How to beat 'aliasing' when scanning.....

....so modern colour negative film in particular is often finer grained (than it seems to be when we see our scanned colour negative images) as it could be the "grain is smaller than the sensor used to scan it"....leading to artefacts we call aliasing.....(no, I didn't make this up, this was what Ron Mowrey - ex Kodak engineer guru and all round great guy) said in an interview on Inside Analog Photo Radio some time back.......

so how do we beat or minimize aliazing when scanning colour negative? (with drum scanning in particular as is my case)

I'm looking at scanning at different resolutions (up to the max 5000 dpi my ScanMate 5000 yields for any given size) but this leads to massive massive files....is this the solution or am I way off the mark? aside from always scanning at 16-bit RGB I cant think of any other variable.....

Something else I'm thinking is if you are going to scan film and then do your thing for Editorials in magazines and what have you I'm thinking it must always be best to overexpose colour negative film to minimize noise etc.....assuming what we all know to be the fact that to lighten a dark area will start to throw up grain and crap as opposed to darken an area which starts 'forgiving' and 'covering up' so to speak......

sperera said:

so how do we beat or minimize aliazing when scanning colour negative? (with drum scanning in particular as is my case)

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Aliasing is a side-effect (read: by-product) of the analog to digital conversion which takes place during scanning.

To combat this, most modern scanning software offers at least one method of anti-aliasing. Silverfast offers two methods.

Im pretty much stuck with ColorQuartet for my ScanMate 5000....I think its a great programme so Im wondering what I can do about it all.....

tgphoto said:

Aliasing is a side-effect (read: by-product) of the analog to digital conversion which takes place during scanning.

To combat this, most modern scanning software offers at least one method of anti-aliasing. Silverfast offers two methods.

Click to expand...

I've never actually had an instance of grain aliasing using my ColorGetter 3 Pro drum scanners. Never seen it from B&W, never seen it from color negative. It's possible that this is due to scanning one spot at a time vs. scanning a line at a time. IDK.

That said, you can decrease the effects of grain in a drum scan by opening up your aperture a setting.

Before you accept that as some sort of magic bullet, do some testing. Scan the same piece of film twice with the *only* difference being the aperture. Then make two prints (no sharpening for either file), one from either file. Make these small sections taken from what would have been the full size print. Put these two prints up on a wall side-by-side under the same lighting.

Then and only then evaluate the effect. Tell us what you see. Get some people who don't know jack about photography or printing to look at them both and tell you which one they like best. Don't tell them a thing about it, just ask them to make a preference. Don't even ask them why they chose what they chose, because it really doesn't matter -- they like what they like when they see it.

It's a very instructive exercise that all drum scanner operators should do at least once.

doesnt' color film (both slides and neg) use dye???? there should be no grain! yes grain in silver halide materials (like B&W) but look under high magnification... should be no "grain" in color materials

Actually Bruce, on advice from another user I have been scanning with the aperture more open as you say ans its making a difference....it made a big difference when scanning Fuji Pro 400H the other day which left me cold on the first attempt......

I will definitely do that test you so kindly note....

Bruce Watson said:

I've never actually had an instance of grain aliasing using my ColorGetter 3 Pro drum scanners. Never seen it from B&W, never seen it from color negative. It's possible that this is due to scanning one spot at a time vs. scanning a line at a time. IDK.

That said, you can decrease the effects of grain in a drum scan by opening up your aperture a setting.

Before you accept that as some sort of magic bullet, do some testing. Scan the same piece of film twice with the *only* difference being the aperture. Then make two prints (no sharpening for either file), one from either file. Make these small sections taken from what would have been the full size print. Put these two prints up on a wall side-by-side under the same lighting.

Then and only then evaluate the effect. Tell us what you see. Get some people who don't know jack about photography or printing to look at them both and tell you which one they like best. Don't tell them a thing about it, just ask them to make a preference. Don't even ask them why they chose what they chose, because it really doesn't matter -- they like what they like when they see it.

It's a very instructive exercise that all drum scanner operators should do at least once.

Click to expand...

williamtheis said:

doesnt' color film (both slides and neg) use dye???? there should be no grain!

