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side by side comparison... large print digital back VS 4x5 color film
Most of people using MD digital back claim that it's superior than 4x5 scan for their pro uses (ofset...).
But is there anybody out there that made a comparison between large prints (inkjet or lambda...) that came from MFDB file and 4X5 scan ? same subject (landscapes, architecture, difficult light..) ?
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
archivue
Most of people using MD digital back claim that it's superior than 4x5 scan for their pro uses (ofset...).
But is there anybody out there that made a comparison between large prints (inkjet or lambda...) that came from MFDB file and 4X5 scan ? same subject (landscapes, architecture, difficult light..) ?
There are a couple. I seem to remember one from Charles Cramer. Might be on the Luminous Landscape website. IIRC it's a fairly flawed comparison because the scanner used on the film was a Tango, so the scans were somewhat soft. This is due to the Tango's 11 micron fixed aperture which limits the Tango to something around 2200-2400 ppi maximum optical resolution (that is, what it can read from something like the 1951 USAF Resolution Test Chart).
Even at that when I was looking at the images themselves I picked the film images as somewhat better. That was not the conclusion of the article however. If they had found otherwise I doubt they would have published their findings.
If you find any comparisons that use a better drum scanner (something with a 6 micron aperture more or less, or even a 3 micron aperture) I'd like to see it so post a link.
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Bruce Watson
Might be on the Luminous Landscape website. IIRC it's a fairly flawed comparison because the scanner used on the film was a Tango, so the scans were somewhat soft.
The scans were fine, just that the 4x5 shot was clearly out of focus in the area selected for the comparison (or the film had popped). It makes you wonder when people base purchasing decisions on really amateur tests like this.
There's plenty more to consider than which has the highest resolution. For instance, if you do your sums the working depth-of-focus (namely at the sensor plane) is about a 10th of that for 4x5.
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Re: side by side comparison... large print digital back VS 4x5 color film
What is the price of a P45 system again? Like that used in the comparisons?
Tyler
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Re: side by side comparison... large print digital back VS 4x5 color film
prices ? difficult to say...
in the same shop, you have :
P45+ back only for 26000 euros excluding taxes
while the P45+ phase one kit (including body and 80) is at 19000 euros excluding taxes
A simple P45 refurb cost 11000 euros excluding taxes
and 12000 with a phase one camera and 80... 1 year warranty.
While the canon 5DII will be around 2300 euros including VAT... but that's an other story !
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Re: side by side comparison... large print digital back VS 4x5 color film
P45 refurb kit costs the price of 650 Portra 4x5 (film+C41) and 130 hires scans
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Tyler Boley
What is the price of a P45 system again? Like that used in the comparisons?
Tyler
I believe it was $39,000. Basically, $1K per megapixel.
Lenny
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
archivue
Most of people using MD digital back claim that it's superior than 4x5 scan for their pro uses (ofset...).
It's 39 megapixels. I get 320 off of a 4x5 piece of film, and 568 megapixels off of 8x10. There's no comparison. The tests are flawed.
That said, one has to get over 360 dpi to get the top quality in color. Almost any digital camera can do that for an 8x10. All you need is a chip where one side is at least 3600 pixels. Digital cameras are great for many commercial uses... And when one goes to the very limited cmyk offset color space, you can't see much difference.
Of course, fine art is another matter....
Lenny
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Re: side by side comparison... large print digital back VS 4x5 color film
That's about the size of it.
I just put up a print in a cafe, a 40x50 inch from a 4x5 slide (Velvia 100). My friend, the one who did the printing (did a good job, btw) also scanned and printed one of his own black and white sheets of 4x5 film, and printed it at 40x50 inches.
The detail in both is incredible; in mine you can walk right up to the print and see the texture in the water, fine detailing in the leafless trees across the bay, and the fine detail in the clouds where the sun's disk isn't overwhelming them. In his, you can see rivets on the bridge, and fine enough detail to separate pairs of cables that look like single cables when you stand back a bit.
Michael Reichmann's now claiming once again that he was right about his assertion that digital outperforms film... but I have yet to see a digital image from anything short of a BetterLight scanning back come even close.
Oh, and my friend doesn't have a drum scanner or anything like that; he has the new Microtek.
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Re: side by side comparison... large print digital back VS 4x5 color film
Don't forget that Reichmann is getting older and his eyesight might not be as good as in the past. Many of the comparisons I read on the internet involve a viewed comparison, which always throws into question the eyesight of the writer.
