# Optimal scanned resolution for final printing at 1 x 2,5 m [duplicate]

We have a piece of artwork (~21 x 30 cm) originally scanned at 300 dpi

Should we rescan it at another resolution if it is going to be printed on a poster of 1 x 2,5 m ?

• At what distance should it be recognizable (optionally, for text only, readable)? 300 dpi is plenty for books and magazines, and these are read at half a meter away, tops. Nov 15, 2014 at 16:40
• @jongware Thanks for responding. It's mostly artwork, although there's a bit of text. But I don't think people are going to look at it from very close. Is there a rule of thumb for the optimum ratio viewing distance: dpi ? Thanks in advance
– ira
Nov 15, 2014 at 17:07
• I found this to help with the viewing distance question. (premierpress.com/2013/05/resolution-recommendations) I'm not affiliated with this company however it could help you deside if you need to rescan the image. From what I calculated your image would be around 31 ppi. According to the site that I am using for reference this would be ok for a viewing distance of 25 Feet. Nov 15, 2014 at 19:26
• @Art of Fitz. Thanks a lot for your reply. People will almost certainly be looking at the image from closer than 25 feet. Two more questions, if you don't mind: (I know the first question is very naive, but better safe than sorry) As a general rule, the larger the size of the displayed image, the smaller dpi that is required ? For an image of 1 x 2.5 m is 300 dpi almost definitely overkill ? Thanks again for your help.
– ira
Nov 15, 2014 at 20:45
• This is difficult to answer a general "Yes". Some files if built correctly could be printed at a lower ppi. However, the file would need to start at the final dimensions in order to proceed. Due to your original question. Your file is at a small dimensional size. So increasing this file you are limited in how large it can increase. So maybe the rule you're looking for is "Start Big go Small." Overkill no, I know a print company that can print 10 feet by ?? long at 1,000 ppi. It depends on how much clarity you want in the final print. Nov 15, 2014 at 22:22

I dug a little deeper I really want to provide you with the most accurate answer. The Scan should be at 12000 x 29700 pixels. How did I come up with this number... Well I'll provide the math really simply and then if you really want to delve deep follow this link to All About Digital Photography.
Take your final dimentions `1m x 2.5m`
and the printer output of `300 ppi`
I then convert your `Meters` to `Inches`
1m = `39.3701`
2.5m = `98.4252`
Then you calculate the pixel dimentions
`40in * 300ppi = 12000` (I rounded up the inches)
`99in * 300ppi = 29700` (I rounded up the inches)
The scan should be at 12000 x 29700 pixels for a resolution of 300 ppi. I know this is a few days after our original comments. However, I knew that I needed to find some resources that could help me backup my math and explanation. Hope this helps.

• But note that rarely would you need to print a 2.5m poster at 300dpi. A large-format printer would likely be running at 100dpi for most uses.
– DA01
Dec 18, 2014 at 1:40