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The dye clouds are made from dye couplers linked to the metallic silver during the process. Then the silver is bleached and fixed out, leaving nothing behind but the dyes. So you are right, there is no grain. What there is, is graininess. Because the dye clouds are pretty darn good representatives of the metallic silver that's been removed from the film. The dye clouds are translucent, but not transparent, so the graininess remains.

If you want an in-depth discussion of the structure of film, you'll be hard pressed to do better than Tim Vitale. More than any one person could ever want to know about what film actually does, and how it interacts with scanning. Enjoy!

Hi

I noticed that the version of this document which Bruce has linked too seems to be older than one I have ... so I've put that on Google Documents here if anyone is interested in a later version (I don't see much in changes there).

You may also find this good reading

If I may quote some pertinent statements from that:

Fuji 'Pepper Grain'The Mystery Resolved
update Blowing Bubbles

By: Roger Smith

In August of 2001 I replaced my Canon FS2710 35mm film scanner with a Minolta Dimage Scan Dual II, a 2820 ppi film scanner. I soon noticed that, while the Minolta was sharper than the Canon, it had a tendency to emphasize dirt and flaws on my slides and negatives. I also noticed, as had Michael Reichmann and Nick Rains before me, that viewing light areas in scans at high magnifications showed countless random black specks.

As a scientific photographer, I have access to a selection of high-power microscopes, so I decided to have a closer look at some of the offending slides. Under a microscope set for 400x magnification, I could clearly see that the offending speckles were actually microscopic bubbles embedded in the film. Fig. 3 is from a small area inside the "8" of the previous figures, taken with a Nikon Coolpix 995 digital camera on a Leitz microscope.

Focusing carefully up and down on the slide I isolated the bubbles in the scratch-resistant layer just outside the emulsion layer not in the plastic base as I might have expected.

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Given that a drum scanner may have a much narrower depth of field than a Coolscan (despite the discussions of just how narrow the DoF of a Nikon Coolscan is), thus focus may be able to reduce or eliminate this feature of the film.

Note: I believe that you can see the dye clouds in the last photomicrograph.

*For thirty years Roger Smith has been the scientific photographer in the Department of Biology, University of New Brunswick, in Fredericton, New Brunswick, Canada.

sperera said:

....so modern colour negative film in particular is often finer grained (than it seems to be when we see our scanned colour negative images) as it could be the "grain is smaller than the sensor used to scan it"....leading to artefacts we call aliasing.....(no, I didn't make this up, this was what Ron Mowrey - ex Kodak engineer guru and all round great guy) said in an interview on Inside Analog Photo Radio some time back.......

so how do we beat or minimize aliazing when scanning colour negative? (with drum scanning in particular as is my case)
..

Click to expand...

I will have to defer to the judgment of someone like Bruce Watson for a specific answer with drum scanning but for certain the skill of the operator makes a huge difference. A couple of years ago I had the same ASA 400 medium format color negative scanned with a Howtek 4500 and 6500 to compare with a scan of the same negative I made with a Creo Eversmart Pro. I don't remember the details of how the scans were made with the two Howtek drums scanners but the one made with the 6500 was *very* grainy, almost pointillistic, while the one made with the 4500 was almost grain free and just as sharp. And the scan I made with the Eversmart Pro, fluid mounted, was also almost grain free, and just a sharp as 4500.

With several CCD type scanners I have observed that grain is nearly always optimized by the use of fluid mounting. Also, I think that grain aliasing tends to take place with scans in the 2000 dpi - 2800 dpi range with CCD scanners. I never see them at higher and lower resolution.

Sandy King

sanking said:

...
Also, I think that grain aliasing tends to take place with scans in the 2000 dpi - 2800 dpi range with CCD scanners. I never see them at higher and lower resolution.
...

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Same IME too. My Minolta Dual Scan III (2800 or so spi) gives me hard times with grain aliasing often...

sperera said:

Actually Bruce, on advice from another user I have been scanning with the aperture more open as you say ans its making a difference....it made a big difference when scanning Fuji Pro 400H the other day which left me cold on the first attempt......

I will definitely do that test you so kindly note....

