PDF Image Resolution (DPI) Checker
Check the effective resolution (DPI) of every image placed in a PDF's pages, with pixel dimensions and placed size, reported per placement rather than per image.
Tool workspace
Nothing is uploaded. Files are read in this tab and stay on your machine.
List placed images and their resolution
How do I check the DPI of images in a PDF?
Select one PDF. The document structure is read in this tab; no image is decoded.
Read the completeness line first. It says whether every page was read to the end.
Check the per-placement table for pixel size, placed size and effective resolution.
How is effective image resolution calculated?
Check the resolution (DPI) of every raster image (photo or scan) placed in a PDF's page content, including inside nested forms: its pixel dimensions, the size it is placed at on the page, and the effective resolution that results. Resolution is reported per placement, because the same image placed at two sizes has two different resolutions.
An image in a PDF is drawn into a unit square and mapped onto the page by a transformation matrix. Its effective resolution is its pixel count divided by the physical size it was mapped to, so one image used forty times at different scales has forty different answers. The placed size is measured along the transformed axes, which stays correct under rotation, mirroring and skew where reading two matrix entries would not. The figure shown is the lower of the horizontal and vertical values, because that is the one that limits how the image reproduces. The page's UserUnit, which some very large drawings declare, is applied to both the placed size and the resolution. Checking resolution before a set goes out for review, in Xenmark or elsewhere, saves a round of comments about unreadable scans.
How Xenmark makes it easy to check image resolution in a PDF
Effective dpi for every placement
Each time an image is placed, its pixel count is divided by the size it is drawn at, so a logo used at three sizes gets three answers.
Nothing leaves your machine
Nothing is uploaded. Files are read in this tab and processed in memory, with no account and no server for them to go to.
Read from the structure, no image decoded
The report comes from the document's own image references, so a very large scan is listed exactly like a small one and is never drawn.
Images inside forms and layers included
Placements nested inside form objects are followed, and each row notes when an image is mirrored, clipped or sits on a named layer.
Tells you whether the count is complete
A completeness line states whether every page was read and every image reference resolved, and names what stopped it when that is not the case.
Nothing to install
It runs in the browser you already have. There is no plug-in, no desktop application and no sign-up to get through first.
Limitations
What this tool does not do, stated up front.
Images inside comments, stamps and other annotations, and images used as pattern fills, are not listed. No resolution is given to vector content or to a page as a whole.
A placement with no area, or an image that declares no usable pixel dimensions, reports no resolution. That is not a resolution of zero and is counted separately.
An encrypted PDF is refused outright rather than partly inventoried, because this tool reads the file structure directly and does not decrypt it. Files over 64 MiB are refused too.
Questions
Why does the same image appear more than once?
Because it is placed more than once. Each placement has its own size on the page and therefore its own effective resolution. The image itself is counted once in the object total.
How do I find low-resolution images in a PDF?
Load the PDF and read the summary line, which gives the lowest and highest effective dpi; every placement is then listed with its own figure. A low figure is the usual reason an image prints blurry. No image is decoded and the PDF is not changed.
Why does my 300 dpi scan show a different number?
Because effective resolution depends on the size the image is drawn at. The same pixels placed larger give a lower figure and placed smaller a higher one, so a 300 dpi scan that was enlarged or shrunk on the sheet no longer reads 300.
Why did Xenmark build a free image resolution checker?
Xenmark AS is a Norwegian software company building browser-based drawing review tools for owners, consultants, operators and other teams that receive and review technical drawings. Those teams handle PDFs every day, and not every file should be sent to a website just to merge, split or check it — a tender document, a client’s drawing set, a revision that is not released yet. So these everyday tools are free and run entirely in your browser: no account, no upload step, and no server ever receives the file. You can check that yourself — open your browser’s network tab, inspect a scanned set, and watch nothing leave. What this tool cannot do is listed under Limitations above.
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