How much is enough?????

[ignatiusjk]

How much dpi is enough.Some scanners go as high as 12,800 some 6400 and less, but what is a good average dpi both in scanners and in printers.

[Daniel_Buck]

depends on what size film you are scanning, and what size output you want. In general though, things higher than 2400 (consumer scanners anyway) probably don't make much difference in image quality. Just because the scanner can scan at 12800, doesn't mean it's actually resolving that much detail.

[Norm Buchanan]

As Daniel says the resolution numbers can be misleading - much has been written here and elsewhere on this. Most people will recommend scanning at 2400dpi, which will allow lossless prints (at 360dpi) of 4x5 negs up to almost 20x24". I find if I need to either upsize or downsize a scan I get observably better results by scanning at 4800 dpi first. These are HUGE files though and it really depends on how picky you are.

[Greg Lockrey]

Look, many very excellent photographers already told you what you need. Try it, send your 4x5's to someone on the forum that is nearby to you that has the equipment that you are thinking about and have them make a print or two for you to see for yourself. It is hard to decide what your limits are too. You might well be another "Lenny Eigler" in need of very high end quality. 90% of us are frankly not. Especially about spending that kind of money.

[Bruce Watson]

How much dpi is enough.Some scanners go as high as 12,800 some 6400 and less, but what is a good average dpi both in scanners and in printers.

Terminology first. Scanners work in spi (samples per inch) and create files in ppi (pixels per inch). Printers print in dpi (dots per inch) and usually use many dots to make a pixel. What you send to the printer is a file in ppi then, for example you can send an Epson printer a file at 360 ppi and tell it to print at 1440 dpi, and the printer/driver will use (at least) four ink dots to make each pixel.

Truth in advertising is an interesting topic with scanner makers. Basically, they either out right lie or really bend and stretch the truth when talking about the resolving power of their scanners. It comes down to the conflicting ideas of how big the steps are that the scanner makes vs. actual optical resolution. Just because you can make 12800 steps per inch doesn't mean you can optically resolve 12800 spi (or anything even close to it).

Finally, there's the questions of what's actually on the film. What can a given film actually resolve, and when do you get scanner resolutions so high that all you are doing is looking at the spaces between the grain clumps / dye clouds? This in turn implies the question: What's the difference between more data and more information?

My short answer to your question of "How much dpi is enough?" is that it's somewhere less than 5000 spi, and that only for a very sharp and small grained film like, say, Velvia. A sharp large grained film like, say, Tri-X will be closer to around, say, 3800 spi or less even. This only if you used excellent glass, aren't diffraction limited, good solid tripod, cable release, etc....

That said, grain clump / dye cloud size is stochastic with a large standard deviation and is dependent on density and processing. The "optimum" scanning resolution for a given piece of film is therefore highly subjective. No one can give you a firm answer. What I've given you is just my highly generalized opinion after lots of experimentation and years of study. But that's all it is -- an opinion.

[Gordon Moat]

2400 or 2540 . . . though the importance might be something of more value in copydot scanning than film scanning. Regardless, this is a realistic target for large format film. If you are investigating drum scanners, either double or triple that value could still be useful.

Many scanners run into a maximum file size issue, either from buffers, software, or operating system limitations. There is also a practical matter of time required to scan at very high sample rates, because most scanners take substantially longer to scan at greater resolution settings.

There are workflows termed SOOM (scan once, output many), and there are advocates of scanning exactly at the values needed for a particular output. These are somewhat scanner or time related choices.

Last is cost: can you afford very large scans, or a very high end scanner, and do you have the luxury of time to scan and work with very large file sizes? Whether you pay for the scanner, or are buying scanning services from someone else, expenses can have a tendency to add up quickly. There is also a false economy of trying to work with low to mid range scanners; while low in initial cost, they can cost you in the long run either in time, or in a lack of the quality you might expect (based upon theoretical specifications).

Ciao!

Gordon Moat Photography

[Lenny Eiger]

How much dpi is enough.Some scanners go as high as 12,800 some 6400 and less, but what is a good average dpi both in scanners and in printers.

The 12,000 number is usually from a Tango. This is an excellent drum scanner that has an optical resolution that tops out at 4,000. There are two scanners that do an optical resolution of 8,000. However, does that mean it is no use to go past 4,000? Not exactly - there are some other factors in there. What it does mean is that there is a certain amount of sharpness the scanner is capable of... and the number of pixels are really more about what size you want to print it.

The printing (or "enough") numbers are simple. If you have a total of 4,000 pixels along your longest edge, and you want to make a 20 inch print, then divid the 4,000 by 20 and you get 200 dpi. If you want 360 for a 20 inch print, that's 7,200 total pixels.

The 6400 number looks like a number from an Epson flatbed. This is a different animal, not to be compared with a drum scanner. There are some who say the optical rez is about 2,000 or so. I think it is less than 1,000. In comparison to a drum scanner, they are very blurry. If you are an amateur and want to play around, why not. But not for professional use, in my opinion. High end equipment is expensive, no matter what it is... it's unfortunate. Most photographers are tinkerers, and make amazing things happen will all kinds of fun toys. However, it is impossible to make a Planar 80 out of toothpicks, and its kind of the same with scanners.

Lenny
EigerStudios