Image DPI Changer fixes the “please supply images at 300 DPI” request without touching your pixels. DPI is not image quality — it is a metadata note telling printers how densely to lay the existing pixels on paper. A 3000×2000 photo is the same photo at 72 or 300 DPI; only the intended print size changes (41 inches wide versus 10). This tool reads the resolution field inside the file — the pHYs chunk in a PNG, the JFIF density in a JPEG — and rewrites just those few bytes. There is no decoding, no recompression and no quality loss, which also makes it instant on any file size. The print-size preview shows exactly how large the image prints at the current and the new DPI, so you know before submitting whether the pixels are actually sufficient.
Features
Sets DPI in PNG and JPEG by editing the file's metadata bytes
Zero recompression — pixels are byte-identical after the change
Reads and displays the currently stored DPI, including “none set”
Print size preview in inches and centimetres at any DPI
Presets for 72, 96, 150, 300 and 600 DPI
Instant processing regardless of file size
Renamed output like photo-300dpi.jpg
Everything processed on your device
How to use the Image DPI Changer
Drop a PNG or JPEG
Check the stored DPI and current print size
Pick 300 (or any value) and check the new print size
Download — the pixels are untouched
Example
Input
3000×2000 photo at 72 dpi
Output
Same file at 300 dpi — prints 10×6.7 in instead of 41.7×27.8 in
Identical pixels; only the print instruction changed.
Common errors & troubleshooting
The image still looks the same on screen after the change. — It should — screens ignore DPI entirely and show pixels. The change matters only to printers and to submission systems that check the metadata field.
A print shop says the image is still low resolution. — DPI metadata cannot add pixels. If 300 DPI makes the print size smaller than needed, the image lacks resolution for that size — you need more pixels (a larger original), not a different DPI number.
The tool reports “none set” for a screenshot. — Many screenshots and web images simply omit the density field, and software then assumes 72 or 96. Setting an explicit value is exactly what submission systems checking for 300 DPI want.
A WebP or HEIC file is rejected. — Those formats store resolution differently and are rarely what print workflows ask for. Convert to PNG or JPEG first, then set the DPI here.
Frequently asked questions
Does changing DPI change image quality?
No. DPI is a print-density instruction stored in metadata; the pixel data is untouched here — not even recompressed. Quality changes only when pixels are resampled, which this tool deliberately never does.
What DPI do I need for printing?
300 DPI is the standard for photo prints and publications viewed at arm's length. Large posters viewed from distance work at 150, and billboards far less. Screen-only work conventionally sits at 72 or 96 — where the number is ignored anyway.
How large can my image print at 300 DPI?
Divide pixels by 300: a 3000×2000 photo prints 10×6.7 inches. The tool shows this for both the current and the proposed DPI, which is the fastest way to know whether your pixels meet a size requirement.
Why do journals and print shops ask for 300 DPI files?
Their systems read the metadata field to compute the intended print size and flag under-resolved images. Setting the field correctly — matched to a sufficient pixel count — is what makes the automated check pass.
Where is DPI stored inside the file?
PNG keeps physical-density values in a small chunk near the start of the file; JPEG stores density and units in its JFIF header. The tool rewrites exactly those bytes — with a correct checksum for PNG — and leaves the image data stream alone.
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