DPI to PPI conversion

Discussion in 'Digital Darkroom' started by western_isles, Sep 21, 2010.

  1. I need to find out if a Coolscan LS400 which works at 4000 DPI can create a digital file of 4000 PPI. The aim is to create a file of about 70mb from 35mm trannies.
    Without going into the technical side which I would be lost in, can anyone tell me if this scanner can achieve the output above?
    I have to chance to buy a used Coolscan for a good price as I cannot afford a new one costing about £2500
  2. DPI and PPi will be the same. If you scan at 4000 when you open it in PS it will be in DPI. You should easily be able to get your 70 Mb file from 35mm slides.
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  3. If you scan at 4000 when you open it in PS it will be in DPI.​
    Photoshop uses PPI, not DPI
  4. Do you really need 70mb files?
    Anyways, there is no conversion. DPI is dots per inch. PPI is pixels per inch. Print your 4000 PPI file to 4000 DPI and you've changed nothing. Scan your 4000 DPI print in as 4000 PPI and you've changed nothing. All you're doing is changing weather it's displayed or printed. It's still 4000 per inch. There are much better things to get bent out of shape over than wether it's DPI or PPI.
  5. Scanners and camera make pixels so PPI. Output devices (displays, printers) make dots so DPI.
    There doesn’t have to be a 1:1 relationship between the two but that is often the case. For example, an Epson may output 720/1440/2880 dpi. You would NEVER scan an image at anything close to even that lower value.
  6. Frank,
    DPI and PPI are often used interchangeably in the common vernacular. Strictly speaking, a "pixel" is the smallest element of a digital image which contains information about all three (four) colors and their intensity. In your case, DPI and PPI mean the same thing, because that is how Nikon and Adobe use the terms.
    A "dot" is somewhat ambiguous. In addition to the above, "dot" refers to the smallest element of a printing process. In half-tone printing, "dots" are defined by the screen frequency. Each color has a "dot" and each "dot" varies in size to emulate a change in density. If the screen is sufficiently fine, your eye interprets the result as a continuous tone.
    Inkjet printing uses yet another common definition of the term "dot". In this case, a "dot" is literally a dot of ink which is either there or not there. In order to emulate a continuous range of tones, these dots are grouped in 8x8 dot arrays, containing from 0 to 64 dots of ink. Each array can therefore display 64 different tones, and each ink has its own dot array. (The dots are dithered in a proprietary fashion so that the underlying grid is disguised. Epson also has up to 4 different dot sizes, increasing the number of intermediate tones). In short, it takes a square 8 dots on a side to describe one pixel. Consequently a 1440 DPI inkjet printer is the equivalent of 180 PPI (1440/8).
  7. I have to apologize about my early comment, I didn't intend it to come across as crass or flippant. Some people get very upset if you substitute DPI for PPI, while others recognize that it's simply a label (dots vs. pixels). Here's more to the point of what you're asking. You can scan with that printer at 4000 PPI. You can then print that scan at 300 DPI, many times you can print to a lower DPI and get away with it, but 300 DPI seams to be the standard most people aim for.
    Most other scanners, even the ones that claim astronomical PPI's, won't out perform your Nikon Coolscan scanner. Some will, many wont, some will cost even more. A drum scanner would be many times the cost you're talking about.
    You should rephrase the question to ask wether this is a good scanner and if not which would you recommend.
  8. In scanners "DPI" has been used for over 1/3 century.
    This bother the living dickens out of newcomers to digital; ie folks with no long term experience.
    About every scanner ever made uses the dpi jargon,
    Our 35mm slide scanner from 1989 used dpi then; and folks were not confused or on a warpath then that "dpi is wrong"
    ****The oddball thing is dpi with scanners is older than photo.net; older than Photoshop.
    Dpi is used in formal bids in scanning for government stuff even 20 years ago. Dpi is in legal US Patents with flatbed scanners and Fax machines and goes back to the DOS era with scan wands that scanned a 200 to 300 dpi.
    Some Folks NEW to digital have a burr up their bum and like to say dpi is wrong with scanners; they are just ignorant of 1/3 a century of actual industry usage. Like any newcomer to an industry; making up new terms is for ego reasons. ie film is no longer film it is "analog".
    For those of us who have used scanners for 25 years with dpi; the anti scanner dpi agenda seems childish; I wonder what other holes folks have in their education.
    What has happened is some digital book writers with little long term experience have gotten into this "dpi is wrong with scanners" soapbox; thus now in the last 5 years there are folks who pop into threads if one mentions one scanner a 6x7cm negative ona Nikon 9000 at 4000 dpi. They parachute in to try to correct. Maybe the same folks will discover a 2x4 is not really 2x4 inches too; to appear smart? maybe they can come up with new terms for floppies; jazz or zip drives?
    On photo.net there is a newbie flippant jump into decent threads about scanning only to preach their silly "dpi is wrong with scanners dogma" .
    To somebody who has used scanners for 1/3 century with dpi setting; these folks come across as jackasses. Here I have many dozens of scanners; over 100,000 bucks worth of them. A 2009 14 grand RBG color scanner that is 36" wide is in dpi ; the 1989 35mm slide scanner is in dpi. There has been only one scanner we had that had pixels per inch in its software; and that was an engineering scanner back in the DOS era that used a 386 computer.
    99.999 percent of the scanners ever made in the last 1/3 century use dpi. Now that scanning has peaked and is fully mature and in a decline; some folks are on the anti dpi soapbox to make them look like a dunce; ie ignorant of about every scanner every made.
    Scanning is so mature that Minolta; Canon dropped out; Nikon has just one model.