Ciao!
Gordon Moat Photography
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Gordon Moat
Don't forget that Reichmann is getting older and his eyesight might not be as good as in the past. Many of the
comparisons I read on the internet involve a viewed comparison, which always throws into question the eyesight of the writer.
Ciao!
Gordon Moat Photography
Not just that....his impression changes with the weather as well. Before, he was claiming that his old Canon 1Ds surpassed 6x7 MF film. Now in the most recent test, he found that the new 1Ds 2 was "almost as good" as 645. It sure left me scratching my head.
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Lenny Eiger
I believe it was $39,000. Basically, $1K per megapixel.
Lenny
I just wanted the numbers to be part of the discussion. There's a borderline absurd nature to these discussions that taints the concept of "progress".
Tyler (I use both as appropriate, so don't think I'm evangilising)
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Re: side by side comparison... large print digital back VS 4x5 color film
We talk about this stuff all the time, but honestly why aren't there any published, methodologically sound comparisons out there?
First of all, pick an outcome measure for the comparison. If it's resolution, then why are we looking at crops of trees and not looking at quantifiable resolution targets? Why are we not controlling for critical variables like aperture / diffraction, lens characteristics, and focus? It would make these conversations so much easier if we had something useful to reference.
This just feels like a big rhetorical pissing match a lot of the time, where we find a way to justify (or perhaps rationalize) the superiority of our chosen method, and the best we can do is cite internet heresay or personal anecdotes. Fundamentally the decision of a digital or film system usually comes down to things other than pure decisions about resolution.
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Re: side by side comparison... large print digital back VS 4x5 color film
A good friend of mine, Ron Flickinger, did a lot of testing with his P45 and his Chamonix 4x5. He owns and operates a Screen Cezanne and knows how to scan quite well. He shot the exact same scenes with both cameras, and did prints of each. He sent me 100% samples of each, I think he did an up-res of the digital, and a down res of the film in 2 seperate tests, and the digital won in both on screen, and in prints. The P45 captures 39mp images, but that is compressed, uncompressed i think its around 120mp(don't quote me on that). If you would like more info about the tests, I would suggest to contact him. He is obsessed with quality, and it was enough for him to switch......
Adam Kavalunas
www.plateauvisions.com
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Re: side by side comparison... large print digital back VS 4x5 color film
Thanks, Adam. I myself am not so interested that I'd contact him, but I'd love it if it were either formally published or at least posted on the internet with an open methodology as a resource to us all.
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Adam Kavalunas
A good friend of mine, Ron Flickinger, did a lot of testing with his P45 and his Chamonix 4x5. He owns and operates a Screen Cezanne and knows how to scan quite well. He shot the exact same scenes with both cameras, and did prints of each. He sent me 100% samples of each, I think he did an up-res of the digital, and a down res of the film in 2 seperate tests, and the digital won in both on screen, and in prints. The P45 captures 39mp images, but that is compressed, uncompressed i think its around 120mp(don't quote me on that). If you would like more info about the tests, I would suggest to contact him. He is obsessed with quality, and it was enough for him to switch......
Adam Kavalunas
www.plateauvisions.com
Yes, and the Cezanne is a mediocre scanner. It's blurry in comparison to a top-level drum scanner. Why doesn't he compare something that is reasonable....
Lenny
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Re: side by side comparison... large print digital back VS 4x5 color film
Lenny,
I'm no scanner expert, but I'll give my experiences. I've had drum scans done by many, including 2 Howtek's which many say is one of the sharpest drum scanners. The cezanne scans are sharper. Also, a few years back I think it was Seybold that did a scanner comparison test and the Cezanne came out on top. So to say that it is an unreasonable scanner to use in a test, may be unreasonable in itself. And besides, I just gave my experience in my first post, I said nothing of it being the end all comparison test. Your response was quite arrogant.
Adam
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Re: side by side comparison... large print digital back VS 4x5 color film
Ted Harris thought the Cezanne was a pretty good scanner. Not the best, certainly, but not mediocre. He seemed to know what he was doing.
Lenny, you could've said: "I wonder what the test would've showed if the scan had been done on a high quality drum scanner?" That would've gotten your point across without the negativity or needless controversy.