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A couple of us mentioned that opening up the aperture to 10-15 microns makes a big difference in grain appearance. Fluid mounting is also a good grain equalizer.

Sandy

sanking said:

A couple of years ago I had the same ASA 400 medium format color negative scanned with a Howtek 4500 and 6500 to compare with a scan of the same negative I made with a Creo Eversmart Pro. I don't remember the details of how the scans were made with the two Howtek drums scanners but the one made with the 6500 was *very* grainy, almost pointillistic, while the one made with the 4500 was almost grain free and just as sharp.

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anything like this?



I have observed this on other drum scans in the past, this just happens to be an example.

I am interested to understand this phenomenon

pellicle said:

Sandy
anything like this?

I have observed this on other drum scans in the past, this just happens to be an example.

I am interested to understand this phenomenon

Click to expand...

Yes, pretty much like the file you posted. I am told by the operator who made the better scan that the reason for the pointillistic look was because the other operator used a very small aperture in an effort to obtain maximum resolution. His comment was you can open up the aperture a bit and get equivalent sharpness but less obnoxious grain.

Sandy King

sanking said:

Yes, pretty much like the file you posted

.... His comment was you can open up the aperture a bit and get equivalent sharpness but less obnoxious grain.

Click to expand...

thanks for the addition it was interesting ... just got some 6000dpi stuff back from a X-5 ... I'm betting that it has a larger equivalent aperture.

the X5 scans were nice scans btw

pellicle said:

thanks for the addition it was interesting ... just got some 6000dpi stuff back from a X-5 ... I'm betting that it has a larger equivalent aperture.

the X5 scans were nice scans btw

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How do you find the scans from the X5 compare to the old 848 for example?

David Luttmann said:

How do you find the scans from the X5 compare to the old 848 for example?

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sadly I can't compare them ... if you have an 848 I can send you a strip of 35mm (that was used in the X5 compare and you could scan it

[In case mrred is reading this I'm still wondering if I'll ever see those strips again to complete that test]

pellicle said:

sadly I can't compare them ... if you have an 848 I can send you a strip of 35mm (that was used in the X5 compare and you could scan it

[In case mrred is reading this I'm still wondering if I'll ever see those strips again to complete that test]

Click to expand...

Sadly, I don't own on...but I do have access to one for regular use. Well, if you ever get it back, send me a PM.

Thanks so much for the article pdf.....can we discuss what is meant by this in practice:

tjvitale@ix.netcom.com page 21 510-594-8277 Tim Vitale (c) Use with permission only

Art of Drum Scanning -- No Film Grain with Higher Image Digital Resolution
Often, a drum scanner operator will choose a pixel pitch (ppi) that is much smaller than the aperture. Thus, the uniformly digitized RGB value captured at a fixed aperture is spread over a larger number of pixels, each smaller in area than the size of the original aperture used for capture. An example would be the operator choosing a 12 um aperture (113 um2 round) because it eliminated film grain, and then use a 5000 ppi pixel pitch, that had an equivalent feature size of 5.0 um. This setup would yield 5 pixels (22.5 um2) per aperture area (113 um2). Each of the 5 pixels is given the RGB value created by the A-D converter from the light intensity measured through the aperture by the PMT. The greater the pixel population, all without the noise from film grain, allows a given image to be enlarged more than the equivalent raw film, given its obvious film grain.
Drum Scan: Aperture
Aperture is the opening at which the analog PMT (photo- multiplier tube) measures the intensity of light coming from the film. The analog light value measured by the PMT is converted into a digital RGB value in the analog- to-digital converter (A-D), commonly 12-bit native, for most drum scanners.
If the scan aperture is approximately equal to the perceived grain size, (a value determined from the experience of the operator) the noise of the “variations” across individual “film grains” is eliminated when the average density for that region is measured by the PMT.
If the pitch of the image pixels (ppi) is set slightly larger than, or equal to, the aperture size, the uniform density of the light through the aperture is represented by an area of uniform digital image density (D) in the final digital image pixel, on a one-to-one basis. The measured image density for the pixel -- minus the image noise introduced by the variations across the film grain -- is rendered as a uniform RGB value for each individual pixel. This eliminates film grain on the capture level.

