Hopefully you survived our last Quick Tip without nodding off to sleep. Getting into the details can seem boring, but trust me, when it comes time for you to know this stuff, you’ll be glad you brushed up.
So, where were we? Ah, yes. We sorted out just what type of image file we should be using for our project. Now we can get into the “good” stuff.
No, we’re not talking about the New Years Eve kind of resolution. We’re talking image size, and specifically, the size of a raster image.
Remember when we said that raster images (JPG, TIFF, GIF, etc.) are made up of tiny blocks, called pixels? The resolution of your image tells you how many pixels there are, in width and height, that make up that picture. A common resolution you see these days is 1920 x 1080 (also called 1080P), and it’s the resolution of a high-definition (HD) image. That means there are 1920 pixels going left to right and 1080 pixels up and down. There are many, many other resolutions of images, such as 1024 x 720, 320 x 240, or 1200 x 1200 (a common resolution for Facebook ad images), just to name a few.
So, the resolution of an image tells you just how many pixels are in it, but that’s not the whole “picture”.
To enjoy the beauty of our image, we must see it. That means displaying it somewhere, either on screen or in print. And that leads us to another critical detail, something called DPI (dots per inch) or PPI (pixels per inch). That’s designer lingo for figuring out the pixel density of the media you want to use to show off your picture.
Computer screens, digital projectors and LCD televisions have a display density of 72 DPI. That means that for roughly every inch of screen space, we need 72 pixels (or “dots”) of image to have it look nice and clear. If our picture is a 1920 x 1080 resolution, it will look fantastic on a 27” wide screen (1920 pixels divided by 72 pixels per inch = 26.6”).
Our photo looks amazing on the computer, so let’s grab our handy inkjet printer and whip out a 17” x 11” poster. If you’ve done this before, you know where I’m going. If not, well, you might be in for a shock. That picture, so crisp and clear on screen, is now fuzzy and blurry and looks horrible on paper. What did we do wrong? Well, it’s not totally our fault. It’s because printed materials have a different DPI than electronic displays do. We know our computer screen has a pixel density of 72 DPI, but our printer is very different. The minimum DPI for a basic inkjet is at least 300 DPI, and some can even go as high as 1200 or 2400 DPI.
If the printer has a pixel density of 300 DPI, then that 1920 x 1080 resolution image will only print clearly up to around 6.4” x 3.6” in size (1920 pixels divided by 300 pixels per inch = 6.4”). And if we try and force it to print larger, we quickly learn that raster images can’t create “new” pixels out of thin air, so they just “copy” the pixels around them, which makes them look blocky and we end up with blurry, yucky-looking image.
To have that picture print cleanly and clearly in on paper, you need to have around four times the resolution that you would for a screen display! For a 17” x 11” poster, your image would need to be 5100 x 3300 pixels. That’s a lot of dots! And like we said before, you can’t just make new pixels by resizing your image larger, so it’s important to always start with the highest resolution image possible for your project, and think ahead for what you might want to use that picture for down the road (i.e., brochures, wall graphics, vehicle wraps, etc.)
That’s a lot to absorb, so let’s take a break and we’ll come back next time to cover one final topic about images: Colour format. If you break out in a cold sweat just hearing the phrase CMYK, or if you think swatch books are only for picking out paint colours, we may have some tips for you.