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Peter J. De Smidt
Ted Harris thought the Cezanne was a pretty good scanner. Not the best, certainly, but not mediocre. He seemed to know what he was doing.
Lenny, you could've said: "I wonder what the test would've showed if the scan had been done on a high quality drum scanner?" That would've gotten your point across without the negativity or needless controversy.
You would think of all people who could settle this Lenny has the equipment and the motivation. What about it?
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Re: side by side comparison... large print digital back VS 4x5 color film
But not the needed objectivity.
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Re: side by side comparison... large print digital back VS 4x5 color film
Just as a point of interest, what is the true optical resolution of the Cezanne Elite when scanning 4X5" film?
Sandy King
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Re: side by side comparison... large print digital back VS 4x5 color film
Hi Sandy,
I own the regular Cezanne, not the elite, and unfortunately I don't have access to the appropriate resolution test slide. Which one do you recommend?
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Re: side by side comparison... large print digital back VS 4x5 color film
Pete,
No idea. I tried to find the answer to my question by looking at Cezanne Elite specifications on the web and came up dry. All I know is that while the maximum optical resolution of the Cezanne Elite is 5300 dpi it can only scan at this resolution in a relatively small strip, about 1 1/2" or 2" wide I believe. To scan anything wider the Cezanne has to reposition the lens and place it farther from the CCD, which results in less optical resolution. I am guessing that the maximum true otical resolution for 4X5" is 2400 dpi -3200 dpi but don't know for sure.
Sandy
Quote:
Originally Posted by
Peter J. De Smidt
Hi Sandy,
I own the regular Cezanne, not the elite, and unfortunately I don't have access to the appropriate resolution test slide. Which one do you recommend?
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Re: side by side comparison... large print digital back VS 4x5 color film
Hi Sandy,
You're right: 5300 spi is only for originals 1.5" wide. When I scan 4x5 one pass, I scan at 2400 spi. For two pass, which involves combining the two scans in Photoshop, I scan at 4000 spi, as I've not found any benefit from doing 3-pass scans at 5300 spi, with my materials and for my uses.
I scan medium format at 4000 spi one pass, and 35mm at 5300 spi one pass.
-Peter
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Peter J. De Smidt
But not the needed objectivity.
How 'bout a "cage match" with Lenny Eiger and Michael Reichmann is a knock down drag out fight to the finish. We can judge if there is no knockout. ;)
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Re: side by side comparison... large print digital back VS 4x5 color film
Edmund Scientifics's variable frequency resolution target 5-200 lp/mm, stock # NT43-488, looks like it would be a good test subject, although since it's rigid, it'd be useless on a drum scanner. Oh, yeah, and it costs almost $500!
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Re: side by side comparison... large print digital back VS 4x5 color film
I'm certainly no expert in the matter, and don't have a dog in this fight, but I understand that the Aztec Premier drum scanner, used by Mr. Eiger and the company I use for my scans, Pixelnation, is one of, if not the best scanner on the market. One of its principal differences is that it captures scan sizes based on the size of the grain of the film, which results in sharper scans.
I too would like to see a side by side comparison of the state of the art original digital source vs. the state of the art analog source. Perhaps Mr. Eiger will assist us, as this discussion is often entertaining, but does not often shed light.
Rick Russell
richardrussell-1@ca.rr.com
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
PenGun
How 'bout a "cage match" with Lenny Eiger and Michael Reichmann is a knock down drag out fight to the finish. We can judge if there is no knockout. ;)
Dude! You almost made me shoot coffee through my nose!
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Rick Russell
I'm certainly no expert in the matter, and don't have a dog in this fight, but I understand that the Aztec Premier drum scanner, used by Mr. Eiger and the company I use for my scans, Pixelnation, is one of, if not the best scanner on the market. One of its principal differences is that it captures scan sizes based on the size of the grain of the film, which results in sharper scans.
I've always found this claim quite dubious. The size of the film grain clumps (dye clouds in color films) vary widely in most films used to capture real subjects with realistic subject brightness ranges. IOW, there is not one single size of the grain of the film -- film grain clump size is fairly stochastic (clump sizes increase generally with increasing density). And the scanner doesn't vary its aperture size as it scans - the aperture size is fixed. So the claim that the scanner "captures scan sizes based on the size of the grain of the film" (and yes, I realize it's not you making this claim, it's Aztek's marketing hype) is a non sequitur.
More on what film grain is and what it actually looks like can be found in Tim Vitale's excellent paper on the subject.
