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Image DPI Changer

Set JPEG or PNG print-density metadata locally without resizing or re-encoding the actual image pixels.

This changes only the JPEG JFIF or PNG pHYs print-density metadata. It does not resize, crop, or re-encode pixels. PNG values use pixels per metre internally, so the displayed DPI can differ by a small rounding fraction.

Privacy: your files never leave your device. All processing happens locally in your browser.

How to use

  1. 1.Choose one JPEG or PNG image up to 25 MiB and review any detected print-density metadata.
  2. 2.Enter a whole-number target DPI; this value changes print metadata, not the pixel dimensions.
  3. 3.Select Update image DPI, download the copy, and verify its intended size in the destination layout or print application.

About Image DPI Changer

Image DPI Changer updates the print-density instruction stored in a JPEG or PNG without changing the image's pixel dimensions. Choose a file, enter a whole-number DPI value such as 72, 150, 300, or 600, and download a new copy. A 3000 by 2400 pixel image remains 3000 by 2400 pixels after the operation. At 300 DPI it has an intended print size of about 10 by 8 inches; at 150 DPI the same pixels have an intended print size of about 20 by 16 inches. Nothing is cropped, sharpened, enlarged, compressed, or uploaded to a server.

DPI is often misunderstood as a way to add detail. It is a print-density instruction: how many existing image pixels should be placed in each physical inch. Raising a value from 72 to 300 does not invent new pixels, improve a blurry photo, make web browsers render it more sharply, or turn a low-resolution scan into a high-resolution print. Lowering it does not delete pixels either. A printer, layout application, or export workflow may use the metadata to calculate a physical size, but a website normally displays an image according to its CSS or layout dimensions instead. Use an image resizer if the actual pixel count needs to change.

JPEG and PNG store this information differently. For a JPEG, this tool reads or writes the JFIF APP0 density fields and uses the standard dots-per-inch unit. If a JPEG has no JFIF density header, the output adds a small JFIF header. For a PNG, it writes the standard pHYs physical-pixel chunk using pixels per metre; the page converts the DPI value using the exact 0.0254 metre per inch relation. Integer pixels-per-metre storage means a PNG readback can differ from the requested DPI by a very small rounding fraction. That is a storage precision limit, not a change in the actual image pixels.

The page reports whether it found a usable existing JFIF or pHYs density. It also dynamically reads standard EXIF resolution fields after you choose a file, but it does not attempt to merge or rewrite every possible EXIF, XMP, ICC, IPTC, camera, GPS, or vendor extension. A JPEG can hold several forms of resolution information and applications may choose which one they display. The generated JFIF field and PNG pHYs field are documented, portable metadata for this focused operation; no output can force every downstream program to interpret print size in the same way. Test the downloaded image in the application or printer workflow that matters.

The input limit is 25 MiB and the tool accepts only JPEG and PNG. It validates the file signature and bounded header structure before it creates metadata. Truncated marker segments, malformed PNG chunks, duplicate physical-pixel chunks, or a pHYs chunk placed after image data are rejected rather than patched optimistically. The source pixels and compressed image data are copied as bytes, so the tool does not require a browser canvas and does not create a second lossy JPEG encoding. A failed operation clears its old result link instead of presenting a previous file as though it had just been updated.

For a practical print workflow, first decide the intended physical size, then calculate the DPI you need from the available pixels. A 3600 pixel wide image intended for a 12 inch print is 300 DPI. Set that value, download the copy, and place it in the target layout program at its intended size. Inspect small text, edges, and photos at final output dimensions; the metadata cannot compensate for insufficient source pixels. When a print provider specifies a pixel count, export profile, bleed, or file format, follow that provider's documented requirements rather than assuming a DPI label alone is enough.

This page does not convert image formats, change canvas size, preserve every possible metadata family, add print margins, estimate printer quality, or guarantee that a social platform will retain the value. It is a local metadata tool for a single exact purpose. Keep the original file, confirm the downloaded result in a metadata viewer or layout application, and use the DPI Converter when you need to work out a physical size before changing a file.

Methodology & sources

Validate a bounded JPEG or PNG header, dynamically inspect standard resolution metadata with exifr after selection, update or add JPEG JFIF units/Xdensity/Ydensity or PNG pHYs pixels-per-metre fields, preserve image bytes and dimensions, and create one local Blob download.

Frequently asked questions

Does changing DPI add resolution?
No. It changes a print-density instruction only; pixel dimensions and image detail stay the same.
Which formats can it update?
It writes JFIF density metadata in JPEG and pHYs physical-pixel metadata in PNG.
Why can a PNG show a slightly different DPI after download?
PNG stores an integer number of pixels per metre, so converting a requested DPI value can require a small rounding step.
Will every website or app use the new DPI?
No. Many web displays ignore print metadata, and programs can choose among different metadata families. Verify the destination workflow.

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