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Paper: Info Sheet: Image Resolution:

DSDN144 Digital Photographcis Image Resolution


refers to the number of pixels per unit of measure in the digital image


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


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.


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.


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


Interpolation •

resamples the image by adding more pixels to it

if you increase the dimensions in Photoshop’s Image Size dialogue box with the Resample Image box ticked your image will interpolated

Photoshop uses a mathematical calculation to “guess” the colour of the added pixels.

Can be done within reason but too much and your image will be noticably degraded.

Try and avoid increasing your image more than 130% and never more than 150%.

Week6 - Resolution  

Image resolution and DPI

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