Printing Photoshop file at high DPI? What about PPI?

Hi everybody!!!

I am sure is not the first time someone here ask questions about digital imaging PPI and DPI, but I am one of those who still struggling to understand this theory. Here is my question and would be immensely thankful for your input!!!!!

1) I am printing some Photoshop files on a high resolution printer (HP Z3200 COMERCIAL PRINTER: Up to 2400 x 1200 optimized dpi from 1200 x 1200 input dpi with maximum detail selected). Does it mean that I need to set my Photoshop file to 1200/2400 dpi to get best quality prints on this printer? I am a bit confused when I hear that anything more than 350 dpi is overkill, at the same time printers specifications have their dpi much higher at 1200/2400. If 400 or 500 dpi is overkill why printers today claim to have output up to 2400 dpi?

2) I also have read quite a few articles on websites that talk about the relationship of PPI and DPI trying to figure out the best PPI and DPI combination for the size work I am producing in Photoshop. So far I still not sure at which DPI / PPI I should be working with. The image I am working right now is set at (PIXEL DIMENSIONS: Width: 6337 - Height: 5639 / DOCUMENT SIZE Width: 18 inches - Height: 16 inches at 350 DPI). The only hint that I am getting that this maybe a overkill is that the document is pretty heavy, but not sure if true.
Anyone can give me some tips on the above file settings or direct me to a easy website that explain DPI and PPI so I can figure out

THNAKS A LOT!!
Andy

I am not an authority on this but I'll give it my best shot.

DPI (dots per inch) and PPI (pixels per inch) are basically the same thing. There is another measurement used for preparing work for commercial printing or creating files for magazines to print called LPI (lines per inch). LPI is roughly PPI x 2.

What kinds of things are you printing, or planning to print on this commercial printer?

Do you own this HP commercial printer? If so, you could do some tests printing images at different resolutions. 300ppi should be adequate I should think. But if you can see a noticeable difference in the output then this is what is important.

In one sense, pay zero attention to the printers resolution information. Especially the interpolated (the 2400 dpi) information.

Are you printing this image at 18" in width? If so, the 350 dpi is perfect for an image at 6337 ppi in width.

The formula is (width in ppi) / dpi. So at 6337 / 350 = 18.10. Which is a one to one correspondence between the dpi (printer dots per inch) and the pixel dimensions (pixels per inch) across 18" of the paper.

If on the other hand, you are intending on printing the image say 10" in width, then you are placing more pixels per inch (PPI) in the image than the printer will resolve (DPI) onto paper--it will "throw" some of the pixels away.

Your printer can handle 24" width, correct? So put it this way, leaving aside the .20" border and using the full 24" width as borderless printing, the maximum PPI of an image that you are going to be holding one foot from your face is needed to be 28800 ppi across the width (1200 dpi x 24 inch wide paper). More PPI than that is a waste, less than that is going to begin to get pixelated. The DPI of the image means little to nothing to the print device. All that matters is the pixel dimensions.

Now, the DPI does matter to applications that read this little 5 byte piece of information in the file--but it is only information and means nothing in reality. It is used to aid the user of software to load and display a given image at a given size and calculate when one deviates from a one-to-one PPI of the file. In other words, pixels have no size. A pixel can be as little as one printer dot (DPI) or 10 printer dots (and more). Never less than one printer dot. But once a pixel (PPI) begins to take up more than one printer dot, an image can begin what we would call pixelated. It isn't, however, until a single pixel takes up X number of dots that the eye begins to notice. The "X" depends on the resolution of the printer.

LPI (lines per inch) is a film screen measurement that applies to a traditional offset press printing system.

Take care, Mike