The quick answer is, “Sure, but you probably won’t like it.” In Part 1 we covered the importance of good artwork. If you missed it, check it out here. Today we’ll talk about what kind of photo quality is necessary to create great-looking printed graphics. Getting the right photos for projects like wall murals and trade show graphics is often a challenge, but with a little understanding of the math and technology behind it, we can avoid a lot of the heartache.
Mommy, Where Do Digital Photos Come From?
Digital photos are created when your camera records the color and brightness of the light hitting each point on the camera’s sensor. The sensor is a grid of millions of points that we know as “pixels”; each pixel generates a large digital number that represents the color and brightness of what it saw at that moment in time. Digital cameras are rated by the number of pixels in the sensor; for example, my old iPhone is rated for 12 megapixels (MP), while professional-grade cameras are 20 MP to 60 MP. The iPhone produces photos that are 4032 pixels x 3024 pixels (4032 x 3024 = 12,192,768 pixels total, about 12 million or 12 MP).
All that data, however, results in a massive digital file, which limits storage and is hard to handle. So some smart guys came up with a process to compress the data by throwing out redundant data, limiting the number of colors, etc., and the JPEG (aka “JPG”) format was born. If you ever worked with bitmap (BMP) files for screen graphics, you know how JPG was a huge advancement for efficient graphic file management.
Why Do the Numbers Matter?
Here’s where the rubber meets the road, or in our case, the ink meets the paper. Most digital cameras store the image at either 72 dpi (dots per inch) or 96 dpi. In reality, the dpi of the digital file has no practical relevance for how your photo will look when printed – check out The Myth of DPI for a detailed (if slightly tedious) explanation of why.
What matters is how many dots per inch get printed on the page when you decide what size you want. At its native size, that iPhone photo will be 56 inches wide (4032/72 = 56) x 42” high, and each pixel will be 1/72” square. Believe it or not, that’s visible – in the photo of the measuring tape below, each division is 1/32”, and 1/72” is just smaller than half of that.
Also remember that in the compression process, a lot of the subtle changes from one pixel to the next were removed to make the file smaller. At best your photo will look a little blurry or grainy when printed at its native size.
Okay, now let’s enlarge that photo to 84” high to fill a wall (not quite, but we’ll keep the math simple). It’s still 3024 pixels high, but now it’s printing at 36 dpi. If you thought it looked rough before, this will hurt your eyes.
Commercial printers generally require artwork that will print at 300 dpi or higher on the page. Because wall murals are generally viewed from several feet away, we can get away with lower resolution… as we said above, at 72 dpi it will probably be a little blurry, and at 150 dpi it will be reasonably good.
My Friend Posted a Great Photo on Facebook…
Yeah, forget it. Digital photos are like tomatoes – every time they get handled and passed around, they get a little mushier. Actions like embedding in an email or a web page, and especially posting on social media, degrade the image simply to reduce the storage demands and make them transfer faster (i.e., load on the page). For example, I uploaded a photo to Facebook at 4032 x 3024, then downloaded the same photo at 960 x 720. Guess how well that will print.
Surely There Are Other Technical Solutions?
There is a process called “resampling”, usually done in Photoshop or similar software. Let’s say you want the photo doubled in size, but at the same resolution; Photoshop will essentially turn each pixel into four pixels, then take its best guess at how each new pixel should look. But it’s just a guess, and it’s the least effective in the places that need it the most: where the compression process created blurred edges. Resampling results can be good, or they can be very bad.
The next option is more for professional photographers. Higher quality cameras often have an option to take photos in the RAW format… this bypasses the compression process and stores all the original pixel data. The photo must be post-processed to get to a useful file format, but there’s more control over the compression process and there are other file formats available (such as TIFF) that don’t have the same problems as JPEG compression. On the other hand, the files are huge.
For the rest of us, the best solution is to pay attention to the file size. No matter what you might have heard otherwise when it comes to photos, bigger is always better. Back to the math: if you want a mural that is 12’ wide x 8’ high, we will get very good results from a photo file that is 21,600 pixels x 14,400 pixels.
Now I Get It – Where Do We Go From Here?
When you’re ready to get started on that large-scale project, or if you just have questions about all this, call us today at MetroCenter Signworks. Not only can we guide you through the development of your project and make sure the end result is great, but we also have several terrific sources for stock photos (like that shot of downtown Nashville at night that everyone wants on their office wall). Call 615-649-5003 or visit us at MetroCenterSignworks.com!