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Spots, dots and pixels just what are dpi and ppi? - part 3 of 1 2 3 4 5

by Mike McNamee Published 01/06/2011

The top set shows an idealised model with square pixels from eight cartridges, providing 16 squares in a 4x4 array which mashes up to a mid grey, or with a change of the colours a bit of a flesh tone. The bottom set is more realistic with different sized dots, randomly placed in the square pixel, some overlapping some not. The reality is a mix of variable sizes of spots, randomly dithered around the nominally square pixel area to create very smooth tones at normal viewing distances.

Surprisingly little is the answer, providing all you wish to do is identify the model! The image to the right shows model, Charlie Edwards, scaled at 9, 18, 36, 72, 144 then 288ppi. For the image above the same images have been up-scaled without any smoothing of the pixels, using nearest-neighbour interpolation. Note the progressive improvement in the rendering of the hair as the resolution rises. If you screw your eyes up even the 9ppi image is recognisable as Charlie but this does not provide anywhere near enough information for detailed printing.

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1st Published 01/06/2011
last update 21/07/2022 08:46:23

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