Preflight Check for Color, Fonts and Hairlines
A PDF can look correct on your screen while depending on unavailable glyphs, mixed color spaces or strokes too fine for the chosen process. Read the actual objects before deciding whether a compatibility repair is safe.
Open the PDF Preflight Checker ↗Start with a known geometry.
Color and typography reviews still depend on the right trim. An embedded font does not protect a phone number sitting 1.2 mm from the cutting line. Check the red trim, blue bleed and green safe overlays first. The A6 example supplies a known reference: 105 × 148 mm trim, 3 mm outer bleed and properly embedded text.
The business-card sample isolates a different problem. Its trim is 252 × 144 points, or 3.5 × 2 inches. Helvetica is referenced without an embedded font program and its border measures 0.10 pt. Viewing that document successfully on one machine is not evidence that another renderer has the intended font or preserves the thin line.
Use the six-check PDF preflight workstation to locate those objects, then use the image-placement DPI checker for actual raster dimensions. The full on-screen lists remain free. A limited proof is useful for discussion, while the formal audit pack records the complete object list and remaining warnings.
Use the dimensions.
Keep the units.
300 DPI: physical size to pixels
Pixels = millimeters ÷ 25.4 × 300, rounded to the nearest whole pixel. These dimensions refer to the trim, before adding any bleed. A different placement size changes effective DPI even when the underlying pixels are unchanged.
| Finished format | Trim in mm | Pixels at 300 DPI |
|---|---|---|
| A4 | 210 × 297 | 2,480 × 3,508 |
| A5 | 148 × 210 | 1,748 × 2,480 |
| US Letter | 215.9 × 279.4 | 2,550 × 3,300 |
| Business card | 88.9 × 50.8 | 1,050 × 600 |
| A6 postcard | 105 × 148 | 1,240 × 1,748 |
| A2 poster | 420 × 594 | 4,961 × 7,016 |
Bleed and safety: keep the directions separate
Bleed extends outward; the safe margin sits inward. The numerical targets below are inspection examples. A book cover, folded piece, bound page or large-format print must use its actual job template. KDP spine and safety requirements cannot be inferred from the example’s fixed dimensions.
| Example | Bleed per edge | PDF points | Safe-area instruction |
|---|---|---|---|
| Commercial example | 3 mm / 0.11811 in | 8.504 pt | 3 mm inward, illustrative job target |
| US commercial example | 3.175 mm / 0.125 in | 9 pt | 0.125 in inward, illustrative job target |
| KDP cover example | 3.175 mm / 0.125 in | 9 pt | Use the exact cover template, including spine |
| Large-format example | 5 mm / 0.19685 in | 14.173 pt | Ask the print shop; finishing varies |
The 142 DPI brochure calculation is 710 pixels ÷ (360 points ÷ 72) = 142 DPI horizontally. Vertically, 426 ÷ (216 ÷ 72) also equals 142. The passing sample’s 600 × 300 pixel placement at 144 × 72 points gives 300 × 300 DPI. A page-size table cannot replace this per-placement calculation.
Changing the target alters the classification rather than the measurement. A 150 × 300 DPI placement fails a 300 DPI minimum on its first axis but meets a 150 DPI target on both. A rotated 300 DPI image remains 300 DPI because rotation preserves the transformed basis lengths. An enclosing rectangle is unsuitable for calculating that resolution.
Programs, colorants and physical strokes.
Keep these properties separate
| Object or state | What is actually reported | Production question |
|---|---|---|
| RGB / Lab | Detected object color space and page location | Which output profile and rendering intent? |
| CMYK / Gray | Process or neutral resource identity | Correct press condition and ink handling? |
| Spot / Separation | Named separation resource, distinct from process CMYK | Retain the named ink or authorize conversion? |
| Embedded / non-subset | Actual FontFile program presence; valid without a subset prefix | Does the print workflow accept this program? |
| Subset / unembedded | Subset name and embedding are checked independently | Is the original program actually available? |
| Type3 | Glyph programs identified, with a separate compatibility review | Does the receiving RIP support this use? |
Fully embedded, non-subset fonts are not automatically missing fonts. Conversely, a six-letter subset prefix does not prove program presence. The inspector follows the font descriptor and checks FontFile, FontFile2 or FontFile3. Type3 uses glyph programs rather than a conventional external font file, so it is identified separately and still merits compatibility review.
