A 24 × 36 Inch Exhibition File for a Picky Lab

At 36 in wide, 8256 px gives 8256 ÷ 36 = 229 ppi (and 5504 ÷ 24 = 229 ppi), so the file is short of the lab's 300 ppi request by a factor of about 1.31.

At a 1 m viewing distance, human acuity is roughly 1 arcminute, about 0.3 mm on the print. A 229 ppi pixel is 0.11 mm, comfortably finer than the eye can resolve at that distance. The extra 300 ppi would not add visible detail; it would only satisfy a workflow convention. Upsampling cannot invent foliage detail and risks softening it.

Decision: supply the native 229 ppi file and ask the lab whether its RIP requires exactly 300 ppi or simply prefers it. If the RIP will resample automatically with an unknown algorithm, do the interpolation yourself in 16-bit with a good method, then sharpen for the final pixel dimensions. Never let an unchecked automatic resize make the sharpening decision for you. Confirm the crop is exactly 3:2 so no edge detail is lost at the trim.

Sharpening is size- and substrate-dependent, so the master stays unsharpened and the output step is applied to the resized file.

• Work at 100% on a calibrated screen and judge foliage and the sky gradient separately; foliage tolerates more, smooth sky reveals halos and banding immediately.
• For 229 ppi baryta, start modestly: amount around 80–120%, radius 0.6–0.8 px, threshold 2–4 to protect the sky. Avoid large-radius local-contrast moves on the gradient; they create mottling.
• Add a little fine grain or dither to the sky before printing if the 16-bit gradient shows stepping after conversion; baryta holds gradation well but banding is unrecoverable once printed.
• Print a test strip at final scale on the same paper: a crop of foliage and a crop of sky. View it at 1 m and at reading distance. Halos visible at reading distance are usually acceptable at 1 m; halos visible at 1 m are not.
• Adjust once, then apply the identical recipe to the final file and record the settings on the job sheet. Do not sharpen the web JPEG with the print recipe.

Print file: 16-bit TIFF, Adobe RGB or the lab's preferred wide space, tagged, with the lab's ICC profile embedded only if they request a converted file; otherwise send tagged RGB and let their RIP convert under the agreed profile. Soft proof first with relative colorimetric and black point compensation and check the sky for banding. Keep the paper white slightly below clipping - an OBA paper's base white is brighter than the screen suggests, so a file pushed to 255 loses the warm cast and any gradation. Name the file with job, size and profile, and state viewing assumptions in the notes.

Web file: convert to sRGB with perceptual intent, resize to 2000 px on the long edge, sharpen for screen at that size, save as a quality JPEG and check the reds and sky after conversion - saturated Adobe RGB colours can shift visibly.

Price-list print: 8 × 12 in at 300 ppi needs only 2400 × 3600 px; resize down from the master and re-sharpen with a smaller radius. For the OBA warning, tell the gallery the paper will appear cooler under daylight and warmer under tungsten, and advise consistent gallery lighting; supply a proof so they can judge in the actual space.