines.
The unfortunate result of all of this is that there could be 3 differenct resolution figures reported for the same device:
N (number of raw pixels)
N/2 (pairs of white/black lines displayable by alternating pixels)
K * N/2 (pairs of white/black lines displayable taking Kell factor into account)
Also see the thread entitled "Digital projection challenges - resampling and rotation" in the Film Handler's Forum from March 23, 2001.
Thinking of objectionable patterns in everyday television, even at low resolutions, these seem to be surprisingly rare, largely due to educated videographers avoiding potential problems. The Hitchcock Cary Grant film about the cat burglar is one (the name escapes me at the moment). Grant wears a herringbone jacket in the film and there are stripes in the shirts that moire badly. Other than that notable exception, I am rarely bothered by beat freq. artifacting on television.
More specifically, the technology of using scan lines is inferior in resolution to film vertically, but has the potential to be better than film horizontally. This is a known trade-off. The solution to scan line problems lies in finding a suitable pointalist substitute that can send a similar amount of information in the same size data stream, and not require an unworkable yoke circuit. Random dots with a certain amount and percentage of overlap could provide a more flm-like experience, but I can't imagine the circuits involved.
An improvement that would be within current technology would be to scan horizontally on one interlace and then scan vertically on the other interlace. This would increase the problem on one axis but reduce it on the other, and result in a _perception_ of a much clearer picture in both dimensions. The problem with this improvement is finding a way to change millions of tv sets...
quote:
An improvement that would be within current technology would be to scan horizontally on one interlace and then scan vertically on the other interlace. This would increase the problem on one axis but reduce it on the other, and result in a _perception_ of a much clearer picture in both dimensions. The problem with this improvement is finding a way to change millions of tv sets...
Wow. If the interlacing was done this way, it would surely make analyzing the resolution and other aspects of the signal fun. The odd fields and even fields would have totally different frequency responses on the CRT device (assuming the apertures (size and shape of scanning spot) to the the same on both).
I think a projection system where all the pixels in the image could be set to their proper value all at once rather than being set in a top-to-bottom fashion, would be better than either an interlaced or even a progressive system. A memory-mapped system in which each element instantly becomes the proper color (and holds that color) based on the contents of it's mapped memory address would allow screen refreshes as fast as the memory could be refreshed by the underlying software. The frame changes could then appear like film, except without the shutter flicker and loss of light due to the shutter mechanism having to block the light while the film is traveling.
quote:
Evans, you seem to fixate on the beat pattern problem in scan line based systems. While I agree that this is an important aspect of resolution, it is not a be-all and end all-measure of quality.
Well, beat patterns and aliasing are new issues that come up when discussing digital imaging systems that you don't have to worry about when working with film with a random grain distribution. I emphasize it because 1. The topic is very interesting to me personally, and 2. I feel that it's a topic that many people overlook. I admit that I did not understand the Kell factor until today, when I actually read the only book I had that discussed it in detail, and did my own experiment. I learned something that I didn't previously know, even after years of working with digital images, and wanted to spread it to other people here.
The reason you're not bothered by a lot of beat patterns when you watch TV is that most scenes that occur do not have regular patterns with frequencies between 120 and 240 pairs of light/dark lines of resolution that occur over a significant area of the picture. Like you said, some suits and shirts have such patterns. Aperture effects in the cameras help to eliminate some of these effects since the camera's scan lines may have overlap and produce some blurring, just as aperture effects cause blurring on a monitor in some cases.
I didn't say that these issues are then be-all, end-all measures of quality, but they're issues that must be taken into account and dealt with any time that images are resampled to different resolutions during the process of doing CGI work or converting camera resolution to film recorder resoluton, converting to HDTV, or converting to NTSC.
Another interesting topic is subjective appearance. The mathematically better approach may not produce the most pleasing effect to the human eye and brain.
No need to apologize; you were trying to help after all.
If the web were the only place I had seen that explanation, I would not have given it much credibility. But I swear I've seen that same sort of thing in books and magazines for years -- and it always confused me.
Anyway, thanks to everyone for helping to clear this up. It's always bugged me.
quote:
If the web were the only place I had seen that explanation, I would not have given it much credibility. But I swear I've seen that same sort of thing in books and magazines for years -- and it always confused me.Anyway, thanks to everyone for helping to clear this up. It's always bugged me.
