PPI belongs to the image placement
An image that is 3000 pixels wide and printed six inches wide has 500 pixels per inch across that edge. If it is printed twelve inches wide, it has 250 PPI. The file can remain exactly the same while the physical placement changes.
The calculation uses the pixels that survive the crop. A 6000 × 4000 landscape photograph filling a 10 × 8 inch frame retains 5000 × 4000 pixels. Dividing by the frame dimensions gives 500 PPI in both directions. Using the original 6000-pixel width would describe a different placement.
DPI belongs to the output device
A printer reproduces the image through its own marking process. Its dots are not interchangeable with the source image’s pixels. Printer resolution settings describe that device process; they do not prove that the photo contains a corresponding number of independent image samples.
Read the printer and paper instructions when choosing output settings. A number advertised for a printer is not a target that you must enter as the photograph’s PPI. PrintLilt reports image geometry and pixel density; it does not control ink placement or substitute for the driver.
Why a file may still say DPI
Some applications label an image-resolution field as DPI even when the practical calculation is pixels per inch. Interpret the value in context. If changing it leaves the pixel width and height unchanged, it has not created new image detail.
A resolution tag can suggest a default physical size to software that reads it. Other software may use its own page or scale settings. For a physical photo layout, check the image rectangle and the PDF page dimensions, then use actual-size printing. Do not rely solely on a tag in the raster file.
A comparison with the same photo
Suppose a 4000 × 3000 image must go into a 10 × 8 inch frame. Fill retains 3750 × 3000 pixels and gives 375 PPI. Keep the whole photo places it at 10 × 7.5 inches, gives 400 PPI, and leaves a quarter-inch border above and below.
The printer can use the same device resolution setting for either layout. The different PPI values arise from how the image is fitted, not from a change to the printer’s dot mechanism. This is why image PPI and printer DPI should remain separate fields in your reasoning.
Choose settings that answer the right question
Use the pixel dimensions and intended print size to evaluate the image. Use the printer documentation to select the medium and output mode. Use a small physical test to judge sharpness and colour when the result matters. A high number in one part of the workflow cannot compensate automatically for a problem elsewhere.
PrintLilt’s PPI examples are comparisons, not pass marks. A lower-density large display may serve its purpose, while a higher-density file with poor focus may disappoint. Keep the original and compare the actual output rather than repeatedly rewriting the resolution field.