Vector or raster: know what you have
Every artwork file is one of two kinds, and screen printing treats them differently.
| Vector | Raster | |
|---|---|---|
| What it is | Shapes defined by points and curves | A grid of colored pixels |
| Common formats | AI, EPS, SVG, PDF from a vector program | PSD, TIFF, PNG, JPG |
| Scaling | Any size with no loss | Only as large as its pixels allow |
| Best for | Logos, type, flat illustration, spot color | Photos, painted or textured art, simulated process |
| Watch for | A pasted photo inside an AI or PDF is still raster | Low resolution, JPG compression, white backgrounds |
A vector file separates cleanly because each color is already its own shape. A raster file can still print beautifully, but it has to be built at the right size from the start. A common trap is the "vector" file that is not: an AI, EPS or PDF that only contains an embedded image. Zoom in far; if edges turn into blocks, it is raster.
Resolution at print size
For raster artwork, the standard is 300 pixels per inch at the final print size. Do the math in pixels: a print 12 inches wide needs about 3,600 pixels across, and an image 1,200 pixels wide will only print 4 inches wide at full quality. Enlarging a small image in software adds pixels without adding detail, so edges go soft and halftones turn mushy. Images saved from websites, social posts or screenshots are almost always too small.
Build the art on a transparent background. A PNG with transparency or a layered PSD lets the printer see exactly what should print. Soft, semi-transparent edges, drop shadows and glows are not "free": screens either print ink or not, so those effects must be turned into halftones, which adds work and can look rough at small sizes. If a soft glow is not essential, remove it.
Fonts, lines and small detail
- Outline every font. Convert type to outlines (curves) before sending, or include the font files. A missing font gets substituted, and the wrong letterforms print.
- Expand strokes. Strokes can scale inconsistently between programs. Converting them to filled shapes locks the line weight.
- Respect minimum line weights. Fabric is coarse next to paper. One screen printed transfer maker's guidelines put the floor for flat ink at about 0.012 inch (roughly 0.3 mm) for a printed line and 0.04 inch (about 1 mm) for an open gap inside a filled area. Direct prints on textured blanks, fleece and heathers need more margin than that.
- Watch reversed detail. Thin lines and small text knocked out of a solid area, where the shirt color shows through the ink, fill in faster than printed lines do.
- Size detail for the placement. Art that works as a 12-inch full front may be unreadable as a 3.5-inch left chest. The print placement guide lists typical sizes.
Colors: name the inks
Screens show colors in RGB light, and printers mix ink, so color on a monitor is only a suggestion. Name each ink with a Pantone reference, and say whether it is a spot color to match or a general direction. Plastisol mixing systems usually publish formulas keyed to Pantone's solid color guides, which makes those references the common language. Bright on-screen colors such as electric green or hot pink may need fluorescent inks and still will not glow like a monitor.
Count the inks as part of the design, including white. Every ink is a screen, and screens drive cost: what drives screen printing cost shows how to drop a color without losing the look. If a design must print on several garment colors, say so up front, because the ink set may change with each.
What separations are
Separating a design means splitting it into one layer per ink. Each layer is output as a black-on-clear film (or printed straight onto the screen) where black means "ink goes here". Solid areas are solid black; lighter shades of an ink become halftone dots. A finished separation set also includes an underbase for dark garments, a highlight white if the design needs one, registration marks, and the print order.
How the art is split depends on its type. Clean logos get spot separations, one per color. Photo-like art gets simulated process channels on dark shirts or four-color process on white ones. The differences are explained in spot color vs simulated process vs CMYK.
Most printers do their own separations, because the right result depends on their mesh, inks, press and dryer, a link covered in mesh count and print feel. A designer can supply separated files, but expect the printer to adjust them.
Trap, choke and knockouts
Fabric stretches and screens flex, so colors never land in perfect registration on every shirt. Separators build in tolerance:
- Trap lets one color overlap its neighbor by a hair, usually the lighter color spreading under the darker, so a tiny shift does not open a gap of bare shirt between them.
- Butt registration means colors meet edge to edge with no overlap. It keeps ink thin but leaves no room for movement, so it is used carefully.
- Choke shrinks the underbase slightly inside the colors printed over it, so no white halo shows at the edges.
- Knockouts remove ink where it is not needed. On a black shirt, black areas of the art are usually left unprinted so the garment does the work, which saves a screen and keeps the print lighter.
These adjustments are tiny, typically a fraction of a millimeter, and they are part of why print-ready art from a designer is rarely sent straight to film.
Halftone settings
Halftones have settings: lines per inch (how fine the dots are), angle, dot shape, and the smallest and largest dot that will hold. These depend on the printer's mesh and press, so the best practice is to send continuous-tone art and let the separator set the halftone. The exception is a halftone used as a visible graphic element, such as big comic-book dots. Draw those as vector shapes at the exact size you want them to print.
What the printer sends back
Before production, expect three things to review:
- A mockup, showing the art on the chosen garment and color, at its planned size and position.
- A spec sheet or work order, listing the garment style and color, the size breakdown, each print location with its width and distance from the collar, the ink type, each ink's color reference, the number of screens and any special notes such as a soft hand. Its structure resembles a tech pack for decoration.
- For color- or placement-critical work, a strike-off, a real print on the real garment.
Check spelling, sizes, colors, quantities and placement on all of it. Approval is the point after which changes cost time and money, so read it like a contract. Embroidery has a parallel process; see embroidery digitizing explained.
Common file mistakes
- A logo pulled from a website or a social profile, far too small to print.
- Live fonts that were never outlined.
- A white box around the design that was meant to be transparent.
- Hairlines and thin strokes that shrink further when the art is scaled down.
- Gradients, glows and transparency in a design meant to print as solid spot colors.
- Colors described only in words, such as "the brand blue", with no reference.
- Art built at screen size rather than print size.
- Several versions sent without saying which is final.
- A raster image hidden inside a vector file format.
Sources
Useful for: clothing brands, bands, creators, companies.