Digital images are made up of a
bunch of different colored "pixels" (square dots). How many pixels
there are in a given area of the image is what resolution is all about. DPI
stands for dots per (linear) inch. A 72 dpi image would have 72
pixels per one linear inch, or 72x72=5,180 pixels in a square inch. When
there are enough pixels per inch so that the pattern is small and fine, the
pixels will blend together and look continuous to the naked eye. However, as
the pixel count per inch drops, the individual pixels will begin to show,
and the image will appear "pixelated" (jagged, blurry, and/or
chunky), as shown in the example pictures above and below.
size (dimensions) of the original image is just as important as the dpi. A
5"x7" image that is 300dpi is NOT the same as a 21"x27" image that is
300dpi. The 5x7 image would be 1500x2100 pixels (5x300 by 7x300).
The 21x27 image would be 6300x8100 pixels. The more important point is
that the 5x7 image may work for a brochure, but if one tried to use it as
the background of a 9 foot wide trade show display, the dpi at final size
would only be 14 dpi (1500 / 108 inches), and the resulting image would look
very badly pixelated. It is better to look at the overall pixel dimensions of an
image instead of just the dpi. One can then determine the final dpi when the
image is scaled up to final output size.
custom-printed trade show displays, we recommend that images should be about
75dpi when printed at the final full size graphics. We have found that 75dpi images look very good for trade show
display graphics, and higher resolutions are unnecessary. If you are
purchasing stock photography images for
our trade show displays or any
other displays as well, we highly recommend buying the highest resolution version of
the image, even if it costs a bit more.
Images that are
intended to cover the entire background of the trade show display can
often be a bit lower and still look good (a lot depends on what the image is
and if it has any close-up or sharp features). While we recommend using images that are
about 75dpi when they are scaled up to the final size for printing, it is only a recommendation. You
may be ok with a lower resolution image, and/or it may be the only image you
have for your trade show display design. You can judge the quality of the
images in your design by simply zooming in on them. If the image looks good
when you zoom in on it, then it should look good on your display when viewed
from a few feet away. In any event, the final call on whether your image
resolution and quality is acceptable is yours.
One final point -
the resolution of the original image is the critical factor. People
sometimes make the mistake of thinking they can take a low resolution image,
put it in Photoshop, and then change the resolution to 300dpi to make it a high
resolution image. While Photoshop can usually effectively double the
resolution of an image using interpolation, that's about the limit. Changing
a low resolution pixelated original image in Photoshop to 300dpi will just
result in a very large file size 300dpi image that is still pixelated. You need to start with a high resolution original, and you also need to create your original
Photoshop files in high resolution.
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