3 Myths of PPI (Pixels Per Inch)

There are so many myths about PPI (Pixels Per Inch) perpetuated by both photographers and printing companies that just cause confusion and extra effort for no benefit!

Myth 1: You should use 72PPI for web images

Repeat after me:

PPI does not affect file size
PPI does not affect file size
PPI does not affect file size

Ok, so I mentioned it three times. But, it’s important, it’s the one myth I see propagated more than any other! There are a few things that have an impact on the filesize of your image. The content, the compression and the size in pixels. A 3000 pixel wide image, set at 72PPI, has the exact same information as a 3000 pixel wide image set at 300PPI, or 10000PPI if you want! The only thing the PPI does is set the default print size if you were to not specify a size when you’re printing. So, a 3000 pixel wide image, set at 72PPI, would as a default print at 41.7″ wide.

Your PPI is actually set at the time of printing – if you print a 3000 pixel wide image at 10″, then the number of Pixels Per Inch is 300. Regardless of what you’ve set in the file.

Which obviously means, that as well as not saving filesize – it does not protect your images from being taken from your website and printed. If you want to stop people from being able to do that you have 3 real options:

Upload low resolution files
Use an intrusive watermark
Don’t upload any images

The only time the PPI setting on Lightroom or Photoshop will do anything is when you specify a size in physical dimensions, as well as a PPI setting. But please be careful when using these settings, as increasing the size of an image, does not make it higher quality – see Myth 3.

Myth 2: PPI and DPI are the same thing

PPI is the number of pixels your image is wide, divided by the print size in inches.

Dots Per Inch, (DPI) is a physical property of whatever printer it’s being printed on, you can’t change it. But these terms tend to be used interchangeably.

OK, so this one doesn’t really matter.. But I thought I’d mention it anyway.

Myth 3: Everything should be printed at 300PPI

This is one that’s perpetuated by a few big printing companies which tell you if an image is “ok”, “good” or “excellent” when you upload it. Generally only telling it’s the highest quality when it’s set at 300PPI.

Well, 300 is great, and it’s what I always make sure my images are when printing in a normal size. But what about enlargements, big canvases and the like? Surely you want them to be 300PPI to?

Well, a 40″ wide canvas would need to be 12,000 pixels wide. Which would mean you’d need a 96 Megapixel camera. Know anyone with one of those? Nope, Me neither.

So you have two choices, you can either re-sample the image using Photoshop (if you don’t know how, feel free to ask), accept having a lower PPI, or a combination of both. A full, non-cropped image from my camera (Nikon D750) is 6016 pixels wide. So at 40″ this would be 150.4 Pixels Per Inch.

Sounds low quality? Well, if it was a small 6″ x 4″ print it possibly would be, because you’d be viewing it from close up. But the further away you stand from an image, the lower the Pixels Per Inch has to be. But it’s 40″ wide, so you’re going to view it from a difference.

Think about those flash new Quad HD / 4K HD Televisions that are now becoming the norm, a 40″ one of those only has a PPI of 96. So that 150 PPI canvas is actually a higher resolution than a 4K TV!

Bottom line – ignore the guides on those websites, trust your photographer if they tell you it’ll print fine as an enlargement 🙂

If you do want to re-size, just resize it in Photoshop and make sure you’re re-sampling it – but remember Photoshop is just interpolating, creating additional pixels based on the pixels around it, so you won’t gain any real quality. I doubt you could even tell the difference between a 40″ image printed at 150PPI and one upscaled from 150PPI – 300PPI and