35mm film is estimated to have about 20 megapixels worth of visual data¹ which requires scanning it at around 4,000DPI. However, your goals for the image and the tools you have available will determine the best scanning resolution for your project.
This guide will lay your options out in detail so that you can make the best possible decision for your film scans. I will go over three scanning scenarios, each with distinct requirements: the Web, print, and archiving.
DPI isn’t the only value you’ll need to consider when scanning nor is it as straightforward as some may think. Here you will find a full explanation for what it really means, as well as other important attributes like DMax and bit-depth.
✪ Note: To get acquainted with the terms used in this article, have a look at the glossary below.
If you’re looking for quick answers: read the first paragraph of either Web, print, or archiving sections.
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The best scan resolution for the Web.
35mm film will work best on the web when scanned at 2,700DPI and saved as a JPEG file with compression set to 80. Medium format will produce a similar file when scanned at just 1,200DPI. 4x5 only needs 650DPI, and 8x10 will do fine at 320DPI.
This website features some of the highest-resolution images on the web at 1,800 pixels wide. Instagram downsizes everything to 1080 pixels wide. Other sites like Twitter, Flickr, or photographer portfolio websites may allow higher-res scans; however, that isn’t always a practical resolution for the Web.
Web browsers can resize huge images to fit on the screen, but the weight of the image file will affect their performance. In my experience as a web designer, developer, and active sharer of images online, photos that are 2,500 pixels wide tend to work best for most web or app uploads. Many websites and apps have a cutoff at 5MB for image uploads making that a good target maximum.
Your image’s height, compression, and tones can dramatically affect the file weight. I found that 2,500-pixel-wide images saved as JPEGs with the quality at 80 usually fit well within the 5MB.
Assuming that 2,500-pixel dimension is the minimum for the sake of vertical image scans, we are looking at 2,500 / 0.94” ≅ 2,700DPI for 35mm film (where .94” is the frame height, converted from 24mm). Using the same formula of 2,500 / frame height in inches, we get ≅ 1,200DPI for medium format, ≅ 650DPI for 4x5 large format and ≅ 320DPI for 8x10.
If you’re scanning 110 film and looking for the same 2,500 pixels on the short side, you’ll need to scan it at nearly 5,000DPI.
✪ Note: Keep in mind the differences between the interpolated and optical scanner resolutions. Consider saving your scans as TIFFs or other non-lossy formats at 16-bit per pixel (if you have that option) in addition to your JPEGs — this may help you get better results if you plan to edit your scans or invert the negatives by yourself.
The best scan resolution for making prints.
35mm film should be scanned at 2,700DPI for 8x10” prints and saved as a TIFF file. Medium format will produce a similar file when scanned at just 1,200DPI. 4x5 only needs 650DPI, and 8x10 will do fine at 320DPI.
There’s barely any limit to what you can do with print, so I’ll focus on 8x10”, which fits perfectly on the standard A4/Letter paper. The scan file that works for 8x10” will do even better for smaller print sizes. Assuming that you’ll be printing at 300DPI — perhaps the most quoted recommended resolution for print.
Turns out that an 8x10” print at 300DPI will need 2,400 pixels on the short side, which is almost the same as the 2,500 recommended for the Web above. But instead of a JPEG, I suggest you save your images as TIFFs for optimal print quality.
✪ Note: If you’re planning to crop your images, you may want to scan at a higher resolution. Larger prints at the same pixel density are easy to extrapolate from the above figures.
The best scan resolution for archiving film negatives.
If you plan to archive your film digitally, scan it at a max optical resolution and save it in uncompressed TIFF or RAW files. Consider other constraints, such as storage space and your time. Limit large format scans to 2GB for practicality and device compatibility.
You may want to scan once to keep a future-proof digital copy of your film. For this, you will obviously want the highest resolution possible so that your file may be good for the enormous prints and ultra-high-resolution displays of the future. However, you will still be limited by the amount of storage space you have available and some false promises written on the box of your scanner.
A single 16-bit TIFF file scanned at 5,000DPI from 35mm film can take up two to three hundred megabytes of disk space. On my machine, I have nearly 6,000 scans which weigh close to 1.5 terabytes.
If you are prepared to invest in digital storage, top resolution scans are what you want. But make sure that you figure out your scanner’s optical resolution and use that as the max to avoid wasting your space on interpolated pixels.
4,000DPI, according to one estimation, is the maximum visual resolution an ISO100 film may carry. This, of course, does not take into account slower speed films and the value of grain detail. However, you will need to consider the trade-offs when scanning large format film at 4K+ DPI, which can easily swell to over 1,280MP (≅ 3.5GB+) with an 8x10.
Mind that your scanner resolution and bit-depth aren’t the only factors in the scan quality. A higher DMax resolution will do a better reading of highlights on your negatives; the software and the scanner hardware may also play a role.
You may also want to consider making backups and/or paying for cloud storage service as a failsafe for failed hard drives and general data loss.
Bit depth (image) — a number of bits of colour assigned to a single pixel. All JPEG images are 8-bit per channel (red, green, blue) or 24-bit in total. TIFF and RAW images can have 16-bit per channel or 48-bit+ in total. A higher bitrate will provide greater flexibility when editing images and a larger file size. The total number of colours in 1-bit is 2 (2¹), 2-bit is 4 (2²), 4-bit is 16 (2⁴), 8-bit is 256 (2⁸), 24 bit is 16,777,216 (2²⁴), etc.
DMax — a maximum density of silver halide crystals that the scanner can distinguish. Higher DMax scanner capability will let you preserve more detail in your negatives’ highlights.
DPI, dots per inch — a number of pixels assigned for a single inch of an output of an image. 1MP image can be printed at 3⅓ ✕ 3⅓ inches at 300DPI. Note that the same 1MP image can be printed at 10 ✕ 10 inches at 100DPI.
JPEG — the most popular image encoding format, particularly on the Web. All JPEG images are 8-bit per channel (red, green, blue). They are compressed with some data loss.
MP, megapixel — one million pixels. An image measuring 1,000 by 1,000 pixels is 1,000 ✕ 1,000 = 1,000,000 (1MP).
PPI, points per inch — this is a print resolution. A printer may print an image set at 300DPI at a resolution of 1,200PPI — in which case 4 dots of printer ink will make up a single pixel.
Scanner interpolated resolution — total pixels/dots per inch (DPI) the scanner can generate from a single inch of film after computationally increasing that number using an algorithm. For example, when you resize your 1,000 ✕ 1,000 pixel image to 2,000 ✕ 2,000 in Photoshop, you are interpolating a 1MP image into a 4MP image, but you are not adding any real-world data.
Scanner optical resolution — total pixels/dots per inch (DPI) the scanner can generate from a single inch of film.
TIFF — is a popular format for lossless image storage with applications in print, image manipulation, and archiving. TIFF images may be compressed (without data loss), and they may be 16-bit per channel.
1. Langford, Michael (2000). Basic Photography (7th Ed.). Focal Press.