Understanding Monitor, Image, and Device Resolution
Remember that raster images are all about resolution. Images have a specific scanned resolution (spi, samples per inch), your monitor has a resolution (ppi, pixels per inch), and output devices such as inkjet printers (dpi, dots per inch), and high-end presses (lpi, lines per inch). While all these terms may seem a bit complicated, they're not; they simply explain how much resolution, or information is contained within the image.Most computer monitors are set to a fixed resolution of 72 or 96 ppi. Say you scan an image a 4 by 4 inch image at 288spi (that's 4 times the resolution of a 72ppi monitor). If you attempted to display the image at 100 percent view, the monitor would take the image pixels and adjust the width and height to match its resolution, so the image would be 16 by 16 inches (288 divided by 72 = 4). With monitors 16 inches is not an exact number, but it's close enough for this example. If you attempt to reduce the zoom size of the image to make it fit the monitor size, Photoshop will have to remove pixels from the image to make it fit. This typically causes the image to generate jagged lines; especially around angles lines. The moral of this story is when adjusting an image for viewing on a monitor, for example a slide presentation, never change the zoom of the image to fit the monitor, always adjust the resolution by selecting Image menu, and clicking Image Size.When it comes to output, such as to an inkjet print, the rules are a bit more forgiving. Many output devices have print resolutions of 1,440 or higher. However, we're not talking about fixed monitor pixels (ppi), we're talking about dot of ink hitting a piece of paper (dpi). Most inkjet printer, because of the dot gain of the inks (that's the amount of space a dot of ink spreads when it hits the paper), does not need image resolution greater than 300spi. Unlike a monitor, if you use higher resolutions than needed, the image typically will not suffer, quality wise, you'll just be printing an image with a larger file size. However, that can be a time-wasting problem. For example, a 300spi 8 by 10 image will have a file size of about 20MB, the same image scanned at 1200spi will produce a 329MB file size. When you print the two images, you will probably not notice any quality difference; however, it will take, on average, 6 minutes longer to print the 1200spi document on most mid-range printers.The bottom line is that resolution represents the amount of information contained within a linear inch; however, various devices handle that same resolution number differently. The good news is that understanding those differences helps you to create a useable workflow. Knowledge is power.
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Remember that raster images are all about resolution. Images have a specific scanned resolution (spi, samples per inch), your monitor has a resolution (ppi, pixels per inch), and output devices such as inkjet printers (dpi, dots per inch), and high-end presses (lpi, lines per inch). While all these terms may seem a bit complicated, they're not; they simply explain how much resolution, or information is contained within the image.Most computer monitors are set to a fixed resolution of 72 or 96 ppi. Say you scan an image a 4 by 4 inch image at 288spi (that's 4 times the resolution of a 72ppi monitor). If you attempted to display the image at 100 percent view, the monitor would take the image pixels and adjust the width and height to match its resolution, so the image would be 16 by 16 inches (288 divided by 72 = 4). With monitors 16 inches is not an exact number, but it's close enough for this example. If you attempt to reduce the zoom size of the image to make it fit the monitor size, Photoshop will have to remove pixels from the image to make it fit. This typically causes the image to generate jagged lines; especially around angles lines. The moral of this story is when adjusting an image for viewing on a monitor, for example a slide presentation, never change the zoom of the image to fit the monitor, always adjust the resolution by selecting Image menu, and clicking Image Size.When it comes to output, such as to an inkjet print, the rules are a bit more forgiving. Many output devices have print resolutions of 1,440 or higher. However, we're not talking about fixed monitor pixels (ppi), we're talking about dot of ink hitting a piece of paper (dpi). Most inkjet printer, because of the dot gain of the inks (that's the amount of space a dot of ink spreads when it hits the paper), does not need image resolution greater than 300spi. Unlike a monitor, if you use higher resolutions than needed, the image typically will not suffer, quality wise, you'll just be printing an image with a larger file size. However, that can be a time-wasting problem. For example, a 300spi 8 by 10 image will have a file size of about 20MB, the same image scanned at 1200spi will produce a 329MB file size. When you print the two images, you will probably not notice any quality difference; however, it will take, on average, 6 minutes longer to print the 1200spi document on most mid-range printers.The bottom line is that resolution represents the amount of information contained within a linear inch; however, various devices handle that same resolution number differently. The good news is that understanding those differences helps you to create a useable workflow. Knowledge is power.