# Need to know the size for printing a poster

I'm new to DPI and all the stuff, and the fact is that I want to print a poster, at the image of 16 meters on 8 meters.

Now, I've contacted our printing center, and it seems that I have 2 possible options:

1. Deliver a file on real-size at 300 DPI, but this means files of 40 Gb or more, is this correct?

2. Another option is to find a vectorial image so that it can be scaled without an issue.

But, I do want to have a skyline (a picture), but does pictures do really exists as vector images? If so, where can I find them, paid or free doesn't matter.

Kind regards,

• I think the assumption that you need 300 DPI is not correct. The required DPI depends on the viewing distance, and that distance is very different for a 16x8m banner compared to a 4x6cm photo print. Here's a previous question which might be helpful. Commented Nov 15, 2014 at 13:19

I'm guessing, based on their response, that your printing center is not familiar with billboard printing, or they would have given you more helpful advice.

Christina Galbiati wrote a web article on this subject - Designing large scale projects—trade shows and billboards: beginner tips and tricks (4/5/2013) - and offers some helpful information on this subject.

This article includes basic information on how to scale your image to the correct print size at the correct DPI. DPI is the printer's resolution in dots per inch.

I'm assuming that a 16m x 8m print is going to be viewed at a very far distance, so you can expect that the needed DPI is going to be much lower than if it is being viewed close up. Everything should scale proportionally, so if the image at 16inch x 8inch with 300 DPI print resolution looks good viewed from 2 feet way, then scaling up to a 16m x 8m (a factor of 39.4) print will look fine at about 79 feet (2 feet x 39.4) viewing distance with a resolution of less than 7.6 DPI. (Thats 300 DPI / 39.4).

But you really need to discuss this with someone who has experience with scaling for large presentations. They will tell you what part of this process you need to do and what part they will do. They will also tell you of any hidden gotchas that aren't obvious to those who don't print murals on a regular basis.

Note - apparently a link to the cited article is not allowed here, but you should be able to google it with the information given.

• You can have links, just as long they only contain supplementary info. The text of your answer should be able to stand on its own. Commented Nov 15, 2014 at 18:42

Raster images are what is produced by a camera, they're simply a recording of color at position. So a 300 DPI print is 300 color points per inch, which may or may not be necessary for what you need. The size of the image file required depends on the size of the print, and how many inches are you filling with 300 dots. (300 dots • width in inches = required width in px)

How are you planning to take a photograph that large anyway? You can't just scale it up; if you take, say, a 2000 by 2000 px image, plop it in Photoshop, and scale it to 2,000 by 2,000 px you haven't made the image any larger, just spread the same amount of detail out over more pixels. You've got a 6" wide print at 300DPI, or a 66" print at 30DPI.

Vector images are composed of mathematical definitions of shapes. Letters, for example, are vector: the shape of a Helvetica "R" can be printed at 10px wide or 10,000 px wide because it has a mathematical definition that is used to create a raster image (your screen itself is a raster image because it has a set, limited number of pixels) at any resolution.

However, just because vector images are mathematically defined and infinitely scalable, does not mean you can magically take a vector image with infinite detail. Detail and sharpness (around the edges of shapes) are different. In fact, if you used a computer algorithm to convert a photo into a vector image, you would lose detail, but the detail you retain would have crisp edges around each color area at any resolution.

In short: cameras take raster images, there's only so much size in a photo—there's no magic to make a really high quality print from a low resolution image. Take the resolution from your camera, find how large you can print at different DPI, and find what size and detail you want based on viewing distance and file size; 300 is not a magic number.

First off, "DPI" doesn't mean anything in this context- the correct term is "PPI", or pixels per inch. DPI refers to how close together a printer can put different droplets of ink, which in your case is irrelevant.

300 PPI is a rule of thumb for what's as good as you'll ever need for a normal sized print viewed at a "normal" distance. (The actual number is derived from a complicated formula). For an image printed at 16 x 8 meters, you need nowhere near 300 PPI because no one is going to be looking at it from a "normal" viewing distance. It's at least one whole order of magnitude wrong.

Did your printer actually tell you that he needs a file that big? Call back and double check the 300 PPI. If he still insists on 300 PPI image, find someone else.

IIRC Keith Cooper at http://www.northlight-images.co.uk/ has some experience in printing that big, so you might want to check out his articles and ask him for advice.

• DPI is a correct term, just beyond the detail we're going to in either of our answers.
– Ryan
Commented Nov 15, 2014 at 17:34