How is image resolution calculated, and why isn’t it the image’s own DPI?

The DPI stored in an image file means nothing once it’s in a PDF; print sharpness depends on pixels divided by the size the image is placed at. A 600-pixel-wide image placed 2 inches wide is 300 dpi, but scaled to 4 inches it’s only 150 dpi. Every placement is tracked, so an image used at different sizes on different pages is reported separately. Offset printing usually wants 300 dpi; digital printing is fine around 200 dpi.

Why does it say there isn’t enough bleed?

Bleed is artwork that extends past the trim line — usually 3 mm per edge — so small cutting errors don’t leave white edges. The tool compares the TrimBox (finished size) with the BleedBox (or CropBox) on each edge. If the file has no TrimBox the page itself is treated as the finished size, so bleed is zero. Export from your layout app with “Use document bleed settings” and crop marks enabled.

Is RGB colour always a problem?

No. Digital presses and office printers convert RGB automatically, so those profiles only note it. Offset printing separates into CMYK, and vivid RGB colours — bright greens and blues especially — can turn noticeably duller, so convert with your printer’s ICC profile and proof first. Black text is best set as 100% K rather than RGB black or four-colour black.

Does this replace the print shop’s preflight, and is my file uploaded?

It catches most common problems, but it doesn’t flatten transparency, preview separations or measure ink in image pixels, and it can’t replace a professional RIP preflight — your printer’s feedback has the final word. All analysis runs in your browser and the PDF is never uploaded.

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🛫PDF Preflight Check - Bleed, Image DPI, CMYK & Fonts Online

The worst time to discover blurry photos, white slivers at the trim, shifted colours or substituted fonts is after the job is printed. This tool preflights a PDF in your browser by reading its low-level structure page by page. It reads the MediaBox, CropBox, TrimBox and BleedBox, works out how many millimetres of bleed each edge has, and checks that the boxes nest correctly and trim sizes match. It follows the transformation matrix of every image placement in the content streams and divides pixels by the placed size to get the effective resolution — the same image scaled up on another page is reported separately, and 1-bit line art is held to a higher standard. It records the colour spaces used by vector art, text and images on each page, separating RGB, CMYK, grey, Lab, ICC-based colour and Separation / DeviceN spot colours; checks font embedding, including the standard 14 fonts and Type3; flags transparency (opacity, soft masks, blend modes, transparency groups), overprint and white objects set to overprint that would vanish in print; finds hairlines thinner than a threshold or with zero width; estimates the maximum total ink of vector CMYK colours; lists annotations without the Print flag, annotations a RIP will ignore and form fields that should be flattened; and reads encryption permissions, the output intent and PDF/X or PDF/A claims, plus whether the page count suits duplex or saddle-stitch binding. Offset, digital print and office printer profiles are built in, with editable thresholds. Results are graded as errors, warnings and notes; click one to outline the image, line or annotation on a rendered page, or mark every image with its dpi. Export the report as HTML or CSV for your designer or print shop. The file is read locally and never uploaded.

Free · No sign-up · Runs in your browserLast updated: 2026-10-26

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How to use PDF Preflight Check

1Pick a profile (offset, digital print or office printer) and adjust the dpi, bleed, hairline and binding settings if needed
2Upload a PDF to see errors, warnings and notes plus each page’s size, bleed, colour spaces, transparency and ink
3Click “Show on page” to locate a problem, then export the HTML or CSV report

FAQ

How is image resolution calculated, and why isn’t it the image’s own DPI?: The DPI stored in an image file means nothing once it’s in a PDF; print sharpness depends on pixels divided by the size the image is placed at. A 600-pixel-wide image placed 2 inches wide is 300 dpi, but scaled to 4 inches it’s only 150 dpi. Every placement is tracked, so an image used at different sizes on different pages is reported separately. Offset printing usually wants 300 dpi; digital printing is fine around 200 dpi.
Why does it say there isn’t enough bleed?: Bleed is artwork that extends past the trim line — usually 3 mm per edge — so small cutting errors don’t leave white edges. The tool compares the TrimBox (finished size) with the BleedBox (or CropBox) on each edge. If the file has no TrimBox the page itself is treated as the finished size, so bleed is zero. Export from your layout app with “Use document bleed settings” and crop marks enabled.
Is RGB colour always a problem?: No. Digital presses and office printers convert RGB automatically, so those profiles only note it. Offset printing separates into CMYK, and vivid RGB colours — bright greens and blues especially — can turn noticeably duller, so convert with your printer’s ICC profile and proof first. Black text is best set as 100% K rather than RGB black or four-colour black.
Does this replace the print shop’s preflight, and is my file uploaded?: It catches most common problems, but it doesn’t flatten transparency, preview separations or measure ink in image pixels, and it can’t replace a professional RIP preflight — your printer’s feedback has the final word. All analysis runs in your browser and the PDF is never uploaded.