Trying to understand scan resolution

[malligator]

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I am starting to scan film at home and I'm having a hard time understanding why my results look the way they do.

I had some Ektachrome slide film developed and scanned by Richard Photo Lab. I think it was the Noritsu scanner, but I can't remember. Anyway, the scans aren't that big. Maybe 2000x3000 with 4-6mb jpeg sizes. I'm not sure how big those will print, but I'd like to maybe try 11x14.

I scanned the same slide with my Pacific Image XAs at home at the max resolution (according to FilmScanner.info) of 4300. It looks good and is much bigger (4000x6000/44mb TIFF), but if I pixel peep to 400% the smaller image from RPL looks better...or at least sharper.

I pulled the XAs scan into Photoshop and cut it down to the same 2000x3000 and sharpened it a little (+20) in LR. When I do that it looks much more like the RPL scan.

What's going on here? Why doesn't the larger scan from the XAs look as good at its native size? Can I actually print it bigger (say 16x20)? Is it actually a better scan or is it just a bigger scan at a lower resolution?

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[Tom R]

First, have a look at the following link: https://www.scantips.com

This is an excellent resource for understanding "resolution" as well as computing optimal resolutions for various applications. I am pretty sure that you'll also find technical discussions about scanning positive versus scanning negatives and their relative affordances and drawbacks.

Off the top of my head, I see lots of moving parts here: comparing scans from different machines, Noritsu (which is probably using EZ-Scan software, etc.) and Pacific Image XA (which I use to create "contact sheets," (creating reasonable jpegs from batch scans)). For one thing, I suspect that 4300 in interpolated by the PA scanner's software and I am not sure how well such software approximations perform versus scans set to the "native" or supported resolutions provided by the scanner's manufacturer. I don't know if you performed any "filtering," such as Lanczos or bi-cubic, etc., when downsizing the image into Photoshop. And, I'm not sure that "sharpening" the image in LR might not add its own artifacts.

I am sure that we have numerous, and more knowledgable people in this Forum who might (and hopefully will) assist you. I, for one, will be interested in hearing what others may have to say on this topic as I scans lots of film (almost exclusively panchromatic, 35mm negatives, however).

Edited August 26, 2023 by Tom R

[malligator]

Thanks. About halfway through that site. Learning a lot, but it’s still going to generate a million questions—give or take. 

[Anbaric]

Generally, commercial labs apply some sharpening unless you ask them not to. Incidentally, the Noritsu is capable of much higher resolution scans than 2000x3000, so if you want to use lab scans to make big prints it's worth asking for something larger (though most labs charge extra for this).

[malligator]

6 minutes ago, Anbaric said:

Generally, commercial labs apply some sharpening unless you ask them not to. Incidentally, the Noritsu is capable of much higher resolution scans than 2000x3000, so if you want to use lab scans to make big prints it's worth asking for something larger (though most labs charge extra for this).

Yeah, the scans I got were “lab’s choice” scans. I could have gone one bigger for some extra cash. 

[hansvons]

16 hours ago, malligator said:

I am starting to scan film at home and I'm having a hard time understanding why my results look the way they do.

There are many reasons why home scans show an unsatisfactory quality/sharpness/resolution.

1. A 35mm film can only resolve so much. ISO 400 tends to be in the 2-3k realm, ISO 100 stocks like Delta 100 can resolve up to 5K, and the best cine colour negatives resolve approximately 4K in super 35mm, roughly 5K in FF. Any scanning that resolves higher is only more precise in noise. That means a 24MP/6K sensor is plenty enough for 35mm scans.

2. The medium you look at your scans is critical. How good is your screen? Do you look at the actual size, or does the viewing application scale the image? 

3. The scanner has a lens and a sensor, plus electronics, that manipulate the signal and create the output. How good are they? A professional 30k scanner has better optics and electronics than a 600k scanner. How good can the sensor/optics be in a relatively cheap scanner? Probably less than in a good DSLR for 4+ times the cost. That's why home scanners tend to introduce coloured noise, aliasing artefacts, show less colour fidelity, or are not dead sharp (check the grain).

4. How are the scaling algorithms designed to scale the images? Quite a few are out there, and they strongly influence sharpness, aliasing, etc. Because it's fast and sharp, linear is often used. But it introduces jitty lines. Linear/EWA is usually better, and so is Lanczos and others.

This brings me to this: if you own a DSLR, you will get much better scanning results with the camera, an excellent macro lens, a film holder, and a proper backlight than with any home scanner. It's not only the sensor, the DR, the lens, etc.; it's also the application in which you will edit the image. Light Room, Capture One, and other raw converters are designed to optimise the results for sharpness and fidelity. And they offer you many options to optimise the results in texture terms, from sharpening and structure to colour noise reduction, you name it. 

