jiho <jo.irisson@...125...> writes:

I have a small question regarding that: usually this one-to-one correspondance is for 72ppi (ie. the screen resolution). my screen resolution is indeed detected as 72 by the gimp. why is this different in Inkscape?

Screen resolution is your monitor's width in inches divided by your desktop resolution (the width of course) in pixels. Since people use all sorts of monitors and all sorts of desktop resolutions, the resolution is diferent for each and every user. the screen resolution is traditionally defined as 72 pixels per inch, but this value is not really representative of anything anymore - not even of the statistical average today (it may have been in the past).

Also, note that the operating system can't really tell your resolution: the monitor doesn't tell the system what size it is. In windows XP, normal resolution is defined as 96 DPI, but again, this number is meaningless.

I just measured my own monitor - it's 19" (14.75" width) LCD with a 1280X1024 resolution, and got a resolution of about 87 PPI. So I guess for me at least the number is close enough.

On Monday 12 February 2007 13:44, Jeffrey Brent McBeth wrote:

On Mon, Feb 12, 2007 at 06:36:09PM +0000, Michael Grosberg wrote:

...

Also, note that the operating system can't really tell your resolution: the monitor doesn't tell the system what size it is. In windows XP, normal resolution is defined as 96 DPI, but again, this number is meaningless.

Just to clean this up, it can and does. It is part of the DDC connection that modern monitors have with the OS. If the OS is willing to listen, the monitor can tell it its make, model, horizontal and vertical refresh rates, physical size, color depth, aspect ratio, orientation (for screens that can pivot). 87PPI sounds right, and as I have 19" monitors with 1280x1024, Linux's DDC support is currently reporting an 87 PPI (xdpyinfo will let you know what it is)

xpdyinfo agrees with Gimp, 75dpi on my Sony. Or one can always cheat and look in the manual :<)

On Feb 12, 2007, at 10:51 AM, jiho wrote:

OK, thanks for this detailed and very clear answer. so 72ppi is a kind of legacy in fact? and then 90ppi is just an arbitrary choice which reflects more today's hardware? (arbitrary is ok for me, it's just nice to understand things completely)

72 DPI is legacy from when Mac's and such brought in desktop publishing and replaced the traditional 72.27 DPI for points.

90 DPI is the recommended reference case for the "px" unit that is specified in the CSS spec. The SVG spec in turn calls out the CSS spec and it's "px" units.

So the 90 DPI base assumption is in compliance with SVG. Getting a value from the actual display would also be in compliance, but does take quite a bit more work and provides quite a few more problems.

On 2/13/07, Jasper van de Gronde <th.v.d.gronde@...226...> wrote:

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The current setting in the dialog is ignored, but the export hints on objects are honored. So if you exported some of the objects previously with some resolutions, they will be remembered and reexported with the same resolitions. Otherwise, 90 dpi is used (1 px unit = 1 pixel in PNG).

Is this reflected in the interface anywhere? In any case, I think it would make sense to do something like disable the DPI box

Yes. When you click batch export checkbox, all the rest of the dialog is disabled, except for the Export button :)

or show the average) if export hints are present and let the user enter a DPI otherwise (as well as letting the user override the export hints by filling in a specific DPI). Similar to how mixed values (for opacity or stroke width for example) within a selection are handled.

Yes, it would be nice to have the ability to override dpi and the export directory for batch export. Patches welcome :)