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Re: side by side comparison... large print digital back VS 4x5 color film
I sent Michael an email.
I yam a fight promoter today. ;)
Come on Lenny ... you'll crush the poor fool. Think what it would mean for your business.
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
PenGun
I sent Michael an email.
Come on Lenny ... you'll crush the poor fool. Think what it would mean for your business.
Nothing like a little violence to soothe the soul...
;-)
Lenny
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Bruce Watson
I've always found this claim quite dubious. The size of the film grain clumps (dye clouds in color films) vary widely in most films used to capture real subjects with realistic subject brightness ranges. IOW, there is not one single size of the grain of the film -- film grain clump size is fairly stochastic (clump sizes increase generally with increasing density). And the scanner doesn't vary its aperture size as it scans - the aperture size is fixed. So the claim that the scanner "captures scan sizes based on the size of the grain of the film" (and yes, I realize it's not you making this claim, it's Aztek's marketing hype) is a non sequitur.
More on what film grain is and what it actually looks like can be found in
Tim Vitale's excellent paper on the subject.
Bruce,
There are a number of things that work - that don't make apparent sense... I know you have seen the effects of aperture on scans. It may be based on something else entirely, but you know that sample size (aperture) is a huge factor in the quality of the resulting scan. Too small and you get salt and pepper, too large and you get blurry scans.
The Premier has aperture settings every two or three microns, where the 4500 jumps form 6 to 13, to 19, etc. It's just a little less, altho' 13 works for a lot of things in b&w neg or transparency, so it doesn't matter. The 19 works great for color negs. I don't really need the 8 and the 10 - they aren't used that often.
It's better than the Tango, which is set at 11, and can't vary. Some others have small, medium and large settings, which are not particularly specific.
It's a huge difference when you get it right, however. You end up smoothing the grain just a bit but retaining the sharpness. I think the problem is that there are multiple things going on. First of all, you aren't really looking at grain, you're looking at scan samples...
is it clouds we are looking at? I don't really know. I've invited Tim to come over many times, and he almost has... However, the long and the short of it is that the aperture does do a lot...
Lenny
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Re: side by side comparison... large print digital back VS 4x5 color film
I don't have a problem with using aperture size as a tool to make a good scan. We agree it's a valuable tool.
What I have a problem with is the idea that one can match the aperture size to the grain clump size. The aperture is fixed for the duration of the scan, while the grain clump size varies (sometimes markedly) over the density range of the film. IOW, there is not a one-t0-one correspondence; the laws of physics prevent it.
What setting the aperture size is then is an art. You and I and any other drum scanner operator has to work with the film and decide which aperture is the best compromise of sharpness and smoothness for that particular film. With my own work the correct aperture setting varies from sheet to sheet of the same film developed the same way. IOW it's not a constant under the best of conditions. It's a compromise, and it's that idea of compromise that they completely leave out of the marketing brochures.
It's just the way their marketing says it. In trying to simplify it into a sound bite they get the physics wrong. I hate it when that happens.
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Bruce Watson
It's just the way their marketing says it. In trying to simplify it into a sound bite they get the physics wrong. I hate it when that happens.
I totally agree.
I had many conversations with Phil Lippincott where I would ask a question and get a 2 hour response that had little if anything to do with my question. I think his brain used a language from another planet. However, as I said in a previous post, there are a number of things that don't make sense, yet work a certain way.
I would also agree that setting aperture's and settings is an art, rather than a science, and perhaps that's why the operator is so important. I would add that color management is also an art, way worse than scanning.
Lenny
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Lenny Eiger
I totally agree.
I had many conversations with Phil Lippincott where I would ask a question and get a 2 hour response that had little if anything to do with my question. I think his brain used a language from another planet.
Ah yes. I had some of those oddly frustrating conversations with Phil too. He was certainly a piece of work. Interestingly convoluted thinking. But it seemed to work for him.
Quote:
Originally Posted by
Lenny Eiger
However, as I said in a previous post, there are a number of things that don't make sense, yet work a certain way.
This one makes sense to me. I just can't figure out how to reduce a description of what's going on into a sound bite. Good thing I don't have to!
Quote:
Originally Posted by
Lenny Eiger
I would also agree that setting aperture's and settings is an art, rather than a science, and perhaps that's why the operator is so important. I would add that color management is also an art, way worse than scanning.