 

 

 

 

 

[malligator]

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On 8/27/2023 at 3:03 AM, hansvons said:

There are many reasons why home scans show an unsatisfactory quality/sharpness/resolution.

1. A 35mm film can only resolve so much. ISO 400 tends to be in the 2-3k realm, ISO 100 stocks like Delta 100 can resolve up to 5K, and the best cine colour negatives resolve approximately 4K in super 35mm, roughly 5K in FF. Any scanning that resolves higher is only more precise in noise. That means a 24MP/6K sensor is plenty enough for 35mm scans.

2. The medium you look at your scans is critical. How good is your screen? Do you look at the actual size, or does the viewing application scale the image? 

3. The scanner has a lens and a sensor, plus electronics, that manipulate the signal and create the output. How good are they? A professional 30k scanner has better optics and electronics than a 600k scanner. How good can the sensor/optics be in a relatively cheap scanner? Probably less than in a good DSLR for 4+ times the cost. That's why home scanners tend to introduce coloured noise, aliasing artefacts, show less colour fidelity, or are not dead sharp (check the grain).

4. How are the scaling algorithms designed to scale the images? Quite a few are out there, and they strongly influence sharpness, aliasing, etc. Because it's fast and sharp, linear is often used. But it introduces jitty lines. Linear/EWA is usually better, and so is Lanczos and others.

This brings me to this: if you own a DSLR, you will get much better scanning results with the camera, an excellent macro lens, a film holder, and a proper backlight than with any home scanner. It's not only the sensor, the DR, the lens, etc.; it's also the application in which you will edit the image. Light Room, Capture One, and other raw converters are designed to optimise the results for sharpness and fidelity. And they offer you many options to optimise the results in texture terms, from sharpening and structure to colour noise reduction, you name it. 

 

I appreciate the thoughtful response. Unfortunately I don't have any DSLR scanning hardware. I have a 2020 MacBook Air and the Primefilm XAs. That's the extent of my scanning setup. I'd be willing to buy the copy stand, film holder, etc. but I'm not sure I want to buy a digital camera for the sole purpose of scanning film.

 

[hansvons]

5 hours ago, malligator said:

but I'm not sure I want to buy a digital camera for the sole purpose of scanning film.

I can totally see this.

[jaapv]

Well, if you get for instance a refurb Canon 750D, about 350€ , a used 1.8/50 (80 €) and a light box/stand it is a lot cheaper and better quality than a prosumer level  scanner. Bonus: working  the image in LR is uncomplicated.

[irenedp]

I don't own a film Leica, and am no great expert in scanning, but I took it with some enthusiasm about three years ago with my old film cameras and an Epson V850 with Silverfast. The 35 mm negatives, from a Nikon F4, are nice but only decent in small sizes. The 6x4.5, from a Bronica ETRS are significantly better and could get decent results but the same images taken side by side with a Fuji GFX 100 were better. This test was done with Portra 400. The best -those are really good and comparable to digital medium format- come from my Linhof and a Flextight scanner. 

Flextights, from Hasselblad, are no longer made. Happens the same as with the legendary Heidelbergs. Second hand machines are tremendously expensive. 

The film camera I use most -maybe because it offers the best balance between ease of use and quality- is the Bronica (I use Ektar and Ektachrome). I have access to a Flextight from a friend, but am willing to look at the copy stand route. I guess the S3 -which has replaced the Fuji- could be a good alternative, although I don't have a macro lens. 

My take is that to obtain good results, everything matters: the size of the negative, the quality of the lenses, the grain of the film (100 ISO is notably better than 400... obviously) and the scanner used.

As a tip, if you have access to an educational institution, it's worth a try. For instance, at my old school, University of Brighton's lab, there's a couple of Flextights, although they don't have any drum one.

Looking forward to hear more about DSLR scanning experiences. This is a topic I am very much interested in. 

Edited September 2, 2023 by irenedp
typos

[250swb]

@irenedp the Epson is a good scanner for medium format but it's terrible for 35mm unless they are just a digital contact sheet. Personally I'd run it with the regular Epson Scan software as well. 

But a full frame digital camera with 24mp or more is a better route. This will copy 35mm film extremely well, but more megapixels are desirable if you copy negatives that aren't 2x3 format such as 6cmx6cm (1x1) as this involves some wasted space on a full frame sensor. There is plenty of advice for a simple setup already given. For myself I use a Nikon Z7, 60mm micro Nikkor, a cheap copy stand, a Kaiser Slim Lite Plano for a light source, and an old negative holder from a scanner or I make my own for medium and large format negatives.

Edited September 2, 2023 by 250swb