When you provide artwork to a print shop, you will often be given specifications for how that artwork should be saved and sent, including size, image resolution, file format, and a host of other details. We thought it might be appropriate to talk about some of the specs you should know before sending files in for print. We’re starting today by talking about image resolution.
At Its Most Basic
Wikipedia defines image resolution as “the detail an image holds.” It can be measured in many different ways, depending on what exactly you’re measuring, but for our purposes we are measuring resolution of images…mostly photographs, but it can also be for line art (like a logo).
You probably hear about resolution most when referred to as “megapixels”…as in, “How many megapixels does your new phone’s camera have?” More is always seen as better in those cases…because they are trying to sell products! We won’t spend much time dwelling on why more isn’t always better, but instead will say that the size you print something at will definitely be affected by the resolution.
Size Matters
If you take an image of a specific number of megapixels (measured by multiplying the number of pixels horizontally by the number vertically), you will get different results depending on what size you print it. The same Wikipedia page said it like this…
An image that is 2048 pixels in width and 1536 pixels in height has a total of 2048×1536 = 3,145,728 pixels or 3.1 megapixels. One could refer to it as 2048 by 1536 or a 3.1-megapixel image. The image would be a very low quality image (72ppi) if printed at about 28.5 inches wide, but a very good quality (300ppi) image if printed at about 7 inches wide.
So the same image can be printed at multiple sizes…but the results will vary wildly! For purposes of digital or offset printing, photos should be provided at 300 pixels per inch (ppi or dpi) or better for best results. If an image is natively 1-inch by 1-inch, it should be 300 pixels wide by 300 pixels tall. This would output well. If it’s 72 ppi, it will appear blurry or blocky.
“Great!” you say, “Then I’ll just increase the ppi in Photoshop!” That may help in some cases, but usually only when the resolution and photo quality was very good to begin with. Increasing the ppi in Photoshop (or another image editing program) forces the program to add pixels between what’s already there…interpolating the results. If the resolution was very low to begin with, the results are unlikely to be an improvement.
Line Art
You would be better providing line art (like your logo or an infographic) as vector art. Without going too much in the weeds, vector art is typically created in Illustrator or CorelDraw or another program like that. The shapes are created using math equations inside the code so they can be scaled up or down without losing any quality. When printed, they will automatically print at the maximum resolution of the device they are being printed on.
Sadly, a lot of companies don’t have immediate access to a vector version of their logo, though, so they send a PNG or JPG file of the logo. Those can work! But you really need to be careful of the resolution. If the resolution is 300 ppi, the logo will print alright…but if you have a 800 ppi version of it, it will print even better. Why doesn’t the same hold true for photos? Because line art is much more dependent on the edges being smooth and not blurry…something that’s usually not a problem in photos at 300 ppi.
One More Complication
There’s one additional factor to remember and that’s “effective resolution.” This is something that comes up when you place a photo inside another program (page layout programs are frequently a culprit…InDesign or Publisher) then resize the photo. “I took a 5 x 3 photo that was 300 ppi, dropped it into Publisher, and made it bigger…but now it’s not printing well!” That’s because the effective resolution dropped as you increased the size. The page layout programs generally do a poorer job of interpolating a photo larger than Photoshop does…and that’s rarely a good thing!
The inverse is also true, though. If you have a 8 x 10 photo at 150 ppi, drop it into InDesign and reduce the size by half…suddenly you have a 4 x 5 photo with an effective resolution of 300 ppi!
That Was a Lot!
I know…this little primer on image resolution got a little more complicated than I had intended, but it is important. We hate to see people wondering why their printed brochures don’t look amazing…”It looks awesome on my phone!!!” Hopefully you’ll be able to apply some of these thoughts to your next project before you bring it in to Print Cubes for production!