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How Large Can a Photo Be Blown Up for Display Graphics Printing?
originally published in
Trade Show Buzz
by Rick Hendershot, Reprinted from the
FAQ at Canada Display
Graphics
When dealing with "old fashioned" prints or slides, images can be enlarged at
two different stages: the scanning stage, and the printing stage. At the
scanning stage, you can build greater "resolution" into the image file by
scanning it at a higher ppi rate. This allows you greater flexibility when
placing the image file in your document.
Enlarging it at the printing stage just takes the built-in resolution and
spreads it over a larger surface -- giving a fuzzier printed result. So it is
important to have sufficient resolution in the image file. Spreading the image
over a larger surface is acceptable if the image file contains sufficient
resolution to let you do this. What is "sufficient" resolution will vary with
the printing device, the printing media, and the final application. See below
for some idea of how this applies to large format display graphics.
While there are no theoretical limitations to how large a photo can be enlarged,
there are two very important practical limitations. First, the more a photo is
enlarged, the less "sharp" it is (especially when it is enlarged at the printing
stage.)
Second, the more an image is enlarged at the scanning stage, the larger the
files become. This can be very significant for large images, because if you
build too much resolution into a very large image file, the file may be too
large to transport (either on a disk or via the internet.) So the best solution
is to find the "point of adequate resolution". This is the point at which
greater resolution does not result in significantly improved image quality.
Point of Adequate Resolution for Display Graphics
We find that an image scanned at 300 ppi and incorporated into a normal letter
size page (8.5" x 11") can be enlarged at the printing stage (display printing)
up to 4 times (or 400%). That gives you an effective resolution of 75 ppi.
So, for example, say you take a 4 x 5 print and scan it at 200% to give you an
image that is 8" x 10" at 300 ppi - 2400 x 3000 pixels. This file (CMYK) will be
approximately 28 mb. If you sent this image to one of our display printers at
400% you would get output that is 32" x 40", and the quality of the printed
image would be perfectly satisfactory (depending, of course, on the quality of
the original photograph, and the quality of the scan.)
Often an effective resolution of 50 ppi is adequate for display graphics. So the
above example could be enlarged even more. This is because display graphics
images are usually viewed from a distance of more than 10 feet.
Enlarging Digital Images
All of the above applies to digital images. Generally speaking, the more
resolution you build into your original camera shot, the more detail you will
capture, and therefore the more it can be enlarged when printed.
As with a photo print or slide, once the image is shot, you cannot add detail by
just "sampling it up" -- by increasing its resolution with software like
Photoshop. Doing this will just give you a larger file with no increase in
detail.
So it is important to build sufficient resolution into your original shot. When
calculating this, work backwards from the intended final image size. For
instance, if you need an image that is 36" x 48" at 50ppi, that means your final
placed image will be 1800 x 2400 pixels.
This is the minimum resolution setting you should use when shooting your
image. It should actually be higher than this, since you will almost always be
cropping your image. Not all digital cameras explain resolutions in these terms,
so you will have to experiment with your camera to find which settings give you
the appropriate resolution.
If the resulting files seem surprisingly large to you, remember that you are
dealing with very large printed images, and assumptions that apply to 4 x 5
prints or images printed in brochures or magazine ads generally do not apply to
display graphics.
For more information go to dig deeper into our website or go to TradeShow-Display-Experts.com
for more ideas.
For more articles see the
Linknet Trade Show Library.
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