Well, at least color management is not a black art. ;-)
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Bruce Watson
Well, at least color management is not a black art. ;-)
Uh, actually, that's what I meant.... ;-)
I bought ColorThink to analyze my profiles and I got all the curves to match up perfectly - then made a horrible print. I called the guy who made it and he said - well, it's just a guide.
A $400 guide... I now make a profile, then print, then make another until the print looks right... and I have iO Table, I know my StudioPrint upwards and downwards and it still doesn't mean its right unless the print works....
Black art? Yes, matey....
Lenny
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Bruce Watson
I've always found this claim quite dubious. The size of the film grain clumps (dye clouds in color films) vary widely in most films used to capture real subjects with realistic subject brightness ranges. IOW, there is not one single size of the grain of the film -- film grain clump size is fairly stochastic (clump sizes increase generally with increasing density). And the scanner doesn't vary its aperture size as it scans - the aperture size is fixed. So the claim that the scanner "captures scan sizes based on the size of the grain of the film" (and yes, I realize it's not you making this claim, it's Aztek's marketing hype) is a non sequitur.
More on what film grain is and what it actually looks like can be found in
Tim Vitale's excellent paper on the subject.
While I would agree film grain clump size can be viewed as a Stochastic function, the
Quote:
clump sizes increase generally with increasing density
is not the reason why. Can you elaborate on this? I checked "Probability, Random Variables, and Stochastic Processes" by Papoulis.
Back to the main point, scanning and film grain, (or whatever one wants to call it), the aperture is being set not to match simply the grain size of film, but the average size of the smallest grain. In Stochastic terms this would be the expected value of grain size. So I agree with what Aztek says, as long as one realizes it's the average grain size that set's aperture. Therefore one should not vary aperture while scanning, If one is set to 10 microns and along comes a dark area that is "clumped" at 55 micron, the 10 micron aperture will read the density properly.
Attached is an intentionally "bad" scan I did with the Premier on Ecke 25, 4K dpi and 8 micron ap. The light and dark areas show the same general "grain size", at least to my eyes.
FWIW I have worked with the folks at Aztek and found them to be straight talkers. This from an EE of 30 years experience that includes designs using PMT's.
Regards,
(West Coast) Tim
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Re: side by side comparison... large print digital back VS 4x5 color film
I have seen what seemed to me very significant grain reduction with software like Noise Ninja, without any apparent decrease in apparent sharpness. In what fundamental way does the mechanism of adjusting the aperture with a drum scanner differ from the software? Are we not with the software doing the same thing, i.e. adjusting edge rounding to match the average grain clump size?
Sandy King
Quote:
Originally Posted by
Tim Povlick
Back to the main point, scanning and film grain, (or whatever one wants to call it), the aperture is being set not to match simply the grain size of film, but the average size of the smallest grain. In Stochastic terms this would be the expected value of grain size. So I agree with what Aztek says, as long as one realizes it's the average grain size that set's aperture. Therefore one should not vary aperture while scanning, If one is set to 10 microns and along comes a dark area that is "clumped" at 55 micron, the 10 micron aperture will read the density properly.
Regards,
(West Coast) Tim
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
sanking
I have seen what seemed to me very significant grain reduction with software like Noise Ninja, without any apparent decrease in apparent sharpness. In what fundamental way does the mechanism of adjusting the aperture with a drum scanner differ from the software? Are we not with the software doing exactly the same thing, i.e. adjusting edge rounding to match the average grain clump size?
Sandy King
This is a little hard... it took me a while to understand this. I think the two processes are quite different from each other. Tim will have his own understanding, deeper in some ways than mine, but here goes. If someone has a better way to describe this, I'm all ears. I may also not be perfectly accurate in this description and feel free to correct me.
I believe Ninja blurs, at least that's what it did on my test. Maybe Sandy or someone else can fill in here if there is more to this... that's all I know and I don't mean to shortchange it.
The aperture is a sample, it isn't like this, but I imagine an opening to the sensor that's like a vertical shade - or shutter perpendicular to the drum. As the drum goes around, the sensor can see thru this shutter. One can widen the shutter or tighten it.
If you sample many times as the drum goes around, thru this opening, you get a series of samples, that make up the pixels of an image. A Premier has a 38,000 step stepper motor, with that many possibilities around a single circumference. It takes 8,000 of those steps and makes samples.
