Quote:
Originally Posted by wdfifteen
True, the terms describe similar, though not identical concepts, but they are completely separate. To say "DPI ='s 2.5x's line screen" makes no sense.
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Part of the confusion is that DPI relates to the output resolution of the device. It is commonly confused with, become synonymous with and has generally replaced PPI these days.
Old timers know the difference, todays generation rarely use PPI as a term.
Because a computer generates images in pixels, a grid and printers lay down dots of varying size to trick our eye into seeing shades the image resolution becomes and issue.
4/c plates run lines at different angles to try and get a nice roseate.
When the grid is overlaid by the line we find that some pixels fall on a portion of the dot and either need to be included or dropped. When the PPI is too low, the grid too large, a lot more pixels get included giving us that pixelated, square edged look.
So we need twice the PPI for the intended line screen so we have enough pixels to lose without affecting the image quality.