Translate feet/inches to resolution?

d12dozr

I am producing a render that will be used on a 10' x 15' outdoor sign. I've looked at DPI and "for print vs. for web" until my eyes cross, but I don't understand how to calculate the render resolution size in pixels.

What DPI or pixels/inch would I need for a large outdoor sign? How would a sign resolution DPI compare to printing on letter paper?

dedmin

It depends on the viewing distance - for a poster like this multiply each size by 300 - 300px per inch.
3000x4500px

honoluludesktop

Perhaps the best place to get your question answered is at a print shop that specializes in large outdoor signs. Determine how far the average distance that the sign will be viewed from, and ask them your question. My computer display outputs at 96dpi. Depending on how far a viewer is away from the sign, the necessary dpi of your render will vary. at 96dpi, a ten foot sign is 10'X12"X96 pixels. But, if the viewer is further back then the distance you look at your display, the pixel count can be lower.

Don't confuse printing dpi with render dip, a render output at 96 dpi can still be printed at 300-1200 dpi, however with no better resolution then at 96 dpi.

d12dozr

@dedmin said:

...for a poster like this multiply each size by 300...

Thanks dedmin, but I'm kinda thick, and need a little more explanation please.
So you multiplied 10 feet by 300 for 3000px and 15 feet by 300 for 4500px...so far so good.
Then you say...

@unknownuser said:

300px per inch.

...and I get lost. where does that 300px/inch come from if you multiplied 10 feet?

honoluludesktop, thanks for your suggestion. I have emailed a local print shop for help as well.

notareal

Here is a good explanation about dpi:
http://www.andrewdaceyphotography.com/articles/dpi/
And after understanding dpi, you can figure needed image resolution in pixels based on needed quality for different distances:
http://www.kerkythea.net/phpBB2/viewtopic.php?p=68702#68702

thomthom

Another one about DPI: http://www.rideau-info.com/photos/mythdpi.html

Gaieus

10'=120". At 300 dpi (read "dot per inch") it is 120x300=36,000 pixels. This is only required for fine prints in nice looking books.

For outdoor boards, this would be a waste and luxury. Generally speaking you would look at such a bog board from around 10', too, so about one third would be fairly enough. Say 12,000 pixels or even a bit less. So your output image should be around 18,000x12,000 pixels which is still rather big for a SU export but if you are on a 64 bit system with lots of RAM and using some studio renderer, it should be just a matter of time.

sketch3d.de

you may use this for calculating stuff.

hth,
Norbert

brodie

I'd go with Gaieus' advice. You absolutely don't want to go with 300 PPI for a sign that large. 300 PPI is a good goal for stuff you'll be looking at from 8 inches away but is total overkill for your purposes. I've heard of billboards being printed with as low as 10 PPI.

You could do a test by printing printing out a small part of your image on, say, an 11x17 page. I will probably look pretty pixelated, but then if you tack it to the wall and stand as far away as people will typically see the full print (10' or so) it'll give you a good idea of how the full print will look. If you still notice pixelation, then you'll have to use a higher resolution.

-Brodie

d12dozr

@notareal said:

And after understanding dpi, you can figure needed image resolution in pixels based on needed quality for different distances:
http://www.kerkythea.net/phpBB2/viewtopic.php?p=68702#68702

This link was very helpful...thanks, notareal! Rafa's explanation and graphs show the ideal DPI at a viewing distance of 3 meters(which is probably what the average viewing distance will be) to be 50 dpi...this is similar what I have seen now when searching -- billboards can be 36PPI or even 10PPI as Brodie says.

Thanks to all who answered, Gaieus' explanation especially made it simple to understand

If I find out more relevant info, I will post back here.