I've seen these figures too and they'd always bugged me, and I finally wanted to do some research into the topic and understand it myself. That's why I went into such long-winded posts about it, and is why I made some test patterns.
I am employed at an academic institution on the research side, and I'm also working on a Ph.D. in Computer Science, and have a fairly strong mathematical background (B.S. degree, 1987) and feel that if I don't understand something well enough to explain it mathematically, then I don't understand it. Doing that research two days ago introduced me to something I'd never thought about before. Surprisingly, out of all the graphics and image processing books I have, only one discusses the Kell factor in enough detail to understand it. So, I played with it, and made test patterns, and was surprised by what I saw in the test patterns. I knew that beat patterns would appear if I reduced the resolution by a few pixels, but wasn't expecting the same thing when I increased it.
I totally agree, and if there is one area where the variations in resolution need to be taken into account, it is during copying and resampling. Just as the major syndicated tv shows were smart to film with 35mm and supply reduction prints to 16mm, anyone in production today is probably smart to continue using 35mm or larger random grain based source material. Jumping to digital at that end might be cheaper, but as digital resolutions change and (possibly) increase, later use of those early digital sources will become problematic.
Even though I have pretty much retired my enlarger in favor of scanned negatives and Photoshop, I still shoot 35mm color neg for the detail and (touch wood) relative permanance. Eventually, I may buy a digital camera for everyday use, but I'm not rushing out to pay a lot for something that won't give the flexibility or resolution that I want.
OTOH, what I have found useful and somewhat fascinating in concept is using a camcorder and a Snappy multiple frame grabber to generate stills. I find the idea of sampling multiple frames to get an image that is free of noise and has more resolution a fantastic idea. I am surprised that the technology hasn't been used on some of the early films where only poor prints are available.
The idea is based on the classic best two out of three or three out of five concept. In multiple frames of the same subject, any image data in a perfect sequence will be identical. If one of those images has noise, it will be quite different. By ignoring data that goes beyond a set threshold, then averaging (taking the mean of?) the remaining image information, a single image can be formed that is far superior to the original images.
In old films, that image could be used as the master image for a scene. Moving objects are a little more complicated, but do-able, to the point that some early footage could probably be brought up to close to modern day standards.
The result would be lacking in grain, so a certain amout of grain noise would have to be re-introduced to give an authentic look.
Every technology has its own weaknesses and strengths. Sorry if it sounded like I was busting your chops on resolution pairs. I just wanted to bring the issue into perspective.
quote:
The idea is based on the classic best two out of three or three out of five concept. In multiple frames of the same subject, any image data in a perfect sequence will be identical. If one of those images has noise, it will be quite different. By ignoring data that goes beyond a set threshold, then averaging (taking the mean of?) the remaining image information, a single image can be formed that is far superior to the original images.
We covered this "frame averaging" technique in the image processing class I took earlier in the year! Basically, assume that a noisy image g(x,y) is formed by adding noise n(x,y) to an original (unavailable) image f(x,y). All we have is g(x,y), and
g(x,y) = f(x,y) + n(x,y)
If multiple images are available that were all derived from f(x,y), but with different distributions of noise, then averaging the images will reduce the magnitude of the noise in the average by the square root of the number of images averaged. (Take the standard deviation!) That is, by averaging 4 images, the noise magnitude can reduced by a factor of 2.
This technique is useful if all captured images are of the same thing, and in that case, works even all the images are noisy (with differing random noise). A side effect of this technique is a slight reduction in contrast due to a slight increase in black level and reduction in white level. My professor who taught the image processing course disagreed with me when I brought this point up, but I still say that such a slight degradation in contrast will occur since if the original scene has totally black and totally white areas, and became corrupted with noise, values in the middle of the scale are equally likely to be increased or decreased due to noise ( averaging out to a net change of 0), but low values near 0 are more likely to be increased, since values below 0 are not encoded, and values near 255 are more likely to be decreased, since values above 255 will not be encoded. Therefore, black areas will be more gray in the averaged image, and white areas will be slightly darker in the averaged image, while values in-between will be closer to their true value. In real-life images where the noise is of small magnitude, it will not be a problem, but if the original images have many values near black and/or near white, and noise is great, it could be.
This method was first proposed by Kohler and Woods in 1963 (see paper reference below).
References:
Gonzales, Rafael C. and Woods, Richard E. [1992], Digital Image Processing, Addison-Wesley, pp. 187-188. -- a standard textbook used in many graduate-level image processing classes at universities.
