Max scanning resolution

[Songyun]

Maybe this has been asked before, some higher end scanner provides very high resolution, but is it really needed? I mean, if the lens used to take the picture has resolution 80 lpmm, which is 80X25=2000 lp inch, if you scan over 4000 dpi, it shouldn't provide more details, am I right?

[Bruce Watson]

You are right. This has been discussed many times before, including on this site. Search around and you'll find it. This very question was asked earlier this year I think.

It's a simple question with quite complex answer(s). The search function is your friend.

[Songyun]

I would like to search for that, can you suggest what key words to search?

[Ben Syverson]

If you're getting 80 lp/mm, odds are you're not shooting LF... most LF lenses top out much lower than that, and those that don't tend to be stopped down enough (f/22, 32) to erase their advantage.

[Bruce Watson]

I would like to search for that, can you suggest what key words to search?

Oh, I dunno. How about Max scanning resolution (http://www.largeformatphotography.info/forum/search.php?searchid=2935873)? That'll turn up this thread (http://www.largeformatphotography.info/forum/showthread.php?t=47371&highlight=max+scanning+resolution) anyway.

There are few questions one can ask that haven't already been answered. Happens to us all. Search is your friend.

[bernal]

Maybe this has been asked before, some higher end scanner provides very high resolution, but is it really needed? I mean, if the lens used to take the picture has resolution 80 lpmm, which is 80X25=2000 lp inch, if you scan over 4000 dpi, it shouldn't provide more details, am I right?

Hi Songyun,

In my opinion, regardless of how much resolution you get at the capture stage, one would be wise to scan at the highest resolution the scanner is capable of. Capturing and scanning are two different things. Scanning resolution dictates what size you can print at. The higher the resolution, the bigger you can print. Maybe you don't need big prints at present time, but what if you do down the road? Scan once, print many sizes.

bernal

[Lenny Eiger]

Maybe this has been asked before, some higher end scanner provides very high resolution, but is it really needed? I mean, if the lens used to take the picture has resolution 80 lpmm, which is 80X25=2000 lp inch, if you scan over 4000 dpi, it shouldn't provide more details, am I right?

Numbers don't tell the whole story. There are flatbeds vs drums, which scan very differently and need to be treated differently in the post-scan stage. I think the resolution numbers fall apart when you compare 4x5 to 8x10. If you scan them at the same resolution you still get a better print from the 8x10. (Annoyingly.) It isn't all about resolution...

One fellow suggested that the max one could get off an 810 is 72 mgpxls. His numbers for the lens and all may be right, I can't dispute it with my limited knowledge of optics, but the results on the prints are clearly far in excess of that.

I prefer to get plenty of extra pixels just in case the output needs to be larger. I don't like to re-scan, and most of my clients don't like to pay for a second scan, much less do all the photoshop work again for a larger print. I usually scan larger. But there are limits, I don't usually scan an 8x10 to a 24 Gig file. It just isn't needed unless to want to make a huge print, say larger than 10 feet.

There is certainly no reason to scan at a higher resolution that the optical resolution of the scanner. For my drum, that's about 8,000 ppi, for a consumer flatbed, that's in the 2000-2400 range, the lower, in my opinion.

Lenny

[Gordon Moat]

When what you scan compares to what you see on the film through a loupe, then you are at the maximum usable scanning resolution. To go beyond that can sometimes help tonal transitions and large areas of colour. The downside is that scanned file sizes can become quite large, which will slow down the entire process.

One work-flow method is Scan Once, Output Many (SOOM). To do that, you always scan at the maximum hardware scanning resolution of the scanner. Then you archive that result. When you need to send out an image file, or have an image printed, you size the file for the best output match. This can be efficient with high end scanners, but not might be practical with more consumer oriented gear due to their slower speed of operation.

Ciao!

Gordon Moat Photography (http://www.gordonmoat.com)

[Songyun]

Oh, I dunno. How about Max scanning resolution (http://www.largeformatphotography.info/forum/search.php?searchid=2935873)? That'll turn up this thread (http://www.largeformatphotography.info/forum/showthread.php?t=47371&highlight=max+scanning+resolution) anyway.

There are few questions one can ask that haven't already been answered. Happens to us all. Search is your friend.

Bruce, thanks a lot, now I have something to read first. :)

[Tyler Boley]

Hi Songyun,

...Scanning resolution dictates what size you can print at. The higher the resolution, the bigger you can print...

bernal

Not to be argumentative, but I actually slightly disagree, perhaps it's only rhetorical. The preferred scanner resolution (difficult to actually wrap up in a single term like that) has to do with how much of the detail on the film written to file is desired. This also is difficult to apply a singe term to, because what constitutes "good", or useful detail? Do you want to resolve the optical image, or down to the grain? Rarely the same.
Anyway, accurate description of the film character, including the grain, requires scanner specific settings, rarely not more than 4000ppi in my experience, usually less. Now we have the issues of ccd vs pmt, and aperture... too much for now...
Anyway, describing the film, and print size, are separate issues.

