Difference between document size and print size

[silk1975]

Hello everyone.

I have a problem i can't really explain.

In Photoshop, i create a document that is (for example) 68cm x 23cm at 300dpi.

When i send it to my printer, i keep the actual size in the parameters (68x23/300) , the image size on the paper is somethink like 64,6 x 22,3.

I really dont know where i do wrong. In Photoshop my document has the good size, and in my printer parameters for that image, whatever i do like "use document size", or force it manually to the same parameters i have in PS, the image size is printed wrong...

What am i missing ?

Thanks 🙂

[Derek Cross]

You seem to be mixing Pixels per inch with Pixels per centimeter 

(And it's PPI, not DPI)

[D Fosse]

What you have to understand is that Photoshop doesn't work with sizes. It works only with pixels. Pixels have no size, they are just data points.

The print size is determined (much) later, by using the simple formula pixels per inch (ppi).

Pixels per inch means exactly what it says. There's no hidden meaning. How many pixels to an inch of paper, that's it. Pixel density determines print size. Obviously, to get good visual quality, you need a certain minimum pixel density, which is why you can only blow up an image to a certain point.

In other words, as size goes up, ppi goes down. And vice versa. But it's the same image.

Perceived pixel density depends on the viewing distance. That's why the same image can be used as a magazine spread at 300 ppi, or a roadside billboard at 10 ppi.

[Bojan Živković]

"whatever i do like "use document size", or force it manually to the same parameters i have in PS, the image size is printed wrong..."

Difficult to say without inspecting options in your printer dialogue. It seems something is preventing you to print dimensions you want to print despite configuration. What it can be? Already mentioned pixel density or some option which is turned on but not easily visible to you. 

[Piet Bel]

My best guess here would be that your printer driver is actually preventing you from properly printing your document at the right size, but we would need some additional data or test to make be sure. 

What you could do is to export your psd file to PDF (or Tiff, jpeg or soming similar for that matter). Inspect that document and see if it has the correct sizes (68 x 23 @300DPI). If so; you might wanna try and print that, to see if the issue remains.

If the issue remains, I'm positive that it is your printer (driver), if not; let us know so we can check if the issue has something to do with PPI, DPI or any other parameter or adjustment.