Kohler, R. J. and Howell, H. K., [1963], "Photographic Image Enhancement by Superposition of Multiple Images", [i]Photogr. Sci. Eng., vol. 7, no. 4, pp. 241-245. -- the original paper.
What you seem to be describing is a simple averaging, which is inferior to a threshold limited averaging. Crude example:
On a scale of 0 to 256 for brightness, we measure the single corresponding pixel on 5 noisey images. They are
0
100
95
110
15
We find the "best three" numbers that are closest together -
in this case 100, 95, and 110 (This example doesn't account for surrounding pixel values)
We then find the max variation between the best three, which is 15
We then arbitrarily double that to set the threshold to 30.
Anything outside of the aprox average of the best 3 (102) by 15 points or more is discarded as being too corrupted by noise to contain useful data.
In this case, the image comes out at that 102 value.
In a straight averaging of all images, The noise would cause that value to drop well below the lowest reasonable value, 95, resulting in image degradation.
As early as the sixties, NASA reported on a precise technique to refocus poorly focused images based on weighted averaging. Some of the current imaging programs use a popularized version of that technique in their "sharpen" filters.
The example I gave above uses only 5 data points. If a full second of film were used, the results would be much, much better. If weighting were given to surrounding areas, the image might be improved further.
"Digital Intermediate" where film is scanned, digitally manipulated, then output back to film, offers immense flexibility in manipulating and enhancing the image, including sharpening and grain reduction:
Digital Intermediate
Kodak's Glenn Kennel Talks About Digital Intermediate
O Brother Where Art Thou?
Kodak and the Future
------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
quote:
As early as the sixties, NASA reported on a precise technique to refocus poorly focused images based on weighted averaging. Some of the current imaging programs use a popularized version of that technique in their "sharpen" filters.
Is this a convolution technique that you're referring to, or another, more complex technique?
Most sharpening filters in today's software are implemented as convolution masks, which is a weighted average of points within a square neighborhood of each given point in the image. Believe it or not, if you're willing to make the convolution mask large enough, it is possible to implement nearly any frequency-domain filter in spatial domain by finding a convolution mask using a least-squares approach which approximates the frequency function. The main reason that NASA is interested in doing such processing in spatial domain rather than in frequency domain is that convolution can be done as new scan lines of the image data become available for processing, and it's straightforward to implement, although for large images and convolution masks, can get very computationally expensive. Try convolving a 1024 by 1024 image with a 1024 by 1024 convolution mask without using FFTs and IFFTS to convert to a frequency-domain point-by-point multiplication of the transforms. Normally, small convolution masks, such as 3x3, 5x5, 7x7, are used, which don't create such a computational burden, and small masks can give surprisingly good blurring or sharpening results.
About the thresholding you mentioned on the image averaging topic: The more knowledge you have about the actual noise, the better off you are in being able to improve the algorithm. If you know that the noise is not random all of the time, and "dropouts" or "spikes" occur in small parts of the image, then throwing out any point outside a certain range of the median of a point's neighborhood, or the median of the point's value from all of the images, will result in a better average. However, this improvement assumes more knowledge about the nature of the noise than assuming it is random. If the noise is truly random and you have absolutely no other information about it, then you're just as well off doing a straight average. If you can determine a good approximation of the standard deviation of the noise, then you have a good basis for determining a reasonable threshold to use in rejecting bad points.
Common sharpening filters are edge enhancement oriented, which is a weak form of enhancement.
From Photoshop help:
"The Unsharp Mask filter locates every two adjacent pixels with a difference in brightness values that you specify, and then increases the pixels’ contrast by an amount that you specify. In addition, you specify the number of surrounding pixels to which the sharpening effect is applied."
Now to describe the NASA system, as I remember it. I couldn't find the old paper abstract, and I am not a math whiz, so I'll try to describe the concept in lay terms.
The first part was a recognition that each lens is different and it was ideal if the original lens could be on hand to examine it's individual characteristics. However, the general concept could be applied to any lens that had an out-of-focus image.
The concept relied on the out-of-focus image being more or less on a single depth plane. It took the known circle of confusion for a specular and used that as a template for a circle, where if there was evidence of a similar circle on the image, that circle would be negated and a corresponding point source inserted at the center. That point became a wild card in further image extrapolations.