That's vertical. The drum can move over in increments of a16,000 of an inch at a time. It moves over a specific distance based on the ppi/aperture settings. It occurs to me I don't exactly know which one of these it chooses, but it must be the ppi if the aperture can oversample... If the slit that it looks thru is smaller than the RMS Granularity, the scanner will sample the same grain cloud more than once, creating an effect called grain anti-aliasing. If the slit matches the granularity, then you have a sharp scan with no ill effects. If the slit is larger then the image will be blurred.
It isn't a slit, its a circle in a rotating disc, it's just how I visualize it. There are usually two options that are "correct", one that will be grainy and sharp, and another where the grain is smoothed somewhat, but is still sharp. One can make a 1/8in x 1/8in sample and blow it up full size and watch the effects at different micron sizes. Differences are quite visible.
Here's a pic I made that I think illustrates the "slice" and the grain cloud it is looking at, and why I think this effect is occurring. I have a link to the comparison of how different micron settings affect the image here: http://eigerstudios.com/scancompareMicrons.html
I hope this helps...
Lenny
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Tim Povlick
the aperture is being set not to match simply the grain size of film, but the average size of the smallest grain. In Stochastic terms this would be the expected value of grain size. So I agree with what Aztek says, as long as one realizes it's the average grain size that set's aperture.
This makes no sense in purely mathematical terms. By definition, the expected value will never be the smallest grain size unless the grain is uniform in size. And in that case, talking about the "average grain size" is superfluous.
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Oren Grad
This makes no sense in purely mathematical terms. By definition, the expected value will never be the smallest grain size unless the grain is uniform in size. And in that case, talking about the "average grain size" is superfluous.
A little clumsy wording on my part. Edit "smallest" to "smaller" and it makes perfect sense to me.
I am trying to say one sets the aperture to match the average size of the grain. I was trying to exclude any large grain clumps from being included in the average.
Thanks,
Tim
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
Tim Povlick
While I would agree film grain clump size can be viewed as a Stochastic function, the is not the reason why. Can you elaborate on this? I checked "Probability, Random Variables, and Stochastic Processes" by Papoulis.
You're not likely to find it in a statistics text. This is about how film works. A stochastic process implies a level of randomness with an overlay of a guiding element. In this case the randomness is the distribution of silver halides in the emulsion and the guiding element is the exposure of image itself.
I'm just talking about metallic silver grain here. In color films dye couplers are used to replace the metallic silver grain clumps with dye clouds. So where I reference grain clumps you can substitute dye clouds and get the same basic meaning for color films.
Areas of low exposure (shadows) tend to capture the few photons that come their way at the surface levels of the emulsion. Areas of high exposure tend to capture photons throughout the depth of the emulsion. After processing, the resulting image show less graininess in the areas of low density and considerably more graininess in areas of higher density.
So far so good, yes? What makes graininess interesting is how it's formed. It's not just individual film grains. It's groups of grains, usually interlocking strands of metallic silver. These groupings form both in 2D and in 3D. That is, in the direction of the plane of the surface of the film, and in the depth of the emulsion. These groupings are commonly referred to as grain clumps. Note that overlapping of grain clumps as you look into the depth of the emulsion just makes them bigger. This is the view the scanner uses.
Finally grain clumps work together to create density in the film. There are at least two ways this happens. First, the size of the grain clumps increases. Second, the interstitial spaces between the grain clumps decreases. The net effect is that it's more difficult for light to pass through.
So... as grain clumps grow and become closer together they create the film's density. I believe I've read somewhere over the years that depending on the film, processing, and the image, that film grain clump size can vary a couple of orders of magnitude. Say from 1 to 100 microns.
To say that you can make any kind of a match between a single aperture and this range of grain clump sizes is, to me at least, quite a stretch.
Quote:
Originally Posted by
Tim Povlick
Back to the main point, scanning and film grain, (or whatever one wants to call it), the aperture is being set not to match simply the grain size of film, but the average size of the smallest grain.
Huh? The average of the smallest grain? I don't know what the means.
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Originally Posted by
Tim Povlick
In Stochastic terms this would be the expected value of grain size.
I don't follow you. You could use a statistical function to get an average or the mean maybe. Are you implying the RMS average grain size?
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Originally Posted by
Tim Povlick
So I agree with what Aztek says, as long as one realizes it's the average grain size that set's aperture.
