On Tue, Aug 11, 2009 at 04:10:45PM +1000, Alan Gresley wrote: > 2. The 100px and 75pt boxes are the same size with a 96 DPI setting on a > monitor but also they are exactly 1 inch (using a ruler) in height and > width.
...which means that, within the limits of the accuracy of your ruler, your monitor is actually displaying at 100DPI, regardless of your operating system's DPI setting. > 3. When the DPI setting is changed to 120 DPI, the boxes using pts > become 125% of their size at 96 DPI. Correct. Always remember that monitors operate purely in pixels and cannot display based on any other unit or size. The monitor's physical DPI is purely a function of the screen's physical size and the active display resolution (e.g., 1024x786, 800x600, etc.). The DPI setting in your operating system is a pretend value, as in "the operating system will pretend your monitor is 96DPI or 120DPI, since it doesn't know the actual physical DPI", which is used to convert physical measurements (such as inches or points) into pixels so that the monitor can display them. When you change the DPI setting, the ratio used for that conversion changes, so 75pt or 1" will be translated into a different number of pixels. > 4. The boxes using pixels are the same size and the box of 100px at > either 96 or 120 DPI still equals exactly 1 inch (using a ruler) in > height and width. Yep. 100px is already in pixels, so it can be displayed directly without having to use the DPI setting to convert its size into pixels first. > My question to you is why a box of 100px equals a inch measured by a > ruler and not what I expected 96px? Because your monitor isn't actually 96DPI. > BTW, I thought the higher DPI setting would make the text smaller. I now > discover the reverse is true where the text and chrome of the browser is > larger. At 96DPI, the operating system converts a 1" line into 96 pixels. At 120DPI, the operating system converts a 1" line into 120 pixels. The actual pixels on the screen are the same size regardless - remember that their size is purely a factor of the physical screen size and the active display resolution, not of the DPI setting - so the (supposedly) 1" line becomes 24 pixels longer when you change from 96DPI to 120DPI. (And note that 24 is 25% of 96, matching the 25% size increase that you noted in your 3rd observation.) -- Dave Sherohman ______________________________________________________________________ css-discuss [cs...@lists.css-discuss.org] http://www.css-discuss.org/mailman/listinfo/css-d List wiki/FAQ -- http://css-discuss.incutio.com/ List policies -- http://css-discuss.org/policies.html Supported by evolt.org -- http://www.evolt.org/help_support_evolt/