You can visualize one of the patterns involved by viewing the airy disk found in a defocused telescope. A star is for all intents a near perfect point source of light, so the rings found when it is defocused in a telescope gives an indicator of exactly how that lens system will deform any defocused image.
Star Test
Next, you can see a diagram of how an image that is defocused will subtend a larger area on the negative.
Auto focus example The important points to remember are that the defocused point image will be circular and there will be a pattern to the brightness in the circle, generally with the center being brightest, with a tapering off to the edge, where the diffraction pattern will form "ripples."
The weighting to negate the defocused bright spot is actually close to an inverse of the diffraction chart shown on this site Lens Tutorial
As I remember, the idea was to pick the peak speculars first, correct them, then notch down a level and correct the next brightest speculars and so on, each time checking for the presense of the characteristic pattern. The process continued to the limits of the resolution and gamma curve of the film.
I see all the math on the sites, but I'll confess it is beyond me and I have little interest in massaging the figures to verify the concept. I have no doubt that it would work on a star field, and I suspect it would work quite well on high contrast subjects photographed out of focus on high resolution film. It would work poorly on low res. digital images.
Finally, as I remember, there was the idea of having different patterns for motion smearing, that would do much the same thing. I'm guessing that image enhancement techniques like this were used on the first Hubble images.
So much for that.
I disagree with you about averaging all points in truly random noise. Intuitively, it doesn't make sense. First, true randomness is surprisingly rare, and "random" noise may not be entirely random, but could follow a curve, making it possible as you suggest to toss out values outside of the median. In any case, the image itself is not random, and greater weight of importance needs to be given to values falling within the expected values of the image. I believe this is where the reduced contrast you were talking about creeps in to your enhanced images.
I'm not sure how the 'digital intermediate' as described falls within the center scope of this, although it is an interesting sidebar.
On the light side... When I see the "digital enhancement" of images of UFOs, I have two reactions. The first is to laugh out loud, since the enhancement is usually a cheesy and blocky false color image, and the second is to wonder just how many of these could be properly resolved by the use of a combination of the technique I just described and multi-image averaging. I suspect that a lot of planes and balloons and fakes could be found.
Whatever. I don't think I'm giving away any state secrets, since what I have related was in an early open NASA publication, and the technical expertise to pull this all off would have to be substantial.
Since the net address was probably already on my local drive when I was first having problems, I'm a little puzzled how such a problem could occur.
When I access at home on a dialup through a different ISP, it's all good.
Brad, next time I have a delay problem, I'll email you the time and my IP address so you can check the request logs.
Now back to our regularly scheduled topic ...
I'm not discounting the possibility of the DNS routing, but I've yet to experience it.
No problems today, but here's today's stats for future reference:
code:
Pinging www.film-tech.com [207.168.10.69] with 32 bytes of data:Reply from 207.168.10.69: bytes=32 time=94ms TTL=241
Reply from 207.168.10.69: bytes=32 time=95ms TTL=241
Reply from 207.168.10.69: bytes=32 time=95ms TTL=241
Request timed out.
code:
Tracing route to www.film-tech.com [207.168.10.69]
over a maximum of 30 hops:1 3 ms 2 ms 3 ms 10.1.1.254
2 1 ms 1 ms 1 ms 10.100.1.252
3 3 ms 2 ms 2 ms 206.141.185.1
4 7 ms 7 ms 7 ms 199.179.99.1
5 10 ms 9 ms 9 ms 199.179.0.242
6 17 ms 17 ms 17 ms atm3-0x6.nap1.mich.net [198.108.22.230]
7 * * 17 ms acr2-serial6-1-0-0.chicagochd.cw.net [208.172.1.169]
8 18 ms 18 ms 18 ms corerouter2.willowsprings.cw.net [204.70.9.146]
9 20 ms 18 ms * core3.willowsprings.cw.net [204.70.4.25]
10 19 ms 19 ms 21 ms atm1-0.chi-c100.gw.epoch.net [206.220.243.61]
11 73 ms * 72 ms pos0-1.sfo-c000.gw.epoch.net [155.229.123.141]
12 74 ms 73 ms 74 ms pos8-0.pao-c001.gw.epoch.net [155.229.57.197]
13 81 ms 80 ms 81 ms pos3-0-0.lax-c100.gw.epoch.net [155.229.120.50]
14 90 ms 112 ms 90 ms pos0-0-0.dal-m100.gw.epoch.net [155.229.123.126]
15 95 ms 95 ms 95 ms 209-101-238-138.dal-m100.cust.gw.epoch.net [209.101.238.138]
16 * 96 ms * www.film-tech.com [207.168.10.69]
17 97 ms 96 ms 98 ms www.film-tech.com [207.168.10.69]Trace complete.
