We look at most pictures on screens now, but preparing one for print is still an important skill. Get the size right and the print is sharp and vivid. Get it wrong and it is soft, blocky or cropped where you did not expect.
Resizing is about more than changing the dimensions. This guide explains resolution, the tools, the steps and the common pitfalls, for beginners and the more experienced alike.
Understanding resolution
DPI and PPI
The two terms are often used as if they meant the same thing. Strictly, PPI (pixels per inch) is how many of the image's pixels are spread across each inch of the print, and DPI (dots per inch) is how many dots of ink the printer lays down. For preparing a file, PPI is the number that matters.
For a print that will be looked at closely, aim for 300 PPI. A 3000 x 2400 pixel image prints crisply at 10 x 8 inches, because 3000 ÷ 300 = 10. Large prints, which are seen from further away, look good at 150 to 200 PPI.
Working out the pixels you need
Multiply the print size in inches by the PPI you want:
- Width in pixels = print width in inches × 300
- Height in pixels = print height in inches × 300
So a 7 x 5 inch photo needs 2100 x 1500 pixels. In metric, multiply centimetres by 118:
- Width in pixels = print width in cm × 118
- Height in pixels = print height in cm × 118
Common print sizes
| Print size | Pixels at 300 PPI |
|---|---|
| 6 x 4 inches (15.2 x 10.2cm) | 1800 x 1200 |
| 7 x 5 inches (17.8 x 12.7cm) | 2100 x 1500 |
| 10 x 8 inches (25.4 x 20.3cm) | 3000 x 2400 |
| A4 (21.0 x 29.7cm) | 2480 x 3508 |
| A3 (29.7 x 42.0cm) | 3508 x 4961 |
Aspect ratio
The aspect ratio is the proportion of width to height. If you change one without the other, the picture is stretched or squashed. Keep the 'constrain proportions' option, or the padlock symbol, switched on in your editing software.
A phone photo is usually 4:3 and a camera photo 3:2. A 10 x 8 inch print is 5:4. When the shapes differ, something has to be cropped, and it is better that you choose what.
Choosing the software
- Adobe Photoshop. The professional standard. Image Size lets you set dimensions and resolution together, with a choice of methods for reducing and enlarging.
- GIMP. A free, open-source editor with most of the same features.
- Canva and similar online tools. Simple, for quick adjustments.
- Your phone or computer's own photo app. Usually enough for cropping to a shape.
- Batch tools. Lightroom and XnConvert will resize many images at once.
Step by step
- Start with the original. Always begin with the largest, highest-resolution version of the photo, not one that has been sent through a messaging app or downloaded from social media, which will have been shrunk.
- Work on a copy. Keep the original untouched.
- Crop to the shape of the print. Set the crop tool to the aspect ratio you need, and position it so that nothing important is lost.
- Resize. Set the size and 300 PPI. For photographs, choose a bicubic method. 'Nearest neighbour' is only for pixel art.
- Sharpen lightly. Resizing softens a picture slightly. A little sharpening afterwards restores it.
- Save at high quality. See below.
Cropping or resizing?
Resizing changes how many pixels there are. Cropping changes the shape. Most prints need both. When you crop, the rule of thirds grid helps you place the subject well.
Colour
- Use sRGB for photo prints. Almost all photo printing services expect files in the sRGB colour space. Conversion to CMYK is for commercial press work, such as leaflets and brochures, and only when the printer asks for it.
- Expect prints to look darker. A screen is lit from behind and paper is not, so prints often look a little darker than the screen. Turning your screen brightness down when you edit gives a truer idea.
- Calibrate if it matters. For serious work, a hardware monitor calibrator makes the screen trustworthy.
- Test. Order one small print before a large or expensive one.
Common mistakes
Enlarging too far
A 1000 x 1000 pixel image cannot make a sharp 20 x 20 inch print. Software can enlarge a photo a little, and modern tools do it well, but they cannot create detail that was never recorded. If the file is small, print it small.
Saving at low quality
JPEG shrinks files by discarding detail. Save at the highest quality setting, and do not re-save the same JPEG over and over, because the loss builds up. TIFF and PNG lose nothing, but check that your printer accepts them.
Forgetting the edges
Printers trim a little from the edges, and a frame or mount covers a few millimetres more. Keep faces, text and signatures away from the edge of the picture.
Printing less wastefully
- Size the image correctly before sending it, to avoid reprints.
- Check a proof on screen, or one small test print, before a large order.
- Choose recycled or responsibly sourced paper where it is offered.
Conclusion
Good prints come from enough pixels, the right shape, sensible colour settings and a high-quality file. Get those right and the print will do your photo justice.
If you would rather leave it to us, our print and frame service prints your photo and frames it for you. EasyFrame offers a wide range of made-to-measure frames, and we can advise on the right one. Call us on 01234 856 501 or email sales@easyframe.co.uk. We are always happy to talk, whether or not you want to buy.