Then, over particular print sizes, more ppi is required to hit printer resolution than is required for accurate film description at the scanner stage. So non-descriptive pixels are going to be manufactured one way or another, and this needn't be a bad thing, in fact it's more often than not a simple unavoidable fact.
Now the question becomes how to get there... make a bigger scan then necessary for the film? Is this done with true optical ability of the scanner or oversampling? Res up various methods, Photoshop or plugins? Or simply let the printer driver/RIP make the larger matrix of dots how it sees fit?
Often we are making scans far bigger then what is necessary to define the detail yielded by our lenses on the film. This may be the best way to get to the desired print sizes, sometimes it makes no difference in my experience. I'm only trying to point out that resolving film image and getting to print sizes are separate issues.
Tyler
http://www.custom-digital.com/

[Leonard Evens]

It should be kept in mind that the resolution resulting from multiple steps in the process is LESS THAN that of each of the steps alone. That means that even the best possible scanner will reduce the resolution you end up with, but that may be only very slightly if the scanner is good enough.

There are two popular rules of thumb for calculating the combined resolution which are used in practice. If you start with the component resolutions about equal, then either rule tells you the resulting resolution will be significant reduced. When you scan a large format negative or transparency, there are at least three resolutions: that of the lens, that of the film, and that of the scanner. The first two will already reduce the resolution to something less than 50 lp/mm (perhaps much less). So you want the scanner to resolve significantly more than that if possible so that the scanning step makes only a small further reduction.

4800 ppi is the same as about 189 pixels per mm. But you have to divide that in half because you want LINE PAIRS, each of which requires two pixels. That gets you down to about 94 lp/mm. That would be large enough not to affect the final result enough to matter, if the scanner actually delivered that. Unfortunately, there is one more complication. The scanner rating tells you just how many pixels it collects without telling you the quality of those pixels in terms of resolving detail. Thus, a 4800 ppi scanner in reality might only deliver say 40 lp/mm. Scanners differ significantly in how close they come to providing the theoretical resolution the scanning rate would suggest. Typically, for example, a 4000 ppi scanner for 35 mm film will do better, for example, than a 4800 ppi scanner which can do large format. That is because it is easier to mainatin optical quality over the smaller format.

Unfortunately, if you scan at extremely high sampling rates, you get very large files, which require a lot of memory, a fast processor, and lots of storage space. So there are practical limits, as well as cost, in using a very high scanning rate. Also, you can improve the apparent sharpness of the image by various digital techniques. So unless you are making wall sized prints which you expect people to view from close up, you need not use such high resolution scanners. I am comfortable with what I've been able to get from my Epson 3200 scanner, at least for the present. I can produce a 16 x 20 print which will look sharp as long as the viewer stays at normal viewing distance. Some day I wlll get a 4800 ppi scanner, but I won't bother going beyond that.

But, if cost is no object, and you can manage the enormous files you would end up with, then get the highest scanning rate you can get, and make sure the optical quality of the scanner is high enough that you get something close to that scanning rate in practice. If you do that, the resolution you end up with will be determined primarily by the lenses and film you use, and you will have eliminated the scanner as a limiting factor in your work.

P.S. The high scanning rates provided by many consumer grade scanners are meant to be used with medium format or 35 mm. In practice you might not need to highest scanning rate for 4 x 5.

[Brian Ellis]

Oh, I dunno. How about Max scanning resolution (http://www.largeformatphotography.info/forum/search.php?searchid=2935873)? That'll turn up this thread (http://www.largeformatphotography.info/forum/showthread.php?t=47371&highlight=max+scanning+resolution) anyway.

There are few questions one can ask that haven't already been answered. Happens to us all. Search is your friend.

I don't remember anyone asking what camera to buy for their first LF camera - not today that is.

[Matus Kalisky]

In general I think it is rather simple. Even if you scan your film beyond expected resolution of your lens/film combination, it looks better in a large print as when you just extrapolate with some software. I will better add SOME information (even though it will be mostly film grain and random structures) than fully information-less extrapolation. I also think that scanner noise is easier to fight with if I do not have to enlarge it.

[SCHWARZZEIT]

There're several approaches, and some were already mentioned in this thread:

- Use the highest optical resolution of the scanner to get the most information out of the film. But at very high end scanners it can lead to extremly large file sizes without any gain in image detail compared to a lower resolution scan. So this approach might not be very practical in some cases.

- Calculate the resolution based on a 300-400 dpi print of the maximum size you think you'll ever want for this image. This is the most simple approach. Even if your image doesn't have that much information the print will look more natural with enlarged grain instead of interpolated pixels.

- Choose the resolution by the image detail on film. If you know you shot this image at f/22 you know that no matter how good your lens is diffraction will not give you more than 70 lp/mm. Knowing that the scanner and in fact all raster media resolve the image better in scanning direction than diagonal (45°) to that direction you should chose a resolution to let you capture the potential 70 lp/mm in diagonal resolution. For 70 lp/mm in scanning direction you need at least 3556 ppi, multiply this by the squareroot of 2 to make up for the diagonal loss and you have your input scanning resolution of 5029 spi. You might want to add a couple of spi to be on the safe side when it comes to sampling artifacts. An easier way to calculate a safe ball park figure is to take the resolution limit of your lens and film combination for that image in lp/mm multiply it by 75. In the diffraction limited f/22 example you would get 5250 spi. It's a large file, and you'll need a scanner that can optically resolve such detail but you can be sure there's no need to scan that film again for image detail. In many cases it's overkill compared to what might be really captured on film. For f/32 the number would be 3750 dpi and for f/16 7125 spi in case of diffraction limited performance.
The best large format lenses I tested could resolve just short of 100 lp/mm in the center on film at f-stops wider than 11 but at the expense of very soft corners.

-Dominique