File prep for large format: resolution, bleed, and the mistakes that cost a day
Most large-format reprints are caused by four fixable things in the file. Here is what to check before you send artwork for a banner, a poster or a booth graphic.
Work at final size, or at a clean fraction of it
The single most useful habit in wide-format artwork is building the document at the finished size, or at an exact fraction like a quarter or a tenth, rather than at an arbitrary size you intend to scale later. It makes every other decision checkable: text size is real text size, margins are real margins, and resolution means something.
If the piece is genuinely enormous, a 1:10 document is easier to handle and scales cleanly. What causes trouble is a file built at some incidental size that has to be scaled by an odd factor, because every measurement then has to be recalculated and small errors compound.
Resolution is measured at the size it prints, not the size it was made
A raster image has a fixed number of pixels. Stretching it does not create detail, it just spreads the same pixels across more inches. That is why a logo that looks perfect on a website can look soft on a 3-foot banner even though nothing about the file changed.
For large format, roughly 150 dpi at the final printed size is a workable target, and you can go lower on something viewed from across a car park. What matters is the arithmetic: an image that is 1,200 pixels wide gives you 8 inches at 150 dpi. It does not give you 4 feet at any usable quality.
Vector artwork sidesteps the problem entirely because it is drawn from mathematics rather than pixels, and it scales to any size without loss. Logos, type and flat graphic shapes should be vector wherever the original exists.
Bleed, and the material that disappears into a hem
Bleed is extra artwork past the trim line so that a slight cutting variance does not leave a white sliver at the edge. On small commercial print an eighth of an inch is standard. On large format it needs to be much larger, and on anything hemmed it needs to be larger still.
A welded hem folds material back on itself, so an inch or two of the printed face disappears around the edge before the banner is even hung. A pole pocket takes several inches. A gallery-wrapped canvas loses an inch and a half to two inches on every side around the stretcher bar. In each case the fix is the same: extend the background into that zone deliberately, and keep logos, faces and text well inside it.
Colour: what will and will not match
Screens emit light and printers reflect it, so a colour that glows on a monitor may look flat on a matte vinyl. That is physics, not a printing error. The colours most affected are saturated blues, bright oranges and any neon.
The practical answer is to specify brand colours as named spot values rather than eyeballing them, and to say up front if a specific colour has to match something already in the field, such as an existing sign or a vehicle. A printed proof is the only way to actually confirm a colour, and it is far cheaper than a reprint.
It is also worth knowing that the same file printed on gloss vinyl, matte fabric and corrugated plastic will not look identical on all three. Different substrates absorb ink differently. If a set has to match across materials, say so before the job runs.
Fonts, layers and the files nobody can open
Send a PDF unless you have been asked for something else. Outline the type or embed the fonts, because a missing font substitutes silently and the first anybody notices is when the proof comes back in the wrong typeface.
Flatten transparency effects, or export in a format that handles them predictably. Native design files with linked images are a common failure: the layout arrives and the images do not, because the links pointed at a folder on someone else's desktop. Package the job or export a self-contained PDF.
A short checklist
Built at final size or a clean fraction. Raster content at roughly 150 dpi at that size. Logos and type in vector. Generous bleed, larger again for hems, pockets and wraps. Live content pulled well inside the finished edge. Fonts outlined or embedded. Images embedded, not linked. Brand colours specified rather than sampled by eye.
Nothing on that list is exotic. Almost every large-format reprint traces back to one of them. Our artwork and file guidelines page covers the general case across all categories, and the large format printing and banners and signs pages list the substrates and finishing this applies to.