Vector and raster: the distinction everything else hangs on
Raster images (JPEG, PNG, photos, most Canva exports) are grids of pixels — they have a fixed amount of detail, and enlarging them stretches that detail thinner. Vector artwork (AI, EPS, SVG, most logo source files) is mathematical shapes — it scales to any size with perfectly clean edges.
For logos, text, and flat graphics, vector is what you want, because output size stops mattering. Photographic artwork is inherently raster, which is fine — it just makes resolution the thing to check. The practical skill is recognising what you've actually been sent: a vector file with an embedded screenshot inside it is a raster job wearing a vector extension.
Resolution only means something at output size
"300 DPI" on its own is not a specification — DPI is pixels divided by printed inches, so it changes the moment the print size changes. A 1500-pixel-wide image is 300 DPI at 5 inches wide and 75 DPI at 20 inches. The question is never "what DPI is the file?" but "how many pixels is it, and how big will it print?".
Around 300 DPI at final size is the common working standard for close-viewed garment and small-format work; large-format output viewed from distance tolerates far less. When a file falls short, upscaling adds pixels but not detail — it turns crisp-but-small into large-but-soft. The honest options are: get a bigger original, reduce the print size, or set expectations with the customer before printing.
Colour: RGB, CMYK, and why screens lie
Screens make colour with light (RGB); most printing makes colour with ink (CMYK, plus white or spot colours in some processes). RGB can display vivid greens, oranges, and electric blues that ink physically cannot reproduce — so files usually arrive in RGB, and something converts them before output. The conversion is where the customer's neon green quietly becomes moss.
The defence is not "always convert everything to CMYK immediately" — modern workflows and RIPs handle conversion, and some (DTF included) print from RGB pipelines with wide-gamut ink sets. The defence is reviewing what the conversion does before committing ink, and never promising a colour from what a phone screen shows. For brand colours, get a reference (Pantone or an approved previous print) — "match our blue" without a reference is a dispute on a timer.
Fonts, transparency, and the invisible faults
Fonts: a design file references fonts by name, and a machine without that font substitutes another silently. The finished goods then carry a typeface the customer never chose. The fix is asking for text converted to outlines/curves (turning letters into shapes), or the font files supplied alongside. It's a ten-second export step for the designer and an unfixable fault after printing.
Transparency: artwork destined for garments usually needs a genuinely transparent background. Two faults hide here — a white background that's invisible against a white canvas in preview but prints as a solid box, and a fringe of semi-transparent edge pixels left over from auto-removal tools that prints as a pale halo. Both are caught by previewing the file against a dark background, which takes five seconds.
These checks — format, resolution at size, colour review, fonts, transparency — are the core of a preflight pass. The artwork preflight checklist turns them into a printable routine your whole team can run the same way every time.