Slide, Negative Film, Photo Scanning: FREE Scanning Tips, Tricks, and Secrets

Resolution is tricky, it’s complicated, it makes no sense.  I’ll clear that up for you here.

Long, long time ago, when you use to go get your photos developed at a print shop nobody ever talked about resolution.  But, have you heard of DPI / dpi / dots per inch?  That’s where DPI came from– you get your photos developed and they came out 4″x6″ with a DPI of 300.

Are you asking the same question I am? Probably.  Why 300-DPI, why not 1200? Here’s why:

The image above is 4″x6″, 300-dpi scan of a negative.  Below, well, I scanned it at 4″x6″, but instead of 300, it’s 2400.  Here’s a 500×500 crop section of the scan (the actual size can fit a billboard):

If you look closely at the original, this is a close up of the cuation sign.  Anyway, so I increased the dpi to 1200 and do you see that it picked up any detail? No.  Did it make the image look any crisper? Sharper?  No.

The reason print shops stop at 300-dpi is because after 300-dpi you start picking up surface debris, dust, scratches, finger print stains… you’re no longer picking up any more detail of the image anymore.

So instead of worrying about DPI or PPI (pixels per inch), focus on the OUTPUT size.  Keep the DPI at 300, you’ll be safe there.  If you want a larger image, than change the output size, i.e. 4″x6″ or 8″x12″ or whatever you want.

You’re probably thinking, “But who cares.  I’ll never re-print these.  That’s the whole point of scanning them.  Why worry about what a print shop does?”  Ah, but what if you want to display your scans on your 52″, 1080p Plasma?  This is where understanding all this comes in.  Here, let’s find out what resolution you need to scan at to display your photos at hi-res.  Let’s take your HDTV, here’s its dimensions:

Your HDTV (no matter if it’s 32″ or 52″, plasma, whatever) is 1080 x 1980 pixels (that’s where they get the 1080 from).  Now, lets look at the dimensions of your 4″x6″, 300-dpi photo:

What’s the dimensions of your 4×6 scan?  How do you get that?  I just know you’re asking these important questions.
Well, we know your photo is 4″ x 6″ at 300 dot per inch.  Now, with some magic* how you get the height and width dimension is pretty simple:

Multiply 4″ by 300 to get height: 4 x 300 = 1200 pixels
Multiply 6″ by 300 to get the width:  6 x 300 = 1800 pixels

And, bang… 1200 x 1800 is your photo’s dimension.  Now compare that with your HDTV:

See that? Your 4×6 scan is equal if not larger than your HDTV.  That’s how you can get a small 4″x6″ photo scan look really good on a HDTV.  I know, my brain can’t wrap around it either– that a 4×6 photo scan can have the same resolution as a 52″ HDTV.  But it does.

So, what do you learn?

• That DPI isn’t that important when it comes to quality, it only makes the image larger.
• You don’t need a lot of DPI.  What you need is to make sure your output size is 4″x6″, or higher.
• That a simple 4″x6″ scan at 300-dpi is equal to HDTV quality.

Oh, something else to consider.  Have you ever wondered what the DPI is on a billboard?  Well, it’s 72-dpi.  But! the output size is 12 feet x 24 feet.  It’s the output size that counts.

Great.  Hope that clears some stuff up with resolution.

K.

*math