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cglenn7777
cglenn7777
Known Participant
July 3, 2018
Question

Confused about DPI and image size and depth

  • July 3, 2018
  • 1 reply
  • 4460 views

I have been scanning my college days (circa 1972-1980) 35mm color slides into the computer.  In the (Epson V550) software, I set the depth to 24bit and the DPI to 4800, in case I want to blow any printed up to poster size, and I set the image dimensions to 1.28 x .86 (which is the actual measure of the photo portion of the slide.

After editing and saving an image in Camera Raw, I open the images in my preferred viewer (Lyn for Mac), and it lists the DPI of the PE edited image as 300.  The image resolution remains the same (4060 x 6113 pixels).  But when I view the numbers inside of PE, it lists the resolution of my edited and 'saved as...' file at 4800 DPI and the size is very close to the original: 1.274 x .846.  Also, I see in Finder the file has greatly increased in size (3.9 to 6.6 meg).

Clearly confused here!  And then there is the depth.  I don't fully understand it, but from my audio experience, I thought depth dealt with quality, so that 24bit had more information and thus larger file size, but here, dropping from 24 to 16 added over 2 meg to the file size.

Most important to me is the DPI, and I have no idea why it would read 4800 inside of the PE image>adjust size but only 300 in a photo viewer.  I don't know why PE does not support 24 bit.  And I don't understand why reducing the DPI and bit would result in a significant increase in file size.

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      1 reply

      hatstead
      hatstead
      Inspiring
      July 4, 2018

      Some thoughts:

      1. DPI = dots per inch. This is determined by your printer.
      2. PPI = pixels/inch. This is the resolution of the file, and can be altered by re-sampling.
      3. The expectation that one can enlarge the tiny bit of information inside the 35mm. slide to poster size is unrealistic.

               What are you really trying to do? Where is the problem?

          4  Have you tried scanning these old slides with a dedicated scanner, e.g. Wolverine 35mm Film to Digital

          Converter?

      cglenn7777
      cglenn7777Author
      Known Participant
      July 4, 2018

      Hi again!  When I was searching for scanners for this project, I did not know of the Wolverine or anything specifically dedicated to such purposes.  I did not know to not limit my search to flatbed scanners.

      I'm doing two things, One is to be able to view my slides on a large TV.  While I currently have a 65" TV, in the not too distant future, I expect to have a much larger one for a dedicated home entertainment center.  Second, I may want to print a few of my best into a size larger than 8x10, with the size perhaps being limited by the image quality.

      I'm entirely self taught, and what I read said to make the scan size the same as the original, and the more DPI the better (which is what Epson labels it...there is no PPI setting I can find).  I chose 4800 as a compromise.  It takes 1:30 to scan one slide in at this resolution.

      hatstead
      hatstead
      Inspiring
      July 4, 2018

      I have digitized about 200 35mm.slides using the Wolverine converter with excellent results. There are other machines for this purpose as well - check on Amazon. One inserts a camera card into the machine, and uploads to the computer via this medium. The resolution of the digitized file is 72px/in. Generally speaking, it is desirable to have resolution in 240-300 px/in range for printing, but I have printed at lesser value without undue pixellation.

      As for display on your TV, I have no experience with this, but you can try it with one of your files.

      There are also commercial labs that digitize, e.g. https://dpsdave.com/slide-scanning-prices/

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