Date: prev next · Thread: first prev next last
2016 Archives by date, by thread · List index


On 3 Feb 2016, at 7:24 PM, SOS <sos@pmg.be> wrote:


On 3/02/2016 3:55, Kohei Yoshida wrote:
On Wed, 2016-02-03 at 10:52 +1100, Chris Sherlock wrote:
The other question is: why would we not want to the actual DPI and
screen resolution?
My understanding is that, historically, the OS provided a function to
query DPI but what gets returned from such function was not always
accurate (or always not accurate depending on who you ask).  So, the
workaround at the time was to assume that DPI is always 96 (and
hard-code that value) regardless of what the OS told you, which worked
just fine because the monitors used back in the day had the same screen
resolution.
Mostly DPI is found in the header of a pixelfile (taken by camera). Unfortunately it's not the 
photographer who gets to decide about the needed DPI.
DPI is actually a wrong definition for documents, Dots Per Inch is a definition used by output 
devices. Screens need a PIXEL par DOT but for print devices there is no precise correlation 
between the number of dots used by the device and the pixels needed in  the image for having a 
maximum image-view quality.
The print industry has come to some standards by trial and error.
- monitor screens need 96 - (220-retina) pixels per inch
- laser printers need 150 pixels per inch (up tot 2000 + dots)
- offset printers need 254 -300 pixels per inch (up to 3000 dots)

Definitely true :-) Only in OS X’s case, it doesn’t actually report back the correct resolution 
unless you ask for the backing coordinate system. 

The PPI business is a red herring I think I’ve introduced into this discussion I’m afraid. We 
calculate the PPI ourselves (and call it DPI) based on the reported pixels, and the size of the 
screen in mm (which we obviously convert to inches). 

I guess I’m curious as to what is relying on the screen resolution and PPI. 

Although… it’s funny that we have the function SalGraphics::GetResolution, but that returns the PPI!

Chris

Context


Privacy Policy | Impressum (Legal Info) | Copyright information: Unless otherwise specified, all text and images on this website are licensed under the Creative Commons Attribution-Share Alike 3.0 License. This does not include the source code of LibreOffice, which is licensed under the Mozilla Public License (MPLv2). "LibreOffice" and "The Document Foundation" are registered trademarks of their corresponding registered owners or are in actual use as trademarks in one or more countries. Their respective logos and icons are also subject to international copyright laws. Use thereof is explained in our trademark policy.