I would at least not argue so much if that's what they said. But as I recall they leave out that pesky word "average."
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Originally Posted by
Tim Povlick
Therefore one should not vary aperture while scanning,
Should not? How about can not? I've never seen a scanner that would vary aperture during a scan. I wonder what kind of results you'd get if it did. Hmmm...
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Originally Posted by
Tim Povlick
If one is set to 10 microns and along comes a dark area that is "clumped" at 55 micron, the 10 micron aperture will read the density properly.
I disagree, but that's an argument for a different time and place. This dive into the rat hole is probably driving the OP crazy and isn't helping him much if any.
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Originally Posted by
Tim Povlick
Attached is an intentionally "bad" scan I did with the Premier on Ecke 25, 4K dpi and 8 micron ap. The light and dark areas show the same general "grain size", at least to my eyes.
What can one say to that? The laws of physics dictate that the grain clump sizes and distances must be different. Just because you can't see it doesn't mean that the scanner can't see it.
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Originally Posted by
Tim Povlick
FWIW I have worked with the folks at Aztek and found them to be straight talkers. This from an EE of 30 years experience that includes designs using PMT's.
I'm not saying they are bad people. I'm just saying that some of their marketing hype is bad physics. I'm also just pointing out that people shouldn't believe all the marking hype they see -- just because somebody printed it doesn't make it fact. All marketing hype regardless of source should be taken for what it is -- an attempt to persuade you to buy something. Marketing hype is seldom an appeal to logic. It most often is an appeal to your emotions.
So don't believe everything you read or hear. Including what you read and hear from me. Trust, but verify.
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Re: side by side comparison... large print digital back VS 4x5 color film
It sounds like there are many parallels to digital audio at work here, but with some optical twists. In essence we are talking about the fundamentals of digital sampling. In the digital audio world an anti aliasing-filter cuts out the garbage that is out of the range of the sampling frequency. This reduces noise that would be introduced by audio signals above the sampling frequency. It seems the aperture of a scanner serves the same purpose, at least it appears so from the scans Lenny posted a link to.
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Originally Posted by
Lenny Eiger
It moves over a specific distance based on the ppi/aperture settings. It occurs to me I don't exactly know which one of these it chooses, but it must be the ppi if the aperture can oversample... If the slit that it looks thru is smaller than the RMS Granularity, the scanner will sample the same grain cloud more than once, creating an effect called grain anti-aliasing. If the slit matches the granularity, then you have a sharp scan with no ill effects. If the slit is larger then the image will be blurred.
Are drum scanners oversampling up to the mechanical limits of the machine (38,000 samples for every 1/16,000th of an inch)? Where the aperture is determining the frequency of oversampling by controlling the physical size of the sample area?
Doesn't the scanner have to be scanning every grain more than once or it would not be able to decipher individual grains. At a minimum, you must be taking samples at twice the frequency/size of the smallest grain you would like to render accurately, correct?
Wouldn't a higher bit depth substantial increase the accuracy of scanning? 8-bits is only 256 possibilities. That is not very many in the digital sampling world. 16-bit is 65,536 possibilities. Shouldn't scanning at a higher bit depth lower the noise within the sample, as well?
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Re: side by side comparison... large print digital back VS 4x5 color film
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Originally Posted by
willwilson
Are drum scanners oversampling up to the mechanical limits of the machine (38,000 samples for every 1/16,000th of an inch)? Where the aperture is determining the frequency of oversampling by controlling the physical size of the sample area?
You're getting a little over my pay grade here, but in recent conversations about this, I believe the words "choose 8000 of these" were used. In the past, Phil mentioned that he could have supplied a 38,000 ppi scanner, but chose to do 8,000 as that was the limit of his optical resolution and he wanted to deliver "real" data.
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Originally Posted by
willwilson
Doesn't the scanner have to be scanning every grain more than once or it would not be able to decipher individual grains. At a minimum, you must be taking samples at twice the frequency/size of the smallest grain you would like to render accurately, correct?
I believe this refers to something different - frequency, size, vs number of samples of the same area. Further, I asked Phil what he thought of the Nyquist theorem and whether it applied to his scanning engineering. To paraphrase it politely, he said, "No."
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Originally Posted by
willwilson
Wouldn't a higher bit depth substantial increase the accuracy of scanning? 8-bits is only 256 possibilities. That is not very many in the digital sampling world. 16-bit is 65,536 possibilities. Shouldn't scanning at a higher bit depth lower the noise within the sample, as well?
