ALL IMAGE TOOLS56
Change Image DPI
Change Image DPI — Set 72, 150, 300 or 600 DPI
Rewrite a PNG or JPEG's print density without touching a pixel.
About Change Image DPI
DPI is the number a printer or a layout application reads to decide how large to print the pixels a file already has. It is metadata, not pixels: a 3000 by 2000 photo is a ten-inch print at 300 DPI and a forty-one-inch print at 72, and in both cases it is the same three thousand by two thousand pixels. That is why this tool never decodes your image. It edits the header fields in place — a PNG's pHYs chunk and, where the file carries one, its eXIf resolution tags; a JPEG's JFIF density and its EXIF resolution tags — and hands the same compressed image data back, so what you download is your file with a different number in it rather than a re-encode. Writing only one of a file's two fields is the classic way to get this wrong: where a JPEG carries both, readers believe the EXIF one, so setting the JFIF alone looks right in a preview and changes nothing in InDesign. A PNG that carries an eXIf chunk behaves the same way — measured here, not assumed, because writing pHYs alone on such a file is a silent no-op. Both fields are written, in both formats. The page also shows what a density means in practice, printing the physical size in inches and centimetres before and after, and it says plainly when a file declares no density at all rather than repeating the 72 that a reader would have invented on its behalf. PNG and JPEG only — WebP has no DPI field to change.
Questions
Will changing the DPI make my image bigger or smaller?
Not on screen and not in bytes. The pixel dimensions are untouched — the page shows them before and after so you can see that — and the file grows by at most 21 bytes when a PNG needs a pHYs chunk added, or 18 when a JPEG needs a JFIF segment. What changes is how large the picture comes out when something prints or places it.
I set 300 DPI but Photoshop still says 72. What happened?
An image can state its resolution in two places, and where the two disagree it is the second one a reader believes — a JPEG's Exif block outranks its JFIF density, and a PNG's eXIf chunk outranks its pHYs. Both were measured here rather than assumed. So a tool that writes only the first looks correct in a quick preview and changes nothing in a layout app; this one writes both, on both formats. The case it cannot fix is a file whose Exif block carries no resolution tags at all — adding one means relocating every offset inside that block — and when that happens the page says so instead of reporting a clean success.
Is my image re-compressed or re-encoded?
No. Nothing is decoded on the way out. The compressed image data — a PNG's IDAT chunks, a JPEG's scan — is copied through untouched, so there is no generation loss and no quality setting to get wrong. Only the header fields that state the density are rewritten, and the page lists which ones it wrote.
Can I change the DPI of a WebP?
No, and no tool honestly can. The WebP format has no resolution field: the one place a density could hide is a bolted-on EXIF chunk that WebP readers do not consult, so writing one would add bytes and change nothing. Drop a WebP here and the tool says that rather than pretending to work.
Which DPI should I pick?
72 and 96 are what screens and browsers assume, 150 is fine for a draft or an office printer, 300 is the usual commercial print target, and 600 suits line art and scanned text. The number only matters where something prints or places your image — a browser ignores it entirely, which is why the same file can look identical on screen at every setting.
Is my file uploaded to a server?
No. Transmute processes everything locally in your browser using JavaScript and WebAssembly. Your files never leave your device — there is no server, no upload, no cloud processing.