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Beyond the Screen: DPI and PPI in Photo Printing

by Catherine Ramsey (follow)
Blog (395)      Articles (166)     
Understanding PPI
PPI stands for pixels per inch, which sounds pretty self-explanatory. The acronym PPI is only ever used to describe images on a screen, as pixels are a digital term.

As youíve probably gathered, the more pixels you have per inch, the closer you can zoom into that image. If you open up an image in Photoshop and zoom really far in, youíll actually be able to see the defined pixels appear, and eventually a grid will show, like in the picture below. Notice also, that the rulers to the top and left of your workspace show how big 1 inch appears.



DPI PPI photography printing mean definition



DPI PPI photography printing mean definition


When we check the image size properties in Photoshop, we can see that this photo has a resolution of 72 Pixels/Inch.



DPI PPI photography printing mean definition


Understanding DPI
Similarly, DPI stands for dots per inch and refers only to printing. Itís important to make the distinction between PPI and DPI, because they are in fact used for different things, despite people often using them interchangeably.

If youíve ever looked closely at a newspaper or catalogue, youíll notice that the print is often made up of a series of tiny dots, rather than solid as they appear on a screen. Donít worry if you donít see it, you may need to look under a magnifying glass to see it properly.



DPI PPI photography printing mean definition


When ink is printed onto a surface, the image is made up of thousands of tiny dots, and as youíve probably guessed, there are a set number of dots per inch. The more dots per inch, the thicker or more solid the print will look, without the noticeable ink speckles.

But, just because a photo is to be printed large, doesnít necessarily mean it needs more dots per inch. One might expect that a billboard, being such a large print, would need a really high number of dots per inch, but in fact, billboards generally have a very small number of dots per inch. The reason for this is that billboards are always viewed from a distance, where you canít see each individual dot.

The print doesnít need to be as dense as, say, a fine art photo, which may be observed at very close range and requires a high quality finish.



DPI PPI photography printing mean definition


Image size
Now something that confuses a lot of people is image size. Letís take another look at the first image:



DPI PPI photography printing mean definition


We can see from the image size properties that the width of the entire image is 2250 pixels, and the height is 1500 pixels.

If we wanted to change the size, say, to make it smaller for uploading to the web, we could change the width or the height (but not both, as these will remain in a fixed ratio). Take a look at the dialogue box now:



DPI PPI photography printing mean definition


Youíll see that Iíve changed the width to be 1200 pixels across. The image now appears smaller, although the resolution size remains the same. This is because no matter what image size we change it to, this photo will always have a resolution of 72 pixels per inch (unless we change this also, but more on that later).

Resolution rules
Digital monitors always have a fixed number of pixels per inch. This can never be changed. If youíre only ever going to view your images on a screen (or display them on a website), you really donít need to worry about having a high PPI count. Most people upload images to the web at 72 PPI, and thatís all thatís required. But even if you uploaded images at 600 PPI, it wouldnít matter one way or another, because itís not possible to view more pixels per inch than your monitor allows.

DPI, on the other hand, does matter... if youíre planning on printing your images. It is recommended that print material be saved with at least 300 DPI. Keep this in mind when exporting your files.



DPI PPI photography printing mean definition


Pro tip: Youíve probably realised by now that the more dots per inch used, the more ink is used also. When printing from a home printer, youíll probably want to go no higher than 300 DPI. For professional shop printing it should be fine to go higher than this.

One last issue that I wanted to cover is changing the resolution of an image. I mentioned this briefly above.

If we take a photo, fresh from the memory card, chances are its resolution will be automatically set to 300 DPI, which means that this photo is already print ready. If we wanted to make the resolution smaller, for digital use, we can do that, no harm! I would suggest choosing a standard resolution size of either 96 PPI or 72 PPI.

However, if we take a photo from the web, whose resolution is already fixed at 72 PPI, we canít actually increase its resolution size to make it more suitable for printing. Letís take a look at what happens:

This photo that Iíve pulled off the web, has a small image size of only 525 pixels wide and 350 pixels high. Its resolution is 72 PPI.



DPI PPI photography printing mean definition


If I wanted to print this photo into a large canvas sized print to go on my wall, I couldnít do it without a huge loss in quality. We canít simply change the resolution to be print ready at 300 PPI.



DPI PPI photography printing mean definition


Notice how blurry and pixelated the image becomes?

The same thing happens again when we leave the resolution at 72 PPI, but change the image size to 3000 pixels wide.



DPI PPI photography printing mean definition


What Iíve proven to you now is that you canít just take any small image and print it as big as youíd like, and expect quality results. Make a large image smaller, but donít make a small image larger!

Usually the size that an image is when it comes off of your memory card, is the best size that it needs to be to print it large. So if you know youíre planning on printing your photo at some point, donít change the image size or resolution, save it as it is, itís as simple as that!


Displaying your work
If youíve managed to make it through understanding PPI and DPI, and youíre not ready to tear your hair out, congratulations!

Before going any further, you may want to also read up about lab printing, screen calibration, and colour spaces on our blog.

Itís time to display your artwork with pride. And by following the tips above, you should be able to ensure top quality prints every time. So what are some professional ways that you can display your work for others (and you) to enjoy?

A classic framed photo print is always a good choice:



DPI PPI photography printing mean definition


You may want to consider different paper choices to suit your artwork.

A matte photo paper will give a slightly raised, textural finish. It helps to combat reflective glare, which is awesome for rooms with a lot of lights. It does, however, reduce the luminosity of your print and can make photos appear darker than how youíd normally view them on a screen. Itís well suited to black and white printing.

Lustre prints will give the best luminosity, for bright and beautiful, smooth prints with lots of colour. However, as you can probably guess, this paper type produces a lot of glare.

Some labs have special luminous effect papers that make your image look almost as though they were lit from behind with a lightbox. Ask instore at your nearest professional lab for a paper sample.



DPI PPI photography printing mean definition


Perhaps a large wall-length canvas is more your cup of tea? Just remember that careful image size and resolution choice is vital here!

Photo books are currently all the rage. And why not? Theyíre professional looking and make you feel like youíre a published author. I canít deny that Iíve turned a few of my travel journals into neatly presented photo books to share with friends and family.



DPI PPI photography printing mean definition


A few of my favourite photo book publishers are Blurb and Momento. I feel they have a more professional touch than Big W or Snapfish.

If youíre of the arty persuasion, perhaps youíd like to let loose and collage a wall!



DPI PPI photography printing mean definition


I hope now youíll feel confident enough to release those photos from the prison of a memory card or hard drive. But as always, if you have any questions, feel free to get in touch via the Photoh Facebook page, groups or Instagram.

Catherine
Photographer and instructor at our regular Night Photography classes in Brisbane.

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