could anyone please help me with this? I've created a design (for display on web and on mobile devices) and I need the pixel ratio to be let's say 500px by 500px, but the dpi to be 200dpi instead of 72dpi. The default in "Save for web" seems to be 72dpi and I can't seem to change it. At the moment, if I try to change the dpi in Illustrator or in Photoshop it automatically changes the pixel size instead of creating a higher dpi for the pixel size I need. The programmer I work with wants the pixel dimensions to remain 500x500 and the resolution to be 200dpi, how could I do that? Many thanks in advance!
dpi comes into play when printing. It stands for dots per inch. In your example, at 200 dpi and 500x500 pixels, the resulting image would print at 2.5x2.5 inches. (500/200 = 2.5)
When just saving a file (not printing) there are no physical dimension, just pixel dimensions. So dpi is not relevant without a physical dimension involved.
When we design for Web, we use 72PPI (Pixels per inch), So if you want to save a document using 200PPI settings then use Save As and don't use Save For Web
Actually when saving for web we use 200 dpi now in 2015 since retina screens process images at 200dpi
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