Paper: Info Sheet: Image Resolution:
DSDN144 Digital Photographcis Image Resolution
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refers to the number of pixels per unit of measure in the digital image
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expressed in pixels per inch (ppi), should not be confused with dots per inch (dpi) - which is a measurement of output resolution on a printer
If you keep increasing the size a digital photo the pixel size will continue to increase until you can see each separate pixel, resulting in an image that looks jagged and blocky
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A 457.1 Kb digital image with a resolution of 300 pixels per inch will print at 3.34cm . The pixels are too small to see.
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A 457.1 Kb digital image with a resolution of 72 pixels per inch will print at 13.93cm . The pixels will be visibly noticable.
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A 457.1 Kb digital image with a resolution of 10 pixels per inch will print at approx. 1m . The pixels will be extremely obvious.
Put in simple terms, smaller-sized prints will have smaller-sized pixels and more of them to the inch (a higher ppi count) while of the same photo larger-sized prints will have larger-sized pixels and less of them to the inch (lower ppi). Using too low a resolution for a printed image results in pixellation--output with large, coarse-looking pixels. Using too high a resolution (pixels smaller than the output device can produce) increases the file size and slows the printing of the image; furthermore, the device will be unable to reproduce the extra detail provided by the higher resolution image.
72 ppi
300ppi
Interpolation •
resamples the image by adding more pixels to it
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if you increase the dimensions in Photoshop’s Image Size dialogue box with the Resample Image box ticked your image will interpolated
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Photoshop uses a mathematical calculation to “guess” the colour of the added pixels.
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Can be done within reason but too much and your image will be noticably degraded.
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Try and avoid increasing your image more than 130% and never more than 150%.