RGB and Lab findings are output-policy warnings rather than proof that the design is unusable. Correct conversion depends on the press profile, substrate and intended appearance. Spot colors require a deliberate separation decision. This browser tool does not claim to run a desktop ICC conversion or spot-separation system, and it does not silently replace a named ink.
Hairline sampling at 300 and 600 DPI
Raster pixels across a physical stroke equal points ÷ 72 × DPI. The table uses the original physical line width, before antialiasing. Nonuniform graphics transforms can make the effective stroke narrower. A measured width exactly equal to your threshold is not classified as below it.
| Stroke | Pixels at 300 DPI | Pixels at 600 DPI | At 0.25 pt target |
|---|---|---|---|
| 0.10 pt | 0.417 px | 0.833 px | Below target |
| 0.25 pt | 1.042 px | 2.083 px | Meets target |
| 0.50 pt | 2.083 px | 4.167 px | Meets target |
| 1.00 pt | 4.167 px | 8.333 px | Meets target |
Flattening can resolve some transparency compatibility problems, but it cannot recover an unavailable original glyph or manufacture photographic detail. K=100 black and rich black also have different colorant behavior. A single RGB raster cannot honestly claim retained vector CMYK overprint. Font sources, output ICC policy and overprint acceptance must be agreed before a production repair is supplied.
Use the color and font reference alongside the print-ready checklist. Confirm the original source, not only the preview. A paid report preserves FAIL or WARN when those findings remain; purchasing a report never creates a printer approval.
Specific answers.
Useful limits.
What do TrimBox, BleedBox and SafeZone mean?
TrimBox is the finished cut rectangle. BleedBox describes extra artwork outside it. SafeZone is an inspection margin inside trim, not an official PDF page box. At a 3 mm target, a 105 × 148 mm trim has a 111 × 154 mm bleed extent and a 99 × 142 mm safe rectangle.
How many pixels do I need for an A4 image at 300 DPI?
Multiply millimeters by 300 and divide by 25.4. An A4 trim of 210 × 297 mm rounds to 2480 × 3508 pixels. A full-page raster including 3 mm bleed measures 216 × 303 mm, approximately 2551 × 3579 pixels. These are pixel dimensions, not an instruction to rescale the trim.
Can every RGB object simply be converted to CMYK?
No universal conversion produces the right result for every press, stock or ink limit. Ask for the required output profile and rendering intent. Spot colors can require retained separations. This tool identifies color resources and warnings; it does not offer a cloud ICC or spot-separation engine.
Is a subset font name proof that the font is embedded?
No. A six-letter prefix describes a naming convention. The inspector separately checks for a font program in FontFile, FontFile2 or FontFile3. A fully embedded non-subset font is also embedded. Type3 contains glyph programs and is reported separately for compatibility review.
Why is a 0.10 pt line risky?
At 300 DPI, 0.10 points occupies approximately 0.417 raster pixels before antialiasing. At 600 DPI it occupies 0.833 pixels. The published 0.25 pt target corresponds to about 1.042 and 2.083 pixels respectively. Actual line survival also depends on transformation, plate, substrate and printer tolerances.
Is pure K=100 black the same as rich black?
No. K=100 uses the black component alone; mixed or rich black adds other colorants. Black text can need a particular overprint treatment, while white objects should not blindly inherit it. A flattened RGB page does not preserve vector CMYK overprint semantics. The printer must define the intended output policy.
Can raster flattening recover a missing original font?
No. If the original font is unavailable, the renderer may lack the intended glyph shapes. A 300 or 600 DPI bitmap only samples what the renderer actually draws. Re-export with the original font embedded, or use a separately authorized substitution with an agreed visual reference.
Does this calculate the spine for my paperback?
No. The sample spine is a fixed illustrative 0.50 in, between two 6 × 9 in panels. Real cover width depends on the printer’s current template, page count and paper type. Use that template and inspect the resulting PDF rather than copying the sample’s spine dimension.
What happens to the PDF when I close the tab?
The application releases its in-memory source, decoded objects and raster previews. It does not persist a customer project in browser storage, a database or a file bucket. A full-page navigation requires selecting the source again. Free inspection never sends PDF contents or filenames to a server.
Why does a paid inspection report still say FAIL?
The report records measured findings, not a purchased approval. A 142 DPI photograph remains below a 300 DPI target even if a bleed proposal looks correct. The full inspection pack retains every issue, original page dimensions and source fingerprint. Print acceptance remains with the receiving shop.