    If Acme brings out a scanner in 2011 with ppi marketing; they face public confusion since about all other competitors use the 1/3 century plus industry standard lingo. It is like if Acme makes mowers; it is better to say the blade is 32 inches than 32 centons.
    The sad thing is if one scanned a 35mm slide 20 years ago at 2000 dpi one understood it was 2000 pixels per inch in an image program. Today somehow his trival matter bugs the crap out of many folks.
    Really none of this "dpi is wrong with scanners" was around 10 years ago; ie totally unheard of. And that is when scanner sales peaked.
    The publics confusion of this simple stuff is so bad that an editor friend of mine uses me to buffer the public's digital image inputs. An editor can ask for a 5x7 inch image at either 300 dpi or ppi and they really want at least a 1500 by 2100 pixel image. The math is not that hard; say 1 home school house 2nd to 3rd grade 200 years ago. Since the same editor used me back in 1989 for scanning 35mm; there is now way in hell are they going to jump on the "scanners are in ppi soapbox" . If the editor's assistant says the slides need to be scanned at 4000 ppi; I still use the 4000 dpi setting in the scanners software.
    What matters is clear communication.
    Trying to change all scanners to be now in ppi is silly.
    If there is a nice civil thread about a 4800 dpi Acme 4800 flatbeds performance; I might say mine is really like a 1800 dpi film scanner; or I might say it really is just 1800 ppi too. *IF* one uses the dpi term; flippant folks in the bleachers jump in to "correct you" they add zero technical information. It is like they are a bunch of old biddies in grade school who correct english; and have this high horse I am correct you are wrong flippant attitude. One can go back to a graphics book of the early 1980's for DOS and one has Dots=Pixels defined
  9. In scanners "DPI" has been used for over 1/3 century.​
    As Andrew correctly stated, scanners create pixels, not dots. Just because a term is widely used doesn't mean it's correct. At this more informed point in history we understand the clear difference that exists between the pixels in a digital image and the dots that a printer puts down. The distinction is useful and important, and the separate terms exist for good reason.
  10. Kelly, Ipresume that by " folks with no long term experience" you are referring to digital experience? I started photography in 1961 with my fathers old Contax which I think qualifies me as having "long term experience" in photography.
    Dan has hit the nail on the head, my question should have been "is this a good scanner and if not which would you recommend".
    My options are:
    1. Second hand Nikon Coolscan LS4000 at £599 or
    2. New Plustek 7600i Ai OpticFilm Scanner at £369
    Money is an issue, I would like a multi format Nikon at £2500 odd but my wife and cat would divorce me if I even contemplated buying one.
    I like Nikon kit as I use their cameras in addition to Mamiya and have not heard of Plustek before.
    Anyone out there with experience of these two scanners? Feed back would be appreciated.
  11. Just because a term is widely used doesn't mean it's correct.​
    Agreed. We need to remind Kelly about an old Chinese proverb: The first step towards genius is calling things by their proper name.
    Scanners are a dead market, that’s why so many have left the market. Its all about digital capture. Its why we see so few carriages built these day for horses! The Amish might buy em, but few others and its pretty obvious in this market or even a robust one why they are not built.
  12. Actually the first step towards genius may be to be able to follow a coherent conversation.
    Frank, I've used neither scanner and nobody is chiming in with anything that's useful. So you're probably going to have to check the reviews.
    I've read here and other forums that most scanners won't resolve much past 3200 PPI. So that levels that playing field of the 4000 PPI vs 7600 PPI scanners to about equal. Both have a type of dust removal, but I've read that Nikon scanners do the infrared "exposure" at the same time as the main exposure and most other scanners don't. I know my HP scanner has to take a second pass doubling the time to scan. I read in one review on the Plustek that it takes longer for dust removal scans but found no mention on the Nikon scanner.
    Another thing you'll have to consider is that with Nikon either not making scanners anymore or only making them in batches you may find getting parts to it are harder to come by.
    Also find out the D-max of the specified scanners.
    Does one scanner use glass and the other doesn't? Glass collects dust.
    What are the scan times?
    What software comes with the scanner? The Nikon scanners software may not be transferrable.
    I know I've said a few things that look better for the Plustek, but I've seen too many conversations here and elsewhere claiming that Nikon knows what it's doing to just give it the brush off. Hopefully someone here can actually share their experiences with one or both.
  13. The coolscans are some of the best home scanners available. I have not used the plustek but my assumption would be that their dpi claims are way over inflated marketing statements and not backed by any real examples.
    Are you sure about the model number? It sounds like a really old one and I can't say what the specs are for it. or if you will have issues finding drivers or a working scanner. The latter coolscans do scan at a real 4000 dpi/ppi.
    However, film dpi/ppi scans do not equate to DSLR ppi. IMO you will need a lot more pixels from film to print large or for heavy cropping, than you will from a digital capture. If you stated your goals of your project someone with similar goals could give you some insight. Like print sizes, or you plan to work in film rather than DSLR or that you have a film library you want to digitize.
    In all, my advice would be to use a film scanning service like scancafe.com if you have to scan film. Scanning is not easy, and takes a lot of time. Time better spent elsewhere for most people.

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