Setting up correct ratio for large format printing

[inquestflash]

Hello Forum,

I'm trying to understand the printing world, since my background is all about the web. So excuse me if this question is answered a million times. 

I have a few critical questions which will help me get good information from this community as always.

A) Are the large printing format banners the ones we see as posters, commercial ads on billboards usually scaled to 1/4 of their actual size in a photoshop document and then the printer sets in the machine the final output size to scale? (The obvious answer I assume would be, that any PC/MAC would struggle having a document beyond reasonable scale and with 300DPI, although scouting the web, for images if not at close range I see people saying even 90 or 150 DPI would work as DPI in the PS settings since people wont be seeing them from close up.

B) This was my approach for example the actual commercial banner is 10 metres x 4 metres (10000mm x 4000mm). 

So I made a canvas size 1/4 of the size, 300DPI of what the actual final print size will be from the print machine, once sent to the print shop.

I downloaded an image which is 300DPI with enough pixels in a photo ( athough I have seen 300DPI photos and images but with barely enough pixels)

And then placed the image within the canvas which is 1000mm x 400mm. So then I can save as TIFF or PDF, or what ever file the print shop will need to enlarge this image ready for print.

So is that the correct approach?

[gener7]

The aspect ratio is fine, but if you will be using metric:

You should set your units from Pixels to MM  118.11p/cm = 300 ppi

[inquestflash]

Thank you for pointing that out, I mustve not paid attention to the units, I'm a web guy so I'm use to pixels.

[JJMack]

Why do you have an obsession with 300ppi.  Large print size images do not have to be printed with high resolution size pixels. They will not be viewed from a distances that the human eye can resolve down to 300 ppi.

[inquestflash]

Hi JJmack

I guess because its the stanstard when it comes to anything which is for print. I remember in my college it was always 300 DPI & CMYK, so I guess it's more following the theory of what my lectures always told us. But we never did anything for Billboard banners and large scale print, that's why I needed some insight what is a good direction to take.

Kind regards.

[D Fosse]

Any good quality image will work for anything, whatever the physical print size, because it will be seen from much farther away.

You don't need 300 ppi! That's for books/magazines held right up to your nose.

A billboard can be 10 ppi and look magnificent.

[inquestflash]

Yes, you're correct, the farther away the image,  the resolution can be dropped as you said to a minimum, and also taking into consideration people drive very quickly by billboard banners, which they only view for a few seconds. So no one can spot and quality deterioration if its printed in low resolution.

Kind regards.

[D Fosse]

people drive very quickly by billboard banners, which they only view for a few seconds. So no one can spot and quality deterioration if its printed in low resolution.

That's not the point. There won't be any quality degradation. It's not that resolution can be dropped; it should be dropped because anything more is a waste of resources for no use.

In some very special cases where you can walk right up to the print, you can make a case for higher resolution. That still doesn't mean people will walk right up to it. It's physically uncomfortable. The eye wants to take in the whole, so you step back.

But even in those cases, 70-80 ppi is plenty enough. Think about it: that's around the resolution of a traditional monitor. You don't see any pixels unless you bring a magnifying glass. It's still sharp.

In fact, the 300 ppi spec for book and magazine print is much more a technical one than an optical one. It's a theoretical upper limit, above which no improvement is possible, given a standard 150 lpi screen frequency.

What it boils down to: the same image will work equally well for any purpose. Same number of pixels.

[gener7]

If I understand correctly, 1000mm x 400mm will be scaled to 10m x 4m (10x) final print size diluting that 300 ppi resolution to 30 ppi.