Pixels Per Inch (PPI) Vs. Dots Per Inch (DPI)

March 9, 2017 -

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If you’re wondering how to resize your image to share on the interwebs then you may have come across different methods or guidelines that tell you it should be ”72 DPI” or “100 PPI” or “1920 pixels on the longest side and 300 DPI”.

 

What does any of that mean? Is it important? Can’t I just save my image and let Facebook sort it out for me?

 

Resizing your images before uploading them is important for 3 reasons:

  • It reduces file size, making uploading faster
  • It reduces file quality, making images less “stealable”
  • It compresses the image in size to avoid websites compromising on quality

 

But what part of the image should you focus on?

 

Let’s look at the terminology.

 

Pixels Per Inch (PPI): relates to digital files and the number of little coloured squares over a given distance, in this case, an Inch.

 

Dots Per Inch (DPI): relates to printing and has nothing to do with your computer screen. Multiple dots can make up a single pixel on paper and depends on the printer.

 

OK so now we are getting somewhere. We can ignore DPI completely when it comes to preparing files for the internet. But be aware that these two terms are used interchangeably when they shouldn’t.  We can save preparing images for print for another time. But just to drive home the point, here are 3 images saved at 300 DPI, 100 DPI and 5 DPI respectively. All are 2000×1000 pixels (2MP).

 

300 DPI @ 2000×1000

300 DPI

 

100 DPI @ 2000×1000

100 DPI

 

5 DPI @ 2000×1000

5 DPI

 

Can you see the difference? There is none because each image is still 2000×1000 pixels in dimension. And no I haven’t just put the same file in 3 times, although that would have saved us some time. If you don’t believe us you can try for yourself.

 

So how does PPI affect the image? If you are just simply making the image smaller by reducing the pixel size then you won’t need to worry about what the PPI is. The problem will arise when you want to increase the amount of pixels.

 

Here is an example of what would happen if I resized the image to 5 PPI (96×48 pixels) and then tried increasing the size back to 2000×1000 pixels.

 

5 PPI @ 2000×1000

5 PPI image upscaled to approx 100 PPI

 

Now you can count the pixels in an inch quite easily! Well…not really. Because, now that I’ve made it 2000×1000 pixels again the PPI is closer to 100. But that’s just a technicality so you can see what 5 PPI might look like if you could zoom in on your screen. Here is the real 5 PPI image:

 

5 PPI Small

 

What does the original file that was 5760×2880 look like? Here is a 2000×1000 crop from a section of it. This means it is the same PPI (resolution) as the first 3 images

 

Original Crop @ 2000×1000

2000×1000 (approx 100PPI) crop from the original 5760×2880 file.

 

And just for fun, can you pick the thumbnail of the 5 PPI image upsized to ~100 PPI from this line up?

Probably not considering all the thumbnail “resolutions” are the same, about 5 PPI.

 

So what can we take away from all this?

  • Only worry about pixel dimension when resizing your images for the internet.
  • Ignore DPI all together.
  • Only worry about PPI if it happens to be to exact pixel dimension you want

 

Facebook recommends:

  • Regular Photos: 720, 960 or 2048 pixels wide
  • Cover Photos: 851×315 pixels (under 100kb to avoid compression)

Instagram

  • 1080 pixels wide (up to 1350 pixels long)

500px

  • The bigger the better apparently, although a minimum of 2000 pixels wide is recommended

 

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