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"Low" versus "High" Image Resolution (dpi)...
What does it mean?

pixelation example for trade show display graphics

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.

dpi example for trade show display graphicsThe 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.

For our 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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