Digital Printing Online

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What image file size do I need for poster printing?

We aim to provide some helpful explanations and tips to navigate the world of digital printing and simplify the language used.

What image file size do I need for poster printing?

what image file size do I need for a successful poster print

When planning for printing a large format image as a poster you need to know what size you’ll need. We get a lot of jobs that come in to us from customers who want to print a big poster from an image on their mobile phones. When we try to print them they come out “fuzzy” or “blurred” and sometimes pixelated – i.e. you can see actual square pixels making up the poor image.

So what file size do I need? If you look at the picture above it neatly summarizes the problem. The image on the left is printed at 60dpi (dots per inch) whereas on the right it is printed at 300dpi (thank you urban sign & print for the image).

Your eye immediately spots the lower resolution image (60 dpi) is fuzzy and not as clear as the 300dpi image – and that’s partly due to that you are viewing it from a distance of around 0.5m.

So, having an image which is 300 pixels per inch is a general rule of thumb for printing up to A3 in size. This would mean that (as printers) we could take each of your pixels in your image file and print is as a dot on the printed page.

Now we just have to do a bit of mathematics. For an A3 poster the dimensions are 420mm x 297mm or 16.5″ x 11.7″. For us to print this at a minimum of true 300dpi we will need 4950 x 3510 pixels or about 17 megapixels which roughly equates to an image from a decent iPhone or Samsung Galaxy 12Megapixel phone camera.

However, for bigger posters or wallpapers which are intended to be viewed from a greater distance (say 2m away and further) we can reduce the image resolution to 100ppi with perfectly acceptable results.

If you want to order an A0 print (1189 x 841mm or 46.8″ x 33.1″), the image size should be 4680 pixels by 3310 pixels at 100 dpi – i.e roughly 16 Megapixels.

So as a rough guide, a good quality camera (16 Megapixels) can shoot images that can be printed 300dpi at A3 or 100dpi at A0 in size – both should be acceptable. However, older smart phones with say a 6Megapixel camera will not be able to produce a decent print when enlarged.

TOP TIP – when you design your artwork always view it on screen at 300%, and if looks fuzzy then that’s how it will print. 

General Guides for all file types

Photoshop (.psd): Make your PSD file set to at least 75 dpi at full sign size in inches. Do not compress or optimize your PSD, save at 100% quality. Output as TIFF file. 

Illustrator(.ai): Convert all text to outlines. Expand all fills and stokes. Output as EPS or PDF file. 

InDesign(.indd): Package file with all linked raster and vector files, fonts and print ready PDF included. 

JPEG & TIFF files: Make sure your image is set to at least 75 dpi at full sign size in inches. Do not compress or optimize your image, save at 100% quality.

If the image(s) you find for your project is smaller than the minimum size of 2000 x 3000 pixels, you could consider purchasing several large images to make up the size of the poster. By using several photos on your project, you could design a collage or grid pattern of images on your poster. This may also help to convey your message in a very engaging way.

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