How to Prepare Images for Print: Size, Resolution and Quality

Print and screen are different jobs

A picture that looks perfect on a phone can look soft or blocky on paper. A screen shows an image at a fixed number of pixels, while a printer spreads the same pixels across a physical size, and the smaller each pixel is on paper, the sharper the result. Web optimization, which reduces pixels and quality to make files small, works against what print needs: as many pixels and as much detail as possible.

For this reason, a print file and a web file are two different deliverables. Keep the full-size original for print, and create small copies only for screens. The compressor on this page is made for the second job, and it is not the right tool to prepare your final print files.

How many pixels you need

The common rule for sharp prints viewed at arm's length is 300 pixels per inch, usually written as 300 DPI. Multiply the print size in inches by 300 to get the pixels you need. A 4 by 6 inch photo needs 1200 by 1800 pixels. An A4 page, which is about 8.27 by 11.69 inches, needs about 2480 by 3508 pixels. A 12 by 18 inch poster needs 3600 by 5400 pixels at 300 DPI.

Larger prints that people view from a distance, such as posters and banners, can use lower values, often 150 DPI or less, because the eye cannot resolve the dots at that distance. Your print provider can tell you the minimum for each product.

Check what your photo has

Compare the pixel dimensions of your photo with the numbers you calculated. A 12-megapixel phone photo of 4032 by 3024 pixels can be printed at 300 DPI up to about 13.4 by 10.1 inches, because 4032 divided by 300 is 13.44 and 3024 divided by 300 is 10.08. For smaller prints, you have plenty of pixels; for much larger prints, you may need to accept a lower DPI.

If you do not have enough pixels, enlarging the picture does not add real detail, because ordinary software only interpolates between the existing pixels, and AI upscaling can only guess the missing detail. It is better to take a new photo at a higher resolution, or to print smaller.

Compression and print

Lossy compression discards detail, and on paper the loss can be more visible than on a screen, especially in smooth gradients and fine textures. If you must send a JPEG to a printer, use a high quality, typically 90 or above, and avoid saving the file again several times. Better still, send the original file in the format that the print provider asks for, which may be a high-quality JPEG, a TIFF or a PDF.

If a print portal limits the upload size, check whether a quality of 85 to 90 with no resizing is enough to get below the limit. Avoid reducing the pixel dimensions below the requirement, since that costs print quality directly.

Color profiles and color modes

Screens use RGB colors, and most web pictures are in the sRGB color space. Many printers also accept sRGB, and some professional workflows use other profiles or CMYK, the four-ink mode of printing presses. Converting between them changes colors, because the range of colors that ink can reproduce is smaller than the range of a screen.

This tool removes embedded color profiles when it creates the compressed copy. For web pictures that is usually harmless, but for print and professional photography it can shift colors. This is another reason to use the original files for print work and the compressed copies only for screens.

Bleed, margins and cropping

Printers cut paper after printing, so artwork that must reach the edge needs a bleed, an extra margin of a few millimeters that is trimmed off. Important parts such as faces and text should stay inside a safe margin. The aspect ratio of your photo may not match the print size, for example a 3:2 photo on a 5 by 7 inch print, so decide what to crop before you order.

Cropping reduces the number of pixels, so recalculate the resolution after you crop. A tightly cropped photo may not be sharp enough for a large print.

A short checklist for print files

Start from the original file. Decide the print size and calculate the pixels at 300 DPI. Crop to the right aspect ratio. Keep the file in a high-quality format, with a JPEG quality of 90 or higher, or send a TIFF or PDF if asked. Do not use web-optimized copies. Follow the specification of your print provider, which overrides general advice.

Use the compressor for the screen versions: a preview for email, a picture for a website or a proof for a client. For those uses, a smaller file is exactly right.

Proofs and test prints

Before you order a large print run, order one small test print of the same file. Colors, brightness and sharpness on paper often differ from what you see on screen, and a test shows the difference for a few euros, instead of for the whole order. Look at the print in daylight, from the distance at which it will be viewed, and look closely at faces, skies and fine detail.

If something looks wrong, change one thing at a time, such as brightness, cropping or the file format, and print another test. Keep notes about what you changed, so that you can repeat the good result later and use the same settings for other pictures of the same series.