Best resolution when scanning 35mm slides

Best Resolution When Scanning Slides Into Digital

A Simple Way To Understand Slide Scan Resolution

I'm going to show you a simple way to look at resolution. Once you understand this, the rest will be easy. You'll know exactly what DPI you'll need. No matter what size slide you're scanning. Or how big you want the digital image to be. Read this article, and you'll know resolution like a pro...

Is 4000 DPI The Best Resolution To Scan Your Slides?

Here is the quick answer: if you are scanning a 35mm slide, set your scanner resolution to 4000 DPI. This will give you a 18 mega pixel scan. It will have a dimension of 5300 x 3500. And it'll be a 18" x 12" high-resolution digital photo.

You can also set your DPI to 300 DPI, and set the OUT PUT size to 17" x 11". And you'll get an 18 mega pixel scan. And it'll have a dimension of around 5300 x 3500.

But Wait! Let's Geek Out More So You Finally Understand Resolution

If you want to go deeper and find out what all these numbers mean, I have put together a guide to help you understand. I tried to put it as simple as I could, and once you grasp this, you will have more control over your slide scanning project.

How Understanding Resolution Can Help You Get Better Slide Scans

Say it is your Dad's birthday and you want to print a poster from one of his slides. When you walk into the print shop with your 4000 DPI scan, they might tell you to come back with at 300 DPI image.

So you re-scan your slide at 300 DPI. You go back to the print shop with their suggested 300 DPI digital image. Your poster is made, and the image looks stretched, there is no detail, it just looks bad.

What is going on? Well, resolution is confusing because there is a lot of numbers that are thrown around. You have dots per inch, pixels per inch, resolution, pixel dimension, mega pixels-- which all mean the same thing really.

Follow me and I will guide you in a non-technical way to understand what resolution is. Once you learn these things about resolution, the rest will be easy and your family will be impressed you know so much about digital imaging.

1. What Happens To Your 35mm Slide When It Is Scanned At 4000 DPI

Take a look at your 35mm slide. Most slides have a dimension of around 1.30" x 1.85". Have a look...

The actual size of a 35mm slide is about 1.35 x 0.80

So when you tell your scanner to scan at 4000 DPI, what it does is it squeezes 4000 pixels for every inch. By squeezing, I mean it multiplies the height and width of your little 35mm slide by 4000 DPI. Let me show you...

What happens to a  35mm slide when scanned at 4000 dpi

And what you end up with is what is called the Pixel Dimension. The dimension of your digital image is 5200 x 3400. And how you get that is, 1.3 multiplied by 4000 = 5200; 0.85 multiplied by 4000 = 3400. Have a look...

A 35mm slide scanned at 4000 DPI will give you a 5300 x 3500 digital scan

2. You Have A 5200 x 3400 Digital Image, Now What?

The best way to understand what Pixel Dimension is to look at your 1080p, HDTV. Your HDTV has a pixel resolution of 1920 x 1080. It does not matter if it is 32" or 52", it still has a pixel dimension of 1920x1080...

A 1080p HDTV has a dimension of 1080 x 1920

Now, compare your 35mm slide scan with your HDTV...

A 1080p HDTV has a dimension of 1080 x 1920... your slide scans are 5200 x 3400

(Aug. 2015 Update: A 4k HDTV has a dimension of around 3800 x 2700)

Your HDTV is 1920x1080, where your 4000 DPI slide scan is 5200x3400. Your digital image is well above HD quality. So why would you want it that large? Simple... it is better to have too many pixels than too little.

What I do is scan my slides at 4000 DPI and keep those archived, and never touch them. Then I make copies, and size down the the copies for whatever use I need them for.

3. What Does 5200 x 3400 Mean In Inches?

Your 4000 DPI / 5200 x 3400 digital image works out to be about an 18" x 12" photo. How you get this is pretty simple math. And if you get this part coming up, then you will know how to re-size your scans for your end use.

Maybe like me, you grew up using inches when it came to physical photos. You have your standard 4"x6" or 8"x10" photos. How does a Resolution of 4000 DPI and Pixel Dimension of 5200 x 3400 work in inches?

Grab an actual 4"x6" photo. Have a close look. If you look at the actual print surface you may notice that the photo was printed using coloured dots.

