Colorize a Photo for Printing — Pro, on our server
Same pixels in, same pixels out — plan the print from that. The colorizer is a chroma operation: it predicts colour for each region and leaves the light-and-dark structure, the dimensions and the framing untouched, handing back a lossless PNG of exactly the size you uploaded. Nothing is invented at the edges and no resolution appears from nowhere. So the print size is already fixed by your scan: divide width and height by 300 for a photographic print viewed in the hand, or by roughly 150 for something that will hang on a wall and be seen from a couple of feet away. A 2400 × 3000 pixel scan is a comfortable 8 × 10 inches at 300 DPI and a perfectly reasonable 16 × 20 inch canvas. Doing that arithmetic before you upload saves both a disappointing order and a wasted run.
Colour first, size second — the order genuinely matters. Enlarging a grey scan and then colorizing it wastes your 24-megapixel input budget on interpolated pixels and gives the model no more real information than it started with. Colorizing first and enlarging second gives the upscaler chroma edges to follow as well as luminance edges, which is more to work with. The upscaler is free and runs on your own device; Pro accounts can also switch on the Cloud HD ×4 mode, which uses HAT-L on our GPU, accepts inputs up to 4 megapixels, produces up to 16× the pixels of the input — a 4 MP photo comes back at about 64 MP, and takes four to five minutes on a 4 MP input. A ×4 Cloud HD upscale is an HD run, of which each plan includes ten a month alongside the ordinary allowance.
Prepare the file properly before it goes anywhere. Scan at 600 DPI for small prints so there are real pixels to work with, then crop to the image itself with the crop tool — a scanner-bed border eats into both the megapixel limit and the print composition. If the master scan is over 25 MB, the compressor will bring it under while keeping the pixel dimensions, and both of those tools run inside your browser. When the lab wants a JPEG or a TIFF rather than a PNG, make that copy with the converter and archive the PNG as the master. If the print is destined to be framed and the original has a crease running through it, deal with that before colour — the old photos page covers why colorization leaves damage exactly where it found it.
Expect ink to be duller than a screen, and order a test. A monitor emits light across a wide gamut; a printer lays down ink with a narrower one, so saturated blues, greens and deep reds routinely lose a little intensity on paper. That is not a defect in the colorization — it is the same gap every photographer manages — and the fix is the same as it has always been: a small test print before a large order, and a lab whose profile you have seen before. On the privacy side, this is a Cloud HD tool, so the photograph is uploaded to our server for one run, encrypted in transit, processed in the United States, deleted when the run finishes and in all cases within 24 hours, and never used to train anything. The cropping, compressing, converting and on-device upscaling around it never leave your machine.