That's kinda neat to see ... Detroit -> Chicago -> San Francisco -> Los Angeles -> Dallas
Everyone knows that the Mac is not powerful enough to edit video.I hate cache. Sometimes it is necessary, but most of the time I wish that it didn't exist. Without it is the only way to guarantee that everyone is getting the latest updates on each page. And proxy cache is even worse! Oh, and I just loooove the proxies that don't update themselves but once a day!
Actually the majority of the Quicktimes on this site have been created and edited on my G4 with Final Cut Pro.
code:
Pinging www.film-tech.com [207.168.10.69] with 32 bytes of data:Reply from 207.168.10.69: bytes=32 time=118ms TTL=240
Reply from 207.168.10.69: bytes=32 time=116ms TTL=240
Reply from 207.168.10.69: bytes=32 time=117ms TTL=240
Reply from 207.168.10.69: bytes=32 time=117ms TTL=240
code:
Tracing route to www.film-tech.com [207.168.10.69]
over a maximum of 30 hops:1 2 ms 3 ms 3 ms 10.1.1.254
2 <10 ms <10 ms <10 ms 10.100.1.252
3 2 ms 2 ms 2 ms 206.141.185.1
4 8 ms 7 ms 7 ms 199.179.99.1
5 10 ms 9 ms 9 ms 199.179.0.242
6 17 ms 17 ms 17 ms atm3-0x6.nap1.mich.net [198.108.22.230]
7 18 ms 17 ms 18 ms acr2-serial6-1-0-0.chicagochd.cw.net [208.172.1.169]
8 19 ms 18 ms 18 ms corerouter2.willowsprings.cw.net [204.70.9.146]
9 107 ms 105 ms 103 ms core3.willowsprings.cw.net [204.70.4.25]
10 22 ms 19 ms 19 ms atm1-0.chi-c100.gw.epoch.net [206.220.243.61]
11 72 ms 72 ms 72 ms pos0-1.sfo-c000.gw.epoch.net [155.229.123.141]
12 73 ms 73 ms 75 ms pos8-0.pao-c001.gw.epoch.net [155.229.57.197]
13 82 ms 83 ms 81 ms pos3-0-0.lax-c100.gw.epoch.net [155.229.120.50]
14 113 ms 112 ms 112 ms pos0-0-0.dal-m100.gw.epoch.net [155.229.123.126]
15 117 ms 116 ms 116 ms 209-101-238-138.dal-m100.cust.gw.epoch.net [209.101.238.138]
16 119 ms 117 ms 118 ms www.film-tech.com [207.168.10.69]Trace complete.
quote:
Now to describe the NASA system, as I remember it. I couldn't find the old paper abstract, and I am not a math whiz, so I'll try to describe the concept in lay terms.The first part was a recognition that each lens is different and it was ideal if the original lens could be on hand to examine it's individual characteristics. However, the general concept could be applied to any lens that had an out-of-focus image.
Thanks, Jerry, for providing the details on that NASA sharpening algorithm in your earlier post. I have 2 books consisting of nothing but important papers in the fields of image enhancement and restoration, and several of the articles deal with the topic of deblurring. One specifically deals with deblurring using the principles of optics. This is such a neat area because much of the research, besides just being for theoretical interest, is very practical and applicable in the real world.
By the way, my research work at the University of ALabama in Huntsville is funded by NASA contracts. In fact, I believe every bit of work I've done for the past 13 years has been through contracts with NASA. That's one reason I was so interested in knowing which approach NASA was using for that deblurring. Marshall Space Flight Center, here at Huntsville, has an excellent library with one of the best collection of technical journals in the southeast.
The coolest thing I got to see (a couple of months ago) was a lens fabrication facility out at MSFC. Both mirrors and lenses were manufactured there. I saw some of the largest lenses I'd ever seen. 17-inch diameter lenses were sitting around, and one large machine had a lens that was 30 or 32 inches in diameter (and 4 to 6 inches thick), and it was so clear that the lens itself was hard to see in the machine. On another day, we had visited a very large facility where satellite sensors and embedded processors were made, and the building had a huge high-bay area. Being a movie buff, when looking around, the thought came to mind about how some of those huge lenses and the huge wall of that high-bay area could be used for some giant film format.