When you had your photos developed, what the photo lab did was print 300 dots of colour for every inch. Sort of like this...

A 4x6 photo has 300 dots per inch

Photo labs use 300 DPI as a standard resolution. I am sure there are colour printers that can do more than 300 DPI, but most physical photos are developed at 300 DPI.

So, the photo lab basically does what your scanner does: squeezes 300 dots for every inch. Your photo then has a Pixel Dimension of 1200 x 1800. How? Here's what I mean...

A 4x6 photo scan at 300 dpi will be a 1200 x 1800 digital image...

  • 4" x 300 DPI = 1200
  • 6" x 300 DPI = 1800
A 4x6 photo has 300 dots per inch... or 1200 x 1800 pixels

So what about a 4000 DPI slide scan? OK, if you walk into a print shop with your 4000 DPI slide scan, they can print your digital image as big as 18" x 12". You will still get a 300 DPI physical photo, but it will around 18" x 12".

Let me show you what I mean...

A 4000 DPI slide, 1.35 x 0.85 scan is...

  • 1.35" x 4000 DPI = 5400
  • 0.85" x 4000 DPI = 3600

A 300 DPI, 18x17 photo print is...

  • 18" x 300 DPI = 5400
  • 12" x 300 DPI = 3600

You see, both are 5400 x 3600! This is called DIMENSION. It's the most important number to look at.

Forget about dpi, ppi, 18x12, resolution... always look at the DIMENSION. That is your litmus test on how big your digital image is.

4. What Is A Mega Pixel, And How Do You Get One

Have you ever wondered what "Mega Pixels" mean? Well, remember your Pixel Dimension, 5200 x 3400? Just multiply those and you get close to 18 million, or 18 mega pixels.

A 4000 DPI slide scan is 18 mega pixels

Digital cameras like to use mega pixels mostly for marketing. It's a lot easier to say 18 mega pixels than 5300 x 3500 pixel dimension.

5. Say You Scanned Your 35mm Slided At 3000 DPI

One more example...

What happens when you scan your slide at 3000 DPI? What sort of Pixel Dimension and Mega Pixels will you get?

Lets do the same thing. Take your 35mm slide, and lets multiply 3000 DPI for every inch...

A 35mm slide has a size of 1.35 x 0.85

And if you scan it at 3000 dpi, you get a 9 Mega Pixel scan. Here's what I mean...

A 35mm slide scan at 3000 dpi is 9 mega pixels

Again, here is how we got everything...

  • Pixel Dimension: multiply 3000 DPI by the height by width of the actual size of the slide
  • Photo Size: divide the Pixel Dimension by 300 (300 DPI being the resolution print shops use to print physical photos)
  • Mega Pixels: multiply the Pixel Dimension (height x width)

6. A Cheat Sheet Of Everything

Here is everything I talked about in a simple cheat sheet...

Best resolution when scanning 35mm slides

Free Ebook: Tells You Secrets To Getting High Quality Slide, Negative, Photos Scans In Half The Time

Which of these saning troubles do you want to overcome?

  • What's the best resolution / DPI to scan your slides, negatives, and photos -- so you don't lose details
  • Best method to digitize slides, negatives, photos using your regular flatbed or film scanner
  • How to clean your negatives, slides, and photos before you scan them -- so you don't scratch them
  • What side should you scan a slide or negative -- so they're not backwards or facing the wrong way
  • How to setup your scanner to get higher quality digital images -- 24bit JPEG? 48bit TIFF?
  • How to fix your digital images using Digital ICE, GIMP, or Photoshop and make them look new
  • How to improve your scan workflow so you can double your productivity and finish your project twice as fast
  • Understand the technical stuff of a digital image so you can make sideshow videos, reprints, and more!

Hey, my name is Konrad. I've been scanning professionally since 2005. I've helped multi-billion dollar companies, pro sports teams, pro photographers, artists, museums, book publishers, etc. I've scanned over 930,000 slides, negatives, photos.

The reason I'm telling you this is because no matter what challenge or frustration you're having, I know exactly what you're going through. So, to help you RIGHT NOW, I've put together a super simple scanning guide to get you started.

It's free (for now). So, fill out the form you see on the right:

How to scan slides negatives photos into digital, free ebook download

Your free ebook is up for grabs. Just enter your name and email, and click the download button: