Resize Image to 4x6 Photo Size

What 4x6 Means in Pixels

Inches measure paper and pixels measure files, and DPI is the exchange rate between the two. At 300 dots per inch, the density photo labs print at, 4 inches is 1200 pixels and 6 inches is 1800, so a 4 x 6 print wants a 1200 x 1800 file - about 2.2 megapixels. 300 is not arbitrary: it is roughly the point where printed dots stop being separable at reading distance, and it is the figure nearly every kiosk and mail-order lab quotes. Send fewer pixels than that and the lab enlarges the file for you, with no say from you in how. The harder problem is shape. A 4 x 6 print is 2:3. Phone cameras mostly shoot 4:3, mirrorless and DSLR bodies shoot 3:2, and anything cropped for a social feed is square or 4:5, so only the 3:2 files drop straight in. A 3024 x 4032 phone portrait scaled to fit lands at 1200 x 1600 inside the 1800-pixel-tall frame, leaving 100 pixels of background above and 100 below, a third of an inch of border on each. The same photo scaled to fill lands at 1350 x 1800, and 150 pixels of width - about a tenth of the picture - are cut away. Turn the camera sideways and the arithmetic turns severe, because this frame stays portrait: a 4032 x 3024 landscape shot fills it only after half its width is discarded, and fits inside it only as a 1200 x 900 strip with a 450 pixel band of background above it and another below. Half the print is picture and half is border. That symmetry is the reason the fit selector exists at all - the pixels have to come from somewhere, and the only question is whether they come out of the photograph or out of the paper. Enlargement is the other thing worth watching. 2.2 megapixels is modest, so an original camera file has pixels to spare, but a copy returned by a chat app, a download from a social feed or a screenshot often does not. A 1080 x 1440 image has to grow by 10 to 25 percent depending on the fit, which nobody sees on paper. A 480 x 640 thumbnail has to grow between two and a half and nearly three times, which everybody does. Interpolation cannot recover detail a sensor never recorded, so the factor is reported rather than quietly applied. Decoding, cropping and encoding all happen on the canvas element inside your own browser, so the photo is never uploaded.