Sorry for the delay in response, Jerry, but for some reason, I did not see the replies from June 23rd and on in this thread until this mroning, which I cannot explain, since I keep up with this site at least a couple of times a day.
------------------
Evans A Criswell
Huntsville-Decatur Movie Theatre Info Site
------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
I found that particular abstract intriguing and it happened to stick in my memory. As I recall, it was an idea at the time, and I can see how there would be technical issues of sample size, induced randomness or clumping based on grain structure, orientation effects, etc.
From your past posts I had inferred that you were connected with NASA research.
Target Name: www.filmtech.com
IP: 207.217.96.35
3 5 ms T1-s0-Capital-s2-DTMOB.zebra.net [209.12.14.245]
4 9 ms 905.Hssi4-0-0.GW1.NOL1.ALTER.NET [157.130.68.65]
5 17 ms 132.ATM3-0.XR1.HOU4.ALTER.NET [152.63.96.106]
6 17 ms 193.at-2-0-0.TR1.HOU7.ALTER.NET [152.63.99.146]
7 57 ms 132.at-6-1-0.TR1.LAX9.ALTER.NET [152.63.4.162]
8 68 ms 297.ATM6-0.XR1.LAX4.ALTER.NET [152.63.112.173]
9 60 ms 193.ATM6-0.GW4.LAX4.ALTER.NET [152.63.113.89]
10 60 ms earthlink-gw.customer.alter.net [157.130.231.222]
11 59 ms f5-0-0-cr02-pas.neteng.itd.earthlink.net [207.217.1.44]
12 59 ms v296-dnr01-pas.neteng.itd.earthlink.net [207.217.2.126]
13 61 ms www.filmtech.com [207.217.96.35]
quote:
Adam - trying pinging www.film-tech.com the next time you have a problem and let me know what the delay is. Is there any way of testing this from some point outside the MS proxy box?
This is a cute little freeware program called Ping Plotter (available at ZDNet)
http://www.zdnet.com/downloads/stories/info/0,,34738,.html
It can be set up to ping repeatedly at intervals you set up, average them, & then show the results graphically to see where the bottleneck may be.
It can copy the data as text to the W9x clipboard, or copy it as a graphical representation.
Whoah, looka here!
Target Name: www.filmtech.com
IP: 207.217.96.29
3 5 ms T1-s0-Capital-s2-DTMOB.zebra.net [209.12.14.245]
4 8 ms 905.Hssi4-0-0.GW1.NOL1.ALTER.NET [157.130.68.65]
5 15 ms 132.ATM3-0.XR1.HOU4.ALTER.NET [152.63.96.106]
6 15 ms 193.at-2-0-0.TR1.HOU7.ALTER.NET [152.63.99.146]
7 57 ms 132.at-6-1-0.TR1.LAX9.ALTER.NET [152.63.4.162]
8 66 ms 297.ATM6-0.XR1.LAX4.ALTER.NET [152.63.112.173]
9 62 ms 193.ATM6-0.GW4.LAX4.ALTER.NET [152.63.113.89]
10 60 ms earthlink-gw.customer.alter.net [157.130.231.222]
11 263 ms f8-0-0-cr01-pas.neteng.itd.earthlink.net [207.217.1.75]
12 59 ms v200-dnr01-pas.neteng.itd.earthlink.net [207.217.2.30]
13 58 ms www.filmtech.com [207.217.96.29]
The pages are loading fine now. What, do they only behave while you're in the room watching them?
Seriously though, the server is running just fine and dandy. We're looking into other possibilities for the occasional delays now. It's kinda hard to fix something when you can't replicate the problem yourself, though.
"As early as the sixties, NASA reported on a precise technique to refocus poorly focused images based on weighted averaging"
It is labeled "Supplemental Information Package for HQN-10542" Correction filters remove defects in optical images. Perhaps that will help you find it.
1 success 79ms length=40
2 success 76ms length=40
3 success 78ms length=40
4 success 79ms length=40
Reply from 207.168.10.69: bytes=32 time=249ms TTL=244
Reply from 207.168.10.69: bytes=32 time=318ms TTL=244
Reply from 207.168.10.69: bytes=32 time=247ms TTL=244
Reply from 207.168.10.69: bytes=32 time=250ms TTL=244