Multi Pass Scanning?

[Robert Lai]

Multisampling:
If you use curves a lot to bring up shadow detail, you will notice a benefit to multi-sampling. This is especially true with dense areas in slides, but I've also seen it with negatives. I noticed this with night-time scenes taken with the camera on a tripod. I use a Nikon Coolscan 5000 for scanning.

When I increased the shadow details using curves, the 1X multisampling scan looked like a snowstorm in the shadows. 2X was better in having much less noise. 4X seemed optimum. Beyond this, there didn't seem to be any major benefit over 4X from 8X or 16X multisampling. These are my observations from scanning Kodachrome and Velvia 50. It also held up for Fuji Acros 100 B&W negative film.

Vuescan multiexposure:
VueScan also has a Multiexposure feature to help improve shadow details from slides. The first scan is at normal exposure. The second scan is at a longer exposure time to dig out shadow details. Vuescan then performs an HDR type merge to give you a result with improved shadow detail without blown highlights. This seeming godsend has some downsides.

If you do too much multisampling, each pass takes so long that the film has time to shift. Mis-registration between the two images causes a slight degradation of fine detail compared to a straight scan, when viewed at 100% or greater magnification on screen. For that reason, if doing multiexposure, I try not to multisample beyond 4X.

The other problem is with negatives. The second longer exposure pass when tone-inverted to convert the negative into a positive image, gives better highlight detail. It doesn't improve shadow detail.

I mentioned these points to Ed Hamrick. As of version 8.4.48 he modified the program so that Vuescan will "[FONT=Comic Sans MS, Arial]Only do multi-exposure if scan will benefit".

It should be noted that Silverfast AI Studio also has a multiple-exposure option, in which the number of scan passes can be adjusted from 1-9. However, I do not have experience with this program, since I'm unwilling to pay $460 for the version that drives the Nikon Coolscan 5000.
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[PATB]

Couldn't find any difference between multi-pass (3-4x) and single pass with my Nikon Coolscan V ED/Vuescan, except it takes forever to scan. This is with Provia 400x/100f and negatives. So I only do a single pass.

 

[ffttklackdedeng]

16x multipass scanning (Vuescan) of silver based b&w films on my Coolscan V definitively improves the scan regarding the grain aliasing issue. Bad idea to remove this feature imho.

 

[RayPA]

16x multipass scanning (Vuescan) of silver based b&w films on my Coolscan V definitively improves the scan regarding the grain aliasing issue. Bad idea to remove this feature imho.

I agree. I use vuescan and also use the multi-pass option with my KM Scan Elite Scan 5400 II. I've had the scanner for a couple years now, and got it to replace an Epson flatbed. I've recently been going back over the old Epson flatbed scans (non-multipass scanner) for printing, and at close inspection, at high-magnifications, I'm seeing all kinds of scanning artifacts that I'm just not seeing on the KM. It could be a flatbed vs dedicated film scanner issue (I honestly don't know), but I'm not turning off multi-pass any time soon.

On the whole, I agree that there might not be much visual difference, and I'm sure having a tuned front-end process (exposure and developing) helps with assuring quality scans. After all, a well exposed and developed roll of film should scan nicely on everything from a flatbed to a drum scanner, but I think that if you have plans to print (particularly big prints), you probably want a multi-pass capable scanner, and you probably want to use that feature.


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[patrickhh]

I'm using 16x multi scan all the time. I admit that it might be total overkill, but I play around a lot with postprocessing, so I want to have all available image data in the scan.

 

[summicron2020]

I'm really surprised that most of you don't see a difference with the multipass scanning. It really helps with noise when scanning pushed film. I see a difference even with Tri-X and HP5+ rated at 400 when I use 16x scanning. Makes a huge difference for me with Delta 3200. I have the NIkon Coolscan 5000ED. I may start using Vuescan for its ability to get the Epson 4990 to do multipass scanning.

 

[lex]

i run a coolscan 4000ed with viewscan. recently, after being frustrated with the quality of my bw silver scans, i started using the the multiple exposure/pass feature. i set my sampling at 2 so with 2 passes i figure i get 4x sampling. i noticed and immediate improvement in my bw scans. less grain aliasing and more detail in the shadows...