Questions about DPI in pictures?

What causes DPI in pictures to go down when editing pics in photoshop? using filters or ';contrast';? resizing pics? if i turn up the ';contrast'; on a pic from 0 to 100, does that change the quality of the pic or DPI? how can I be sure to keep the quality of the pic in photoshop? is there a certain way to export the pic?



ANY help will be greatly appreciated! Thanks

Questions about DPI in pictures?
As the name implies it is the number of dots in 1 square inch on printer output or on a display monitor. Its often discussed as resolution. But photo resolution is better described as pixels per inch which may be different than the DPI output which could be used to describe a printers resolution. Using filters and changing contrast should not change your DPI . Resizing can change the DPI in photshop go to Image-resize image and in a box there it will tell you your DPI