On 2009/08/11 16:10 (GMT+1000) Alan Gresley composed: > Very interesting discussion in which I am learning much. What you say > above got me thinking and I have decided to do a test case.
> <http://css-class.com/test/css/box/pixels-points-dpi.htm> > This is what I note: > 1. The 96px and 72pt boxes are the same size with a 96 DPI setting for > the monitor. > 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. > 3. When the DPI setting is changed to 120 DPI, the boxes using pts > become 125% of their size at 96 DPI. > 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. > On the same test case are screenshots using both 96 DPI and 120 DPI. > My question to you is why a box of 100px equals a inch measured by a > ruler and not what I expected 96px? You flunked the part of the thread about desktop DPI and actual display DPI in most cases being different. :-) Only when the DPI applied to the desktop matches the DPI of the display will the measured size of a screen object in pt, mm or inches be accurate. In your case, the actual DPI of the display does not match the desktop's assumption, and is exactly or is very close to 100. Examples of this match to 100 can be seen in the http://fm.no-ip.com/auth/dpi.xhtml chart for 1600x1200 on 20", 1440x900 on 17", 1280x800 on 15", 1680x1050 on 20" and 1280x960 on 16". > 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 A applied DPI change does affect sizes in pt (which is used for chrome sizing in all modern desktop environments), mm or in, but not those in px. As DPI increases, the quantity of px required to achieve any certain physical size increases. This is why images rendered at their intrinsic size at higher DPI are physically smaller than at lower DPI, and why users of high resolution displays who are unfamiliar with zoom and forcing a minimum text size complain about too small fonts when authors declare things like body {font-size: 12px}. Viewport behavior and chrome behavior don't always follow each other, and sometimes a browser (e.g. Safari on Windows) ignores the desktop's assumed DPI setting. IOW, it's possible for e.g. 10pt chrome/menu text and 10pt text within the viewport to be different in size due to different DPI being applied to each. If on Windows you set desktop DPI to 120, Safari's chrome/menu text will be smaller than that of IE and Firefox. It used to be that in Firefox a DPI override in about:config's layout.css.dpi would apply to both the viewport and the chrome, but for over a year now (all of the 3.x varieties IIRC) its chrome obeys the desktop setting regardless of the about:config layout.css.dpi setting. -- How much better to get wisdom than gold, to choose understanding rather than silver. Proverbs 16:16 NKJV Team OS/2 ** Reg. Linux User #211409 Felix Miata *** http://fm.no-ip.com/ ______________________________________________________________________ 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/
