Printing restored photos at 300 dpi

What 300 dpi means

Dots per inch is how many pixels of the file are spread across each inch of paper. At 300 dpi, a print held at arm's length looks continuous; below about 150 dpi you start to see softness, and below 100 dpi the pixels themselves. So the size you can print is decided by the number of pixels in the file, not by anything the lab does. A 1,200 by 1,600 pixel photo, which is what many phone apps deliver, prints cleanly at about 10 by 13 cm and no larger.

The arithmetic is simple: centimetres divided by 2.54 gives inches, inches times 300 gives pixels. For 30 by 40 cm that is 3,543 by 4,724 pixels. For 50 by 70 cm it is 5,906 by 8,268 pixels. These are the sizes of the print files in the Family archive and Heirloom packs, made from 4K and 8K masters respectively.

• 30×40 cm at 300 dpi = 3543×4724 px
• 50×70 cm at 300 dpi = 5906×8268 px
• A4 at 300 dpi = 2480×3508 px
• 10×15 cm at 300 dpi = 1181×1772 px

Upscaling and what it should not do

An old print scanned at 300 dpi is small: a 9 by 13 cm original gives about 1,060 by 1,535 pixels. To reach 30 by 40 cm it has to be enlarged more than three times. Ordinary enlargement makes it soft; the restoration model reconstructs the fine texture of skin, hair and fabric instead, using the whole picture as reference. The rule that matters is that it must not reshape anything while it does this: eyes stay the same size, noses the same length, the smile the same width. The face-faithful upscale in the packs is designed around that constraint and the grain of the original is kept rather than smoothed away.

Which file to send to the lab

Send the print file, not the master and not the share card. The print file is already the right pixel size for its paper size, in sRGB colour, with no watermark. Labs accept JPEG; if yours asks for TIFF, most will convert on request. Do not let the lab's upload tool enhance or auto-correct the image; those settings are for snapshots and undo the tonal work. If the lab offers a choice of aspect ratio, pick the one matching the file so nothing is cropped from the edges.

Paper and finish

For a restored black-and-white or colourised photo, a matte or lustre paper shows the tone better than high gloss and does not reflect the room. Fine-art cotton papers give the softest look and suit portraits; a lustre photo paper is the safe default and cheaper. Ask for a small border rather than a borderless print; it makes framing easier and stops the edge of the image being trimmed. If the original was sepia-toned and you asked to keep it so, a warm-white paper is closer to the feel of the old print than a bright white.

Framing and hanging

Glass with a UV filter slows fading, which matters for colourised prints as much as for the originals. Keep the print out of direct sunlight and away from radiators. A mount board between the glass and the print keeps them from sticking in humid rooms, which is how many of the originals got damaged in the first place. If you are hanging a 50 by 70 cm print, have the framer cut the mount to leave a few centimetres around the image; a large photo of a face needs room.

Check before you order

Open the print file on the largest screen you have and look at 100 percent at the eyes and the hands, since that is where the viewer's eye will go on paper. If anything looks wrong, press redo before ordering the print; redos are free for fourteen days and the print file is remade from whichever version you choose. It is cheaper to redo the file than to reprint.