PPI, DPI, Pixel Resolution.. and Printing? *confused*

[h2k47]

Hello everyone,

   Yes, I know... This question had been asked probably a thousands time over the years by noobs and I have been trying to understand the way pixel and ppi and dpi 'thingies' work together by reading online but I have not been able to understand it completely.

What I want to know is, if I want to print a 1m x 1m poster for example, will it be enough that my image(which I downloaded from the internet) is for example 4000 x 4000 pixel ? Or I should be relying on something else for the poster to appear crispt and high quality??
When I type in  a pixel to meter calculator 4000p for example, it converts it to approx 1m, so is this all I need when I want to print a poster??

Thank you...

[ptoing]

PPI has nothing to do with print, it is how many pixels per inch are visible on a display.
DPI is the same for print, now many dots per inch are set by the printer, which mostly has to do with sharpness.

Most prints are done at 300dpi, so 4000 pixels would be about 13.3 inches which is a bit over 30cm. No idea how you got to it being 1 meter. That would require a much lesser dpi.

In general if you wanna make a pixelart poster it is a good idea to scale your pixels up in a clean fashion so that they are big enough to be printed to whatever size you want at 300dpi.

[h2k47]

Please let's make things simpler, I have a photoshop image ( 4000 x 4000 p ) and when i go to Image-> Image size, the pixel dimensions is 4000 x 4000 and under Document size, it is 141cm x 141 cm. and under resolution, it is 72 pixel/inch. How does all this relate to printing?

[ptoing]

72 dpi will not make for very high quality print. Tho if you want to print blown up pixels where you do not have much granularity anyway it might be enough.

The math here is 4000/72 = ~55.5inches which is about 141cm.

[h2k47]

So, if I would change the resolution value from 72 to 300 and check 'resample image' , would that be enough to make my image look sharp and crisp after printing even though my original image had 72 resolution?

In fact, I want to create a high quality print, so can I do that with any 4000p out there or would I need first to check if it is 4000p AND that it has 300 DPI?

[rikfuzz]

What you're actually looking at in photoshop's resolution input box is technically PPI (pixels/inch).  Same as with screens resolutions because they're measuring the same thing. 

DPI is used as a general term, which can be confusing, as it can either mean the same thing as PPI (commonly) or the dots/inch the printer uses to mix colours (which is obviously much higher, as each printed pixel needs to display a solid-looking colour made up of dots of 4 or so component colours).  Still most people saying DPI usually mean PPI (myself included) I've just tried to explain the ambiguity for clarification. 

You probably don't want to get into it, but LPI is used for how many lines of a halftone (ink mixing) pattern per inch.  If your printer lets you change the halftone LPI, you could experiment to lower it for stuff meant to be viewed from further away, to hide the pixelation.

55inches is quite large so 72ppi is probably enough, though up close you will see the pixels, so I would probably simply resize: with resample selected, and only change the resolution to 300ppi, so the bicubic filter can soften the edges of the pixels a bit.  This will change the pixel size, but not the physical size which is already what you want.