I don't know the numbers for every scanner but they do vary. The older ICG's, I believe - don't quote me, did only 12 or 15 bits, etc. The Premier does full 16 bits. Since I am not clear on what causes noise in a drum scanner, I can't really answer your question. I might check in with Aztek on this.
Lenny
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Re: side by side comparison... large print digital back VS 4x5 color film
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Originally Posted by
Lenny Eiger
I believe this refers to something different - frequency, size, vs number of samples of the same area. Further, I asked Phil what he thought of the Nyquist theorem and whether it applied to his scanning engineering. To paraphrase it politely, he said, "No."
First of all, it's not a theorem, it's a mathematical property associated with analog to digital and digital to analog conversion.
If it doesn't apply, then there are a few possibilities:
His equipment is sensitive enough that it's capable of resolving smaller entities than the grains of film, and therefore is already beyond the Nyquist limit.
It's nowhere near the Nyquist limit.
It's magic.
You misunderstood his response.
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I don't know the numbers for every scanner but they do vary. The older ICG's, I believe - don't quote me, did only 12 or 15 bits, etc. The Premier does full 16 bits. Since I am not clear on what causes noise in a drum scanner, I can't really answer your question. I might check in with Aztek on this.
More bits will improve the precision of the analog to digital conversion, and make quantization errors smaller. So it should definitely lower the noise introduced through quantization error, if nothing else.
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Re: side by side comparison... large print digital back VS 4x5 color film
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Originally Posted by
willwilson
Doesn't the scanner have to be scanning every grain more than once or it would not be able to decipher individual grains. At a minimum, you must be taking samples at twice the frequency/size of the smallest grain you would like to render accurately, correct?
I think what you're looking for is that the smallest grains the laser can reliably resolve are 2x its wavelength.
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Re: side by side comparison... large print digital back VS 4x5 color film
Quote:
Originally Posted by
willwilson
Doesn't the scanner have to be scanning every grain more than once or it would not be able to decipher individual grains. At a minimum, you must be taking samples at twice the frequency/size of the smallest grain you would like to render accurately, correct?
A drum scanner makes perfectly square pixels that are a single uniform color. A drum scanner can not decipher individual grains. They are far too small, and almost fractal in nature. Once again, see Tim Vitale's excellent paper on the topic.
Scanners can not render grain accurately. But they do not need to.
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Re: side by side comparison... large print digital back VS 4x5 color film
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Originally Posted by
Rakesh Malik
First of all, it's not a theorem, it's a mathematical property associated with analog to digital and digital to analog conversion.
Actually, it is a theorem. See "Discrete Signal Processing," Oppenheim & Schafer.
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Re: side by side comparison... large print digital back VS 4x5 color film
Oops, I thought it was a property... thanks for the correction!
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Re: side by side comparison... large print digital back VS 4x5 color film
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Originally Posted by
Bruce Watson
You're not likely to find it in a statistics text. This is about how film works. A stochastic process implies a level of randomness with an overlay of a guiding element. In this case the randomness is the distribution of silver halides in the emulsion and the guiding element is the exposure of image itself.
Actually a Stochastic process can be completely deterministic.
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Originally Posted by
Bruce Watson
To say that you can make any kind of a match between a single aperture and this range of grain clump sizes is, to me at least, quite a stretch.
I don't follow you. You could use a statistical function to get an average or the mean maybe. Are you implying the RMS average grain size?
I would at least not argue so much if that's what they said. But as I recall they leave out that pesky word "average."
Should not? How about can not? I've never seen a scanner that would vary aperture during a scan. I wonder what kind of results you'd get if it did. Hmmm...
I do not see an advantage in varying the aperture during scanning. The down side is now the sampled values represent different sized samples from the film, placing this data into a fixed 2D array of pixel elements doesn't seem correct. In thinking about this I am of the opinion fixed aperture is the way to go. Thanks for your explanation of grain and grain clumping, this is very interesting and film is certainly different from fixed array CMOS / CCD arrays in this regard.
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Originally Posted by
Bruce Watson
So don't believe everything you read or hear. Including what you read and hear from me. Trust, but verify.
Agreed and thanks for the interesting discussion. I think our biggest challenge is getting the silver exposed to interesting subjects and developed correctly (at least for me).
Best Regards,
Tim