Change Image DPI - Free 300 DPI Converter Online

What Change DPI Does

DPI is not stored in the picture. It is a small number written into the file header that tells printing software how many of the image's pixels should be packed into one inch of paper. This tool edits that number and nothing else. For a JPG, the value lives in the JFIF APP0 segment, and often a second copy lives in the Exif block; both are updated so viewers agree with each other. For a PNG, it lives in the pHYs chunk, which stores pixels per metre rather than per inch, so the value is converted and the chunk's CRC checksum is recalculated. If a file has no such header, a correctly formed one is inserted. What matters is what is not touched: the compressed image data is copied through byte for byte. There is no decoding, no re-encoding, and no canvas involved, which is why the output file is almost always the exact same size as the input and why there is zero generation loss even if you run the same file through repeatedly. The consequence is worth stating plainly, because it is the single most common misunderstanding about DPI. Changing this number adds no pixels and removes none. It cannot make a blurry image sharp, it cannot add detail that was never captured, and it will not improve print quality on its own. A 600 by 600 pixel image tagged 300 DPI prints at 2 by 2 inches; tag the identical file 72 DPI and it prints at roughly 8.33 by 8.33 inches. Same pixels, same file size, different instruction to the printer.