In this example, the 35 mm B&W film image (12 um = 2117 x 3176 pixels) would enlarge well to a 7 x 10 print, at the equivalent of 300 dpi or 6 lp/mm. On the other hand, the drum scanned digital version described above could be enlarged to a 16”x 25” print, 5 times larger, with individual pixels printed at 300 dpi, the average human perception.
Balancing aperture and pixel pitch is the art of drum scanning. This sort of graceful lying is common in drum scans. Note that these procedures remain highly prized; based on the high monetary value these scan fetch in the marketplace, even in the presence of flatbed scanners with equal or greater resolution.

Bruce Watson said:

So you are right, there is no grain. What there is, is graininess.

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I'm going to share some experience. Not book smarts... Hopefully this ads to the discussion.

I shoot a lot of 4x5 on color positive film. At the moment I'm exclusive to Ektachrome E100VS as I got a great deal on a lot of it. When shooting pinhole, I notice no grain whatsoever, period, end of story, on Ektachrome and Provia and Velvia and Astia. Using my studio 4x5, well now that's where you start to see differences. There does appear to be, what I'll call a loss of details, on the E100VS and the Velvia and the Provia. The details appear in situations where there's a lot of color variation in a small space, which leads me to think this is the aliasing in action. When you have pixel to pixel changes that are abrupt and differing ends of the color spectrum and it appears to be intermixed, then there is loss of data and you're only picking up the color that the equipment viewed or the predominate color or an averaged color but I doubt there is dynamic averaging going on in the scanner process.

Anyway, all this above changes when using two films in particular. Ektachrome E100G and Fuji Astia. These are the finest grain color films that exist. I was told they were made pretty much specifically for scanning and image setting. When I line E100VS up against E100G, the E100G looks far more refined. And only ever so slightly less color saturation. I would buy exclusively E100G, but I found it difficult to source when I was buying my film for the season.

Hi

Perry Way said:

I shoot a lot of 4x5 on color positive film. At the moment I'm exclusive to Ektachrome E100VS as I got a great deal on a lot of it. When shooting pinhole, I notice no grain whatsoever, period, end of story,

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so, what about with a lens? Do you see grain there then? I'm asking this because your words seem to imply that you see no grain with pinhole and thus to me suggest that you do see it with lenses ...

I have E100G 120 format sitting there in the fridge and now i feel like using it!!!! hahahha

Perry Way said:

I'm going to share some experience. Not book smarts... Hopefully this ads to the discussion.

I shoot a lot of 4x5 on color positive film. At the moment I'm exclusive to Ektachrome E100VS as I got a great deal on a lot of it. When shooting pinhole, I notice no grain whatsoever, period, end of story, on Ektachrome and Provia and Velvia and Astia. Using my studio 4x5, well now that's where you start to see differences. There does appear to be, what I'll call a loss of details, on the E100VS and the Velvia and the Provia. The details appear in situations where there's a lot of color variation in a small space, which leads me to think this is the aliasing in action. When you have pixel to pixel changes that are abrupt and differing ends of the color spectrum and it appears to be intermixed, then there is loss of data and you're only picking up the color that the equipment viewed or the predominate color or an averaged color but I doubt there is dynamic averaging going on in the scanner process.

Anyway, all this above changes when using two films in particular. Ektachrome E100G and Fuji Astia. These are the finest grain color films that exist. I was told they were made pretty much specifically for scanning and image setting. When I line E100VS up against E100G, the E100G looks far more refined. And only ever so slightly less color saturation. I would buy exclusively E100G, but I found it difficult to source when I was buying my film for the season.

Click to expand...

This thread is a bit old, but I gotta keep trying...

Is anyone familiar with a Scanmate 3000 drum scanner? It seems to have only two apertures which are automatically set depending on the scanning resolution (3000 dpi being the highest). Could it be detrimental with regards to grain with some films?

3000 dpi: too low resolution for reducing the grain aliasing, expecially if you can choose just few apertures.

There are 12.000 dpi drum scanners using 25 apertures: they're many steps over to reduce grain aliasing and noise (apart a far higher detail).

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