Blowing it up

Putting your photo on a billboard is extreme, but not impossible. To fit the common board size, where each centimetre of your photo becomes 1,25 metres, use a photo that has 600 pixels per inch and is 12 inches (30 cm) wide and 4 inches (10 cm) high.
Photograph by Getty Images
Date:17 February 2013 Tags:, , ,

How to enlarge and print your digital photos.
By Rob Sheppard

The picture of your puppy looks great on your phone – so good, in fact, that it would be even better in plain view on your wall. And bigger, too! Not just 10 x 15 or even 20 x 25, but really big. So how giant can you make it before the digital image starts to break down?

The answer depends on how the photo was taken and how the print will be created.
Variables include the camera sensor, the printer and the photo itself. You can easily generate prints up to 33 x 48 cm using a camera with a 10-megapixel sensor to capture the image. With some practice and the right photos, you might even be able to go that big from a 6-megapixel camera.

The maths behind those not-quite-hard-and-fast rules all comes down to a single measurement: pixels (or dots) per inch – dpi. A high-quality print requires a resolution of 300 dpi. That means 300 pixels in each linear inch (horizontal or vertical), not 300 pixels in each square inch; a 300-dpi, 1 x 1-inch image is 300 pixels high and 300 pixels wide. As such, a 6-megapixel image taken at the same aspect ratio as 35-mm film (2:3) is 3 000 pixels wide and 2 000 pixels high. To determine how wide you can safely make the image, divide 3 000 by 300. The result indicates that you can make a print of a high-quality 6-megapixel image that’s up to 10 inches (25 cm) wide and 6,67 inches (17 cm) high.

If you push your photo too far size-wise, it will be easy to tell. Photos printed larger than they should be will come out fuzzy, with ill-defined edges. Onscreen, giant pixels are the sign of an image that’s been enlarged too much; when printed, those pixels become blurry, since printer software is designed to always produce a smooth photo.

From camera to computer

Regardless of the camera you use, there’s a lot you can do to produce images that will stand up to being enlarged. In general, shoot using your camera’s highest quality JPEG mode, which adds sharpening, noise reduction, and other fine adjustments. The way you shoot the photo is just as important as the camera’s settings. No matter how big you make your print, the image has to be in focus. Use a tripod and a fast shutter speed to reduce the amount of movement the camera captures.

Before sending your photo to either a home printer or a lab, you need to process it. Adobe programs – Photoshop and Photoshop Lightroom – have become industry standards, but they’re pricey.

First make sure your image is in the right colour mode, RGB. Even though printers generally print using CMYK inks – cyan, magenta, yellow and black – they’re designed to process RGB files, which appear more true to life onscreen because monitors project colours in red, green and blue. Next, get your image to the right size using your software’s resize option, and make sure you’re setting the image size at the specific resolution you want.

Then you can move on to adjusting the tone and contrast. For images to print well, they typically need a full range of tones, from pure black to pure white. To achieve that, you’ll use an adjustment often called levels, which shows a histogram of the tones in your image. Drag the black slider until you just begin to see blacks showing up and do the same with the white slider and whites. Then you can adjust the midtones with the slider in the middle, moving it until the midtones are just that – in the middle of black and white.

Now that you’ve fine-tuned the range, you can adjust contrast. You might be drawn to the simplicity of the contrast and brightness sliders, and if these are the only contrast adjustments your software offers, you can make do. But it’s better to use curves, where you’re less likely to overdo the contrast. In curves, you’ll see a straight line that you can pull and push to get the contrast just right. A good rule of thumb is to make the line into a soft S curve. But, as with levels, it pays to experiment.

From screen to paper

Just as important as the camera and image processing is the printer. Epson and Canon both make affordable, high-quality consumer printers that can create images up to 33 x 48 cm; we like the Epson Artisan 1430 (R6 900)* and Stylus Photo R3000 (R10 000)*, as well as the Canon Pixma Pro-10 (R14 300)*. In addition to printing large photos in the traditional 35-mm aspect ratio – 2 x 3, which means up to 30 x 45 cm – the Epson printers can also create panoramas up to 33 x 112 cm. These printers use between six and 10 inks, while conventional printers use just four. The wider range of colours helps specialised printers achieve a broader range of colour and tone.

If 33 x 480 cm isn’t big enough for you, then you might want a large-format pro-level printer such as the Epson Stylus Pro 3880 (R13 000)* or the Canon imagePROGRAF iPF5100 (R22 000)*, both of which can print photos as large as 43 x 55 cm. Epson’s model uses eight inks, while Canon’s has 12. Another option is to have photos printed professionally.

The paper is important, too. Glossy paper makes for the sharpest, most colourful prints. But semi-gloss and lustre offer nearly as sharp images with less shine. Many of the highest quality papers are produced by specialised paper companies. Be sure to tell your printer what kind of paper you’re using in the print dialogue box.

*Prices at time of print.

Give it to the pros

What if you just want one or two large-format photos? In that case, buying a printer is overkill, and you’ll want to go to a local pro lab. There are also Web-based services that do fine work, and they are often cheaper than pro labs. But with that price comes the advantage of working with the printer in person to get the most from your image. All printers vary, so if you choose a local service, visit the lab to check out a sample print from one of your images.

Judging your print

Even if you’ve processed your photo like a pro, it may come out looking different to the way it does onscreen. A monitor displays white light filtered through coloured pixels, and a print shows ambient light reflected off coloured dots on paper, so an exact reproduction of what you see onscreen is impossible. After you’ve printed it, take the photo away from the computer and consider whether it looks good on its own.

Every Pixel Counts

Each photo is made of a set number of pixels. Therefore, the larger you make a photo, the fewer pixels there are in each square of a set size, be it a square inch or square centimetre. Here, our original photo, a shot from an iPhone 3, was compressed from 2 megapixels to a smaller €file size for e-mail, which left it just 864 pixels wide and 1294 pixels high.

7 x 11 cm (300 dpi) – For the largest print that remains sharp, set a photo’s resolution to 300 dpi.

78 x 117 cm (28 ppi) – When the photo is too big, there aren’t enough pixels to maintain sharpness. This 2,5 x 2,5 cm square contains just 28 x 28 pixels.