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Scanning 35mm colour negatives .. what dpi?

Discussion in 'Digital Image Editing & Printing' started by Rupert49, Jan 25, 2013.

  1. Rupert49

    Rupert49 Well-Known Member

    I hardly ever scan colour negatives, but today I needed to do so because some original prints from 1982 had gone missing.

    I initially chose a resolution of 300dpi, thinking that would be more than adequate (it usually is when I scan prints) but this only rendered a 100% image size of roughly 11x7cm (approximately 415x258 pixels) which looked awful as a 6x4" print.

    So I repeated the process, this time at 720dpi, which this time rendered a 100% image size of roughly 26x16cm (approximately 995x625 pixels) which was adequate for the purpose of replacing the lost originals, but wouldn't have stood any enlargment much above, say, 8x10".

    I appreciate that you can't add detail to an image that wasn't there in the first place but, as a matter of interest, when scanning 35mm colour negatives, what would you say was the optimum scan resolution to use to get a decent quality print that could stand enlargement if required?
     
  2. AlexMonro

    AlexMonro Old Grand Part Deux

    A 35mm frame is roughly 1x1.5". So if you want to print to 8x10" at 300 PPI, you're going to need 8x300 = 2400 pixels from that 1" height of the negative.

    So minimum scan resolution of 2400PPI. You may want to experiment a bit to find what scan resolution works best with the grain size of the film you're scanning.
     
  3. Roger_Provins

    Roger_Provins Well-Known Member

    Rightly or wrongly I've always used 4000 ppi with a dedicated Canon slide/negative scanner. Slow but results seem fine to me.
     
  4. thornrider

    thornrider In the Stop Bath

    It depends on your scanner and the software you are using - the max on my Nikon Coolscan IV with Silverfast 8 SE Plus is 2900 DPI and that gives me a 36Mb TIFF file - 4046 pixels x 2546 pixels. Equates to a 12.5 in x 8.4 in print.
     
  5. taxor

    taxor Well-Known Member

    I also scan at 4000 ppi. Low(er) res scans can have that pixelisation that makes some digital retouching methods difficult
     
  6. Benchista

    Benchista Which Tyler

    I scan at the highest optical resolution of the scanner unless I know I can do with less.
     
  7. P_Stoddart

    P_Stoddart Well-Known Member

    Yes, you should scan at the limit of the scanner in question for archive purpose.

    But I found most colour neg really does not need more than around 6MP anyway.

    You are bound to see the structure of the film at 6 or 8MP.

    Now for a 8x10 photo prints at 300ppi you need at least 7.2MP for 8x12 then 8.6MP.

    For a standard 6x4 print it is only 2MP or 1800x1200 pixels. Hence your 6x4 from your scan looking very poor.
     
  8. Benchista

    Benchista Which Tyler

    Sorry, but that's simply wrong; what you see is "grain" (or dye clump) aliasing, the effect of which reduces as you increase the sampling resolution.
     
  9. thornrider

    thornrider In the Stop Bath

    Nick is right - the old software which came with negative scanners hid the capability of the scanner - especially Nikon's own software which came with the Coolscan IV. When I shifted to an iMac the software was not supported on OSX except in early versions - so to cut a long story short - I found Silverfast in Germany and immediatey had multi-pass scanning on the Coolscan - grain disappeared. Since then the software has been upgraded to Silverfast 8 SE Plus with 16 bit scans and the performance has increased to levels I would not have believed possible. The Coolscan IV is limited to 2900 DPI - pity I can't find the 4000 DPI MkV but they are selling secondhand for more than when new. So how old is your scanner software ?

    By scanning at the max and then squeezing down the print size to A4 the results are stunning even on ASA 400 colour negative film - on slides like Kodachrome 25 it is unbelievable. Go for the max.
     
  10. Rupert49

    Rupert49 Well-Known Member

    Thanks to everyone for their input to this thread.

    As it happens, my Epson V500 has an upper scanning resolution capability of 12800dpi (16-bit) which, for just one 35mm colour negative, takes about 15 minutes to scan!

    Out of interest I tried re-scanning one of the negs I'd previously scanned at 720dpi, but this time at 9600dpi. The results were interesting, as follows:

    At 720dpi the jpeg produced measures 993x624 pixels, with a file size of 110KB
    At 9600dpi the jpeg measures 13248x8384 pixels, with a file size of 5.41MB

    .... quite a difference!
     
  11. P_Stoddart

    P_Stoddart Well-Known Member

    I doubt very much the images are on high performance colour neg. Therefore at around 8MP

    you are going to see the film noise. Basically what makes up the image.

    Roger Clark covered this quite well:

    http://www.clarkvision.com/articles/film.vs.digital.summary1/index.html

    Most colour neg shots are either 100ISO or 200ISO.


    Finally 8MP or a bit more is good enough for A3 prints with borders with alittle interplolation. :)
     
  12. thornrider

    thornrider In the Stop Bath

    I think "good enough" means you can't see the pixels in an A3 print - that doesn't mean you have resolved all the detail in the negative. It's the scanner that has noise if the software is primitive - not the negative.

    Finally, 100 ASA and 200 ASA are some film speeds - 400 ASA is now as fine grained so it makes a good general purpose film.
     
  13. Meredith

    Meredith Well-Known Member

    The maximum optical resolution of the V500 is 6400dpi so no need to scan at a higher resolution. Higher resolutions are interpolated. It most likely cannot resolve more detail at a resolution somewhere below 6400 as well so if you work out where that level is then you don't need to scan at a higher res than that level.
     
  14. LargeFormat

    LargeFormat Well-Known Member

    The best resolution that film can offer is about 4,000 dpi so at that resolution you will be resolving everything recorded on the film. It is about equivalent to 24MP.
     
  15. thornrider

    thornrider In the Stop Bath

    But that would be a JPEG - surely a TIFF would be better because of post scanning manipulation ?

    Ref : I get a 36Mb file at 14bit from a 2900 dpi scan
     
  16. LargeFormat

    LargeFormat Well-Known Member

    Sorry I don't understand this. The scanning resolution has nothing to do with whether it is subsequently saved as a TIFF or a JPEG or anything else. I agree that a TIFF is better than JPEG if any post capture manipulation is to be carried out although the same could be said for, say PNG or any other non-lossy method.
     
  17. thornrider

    thornrider In the Stop Bath


    Not what I meant. A JPEG is much smaller than a TIFF - so to get a smaller file than I get with you using 4000 dpi and me using 2900 dpi you have to be using a JPEG. Does this mean that you print straight from your scans - because each time you modify a JPEG your file will deteriorate.
     
  18. LargeFormat

    LargeFormat Well-Known Member

    No, no, no!!!!! that's not what I'm talking about.

    I said 4,000 dpi which roughly on a 1" by 1.5" piece of film gives a file that is 6,000 by 4,000 which is 24MP (megapixel no megabyte). My scanner at 4,000 dpi gives much the same file size in both megabytes for TIFF and in megapixels as does my FF 24MP camera.
     
  19. Roger_Provins

    Roger_Provins Well-Known Member

    Exactly the same here - about 24MP files from Sony a900 or 35mm film scanned with Canon FS 4000 US.
     

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