Hi Luca, I'm starting to understand better now. Thank you for taking the time and effort to explain. From your previous message, now I'm down to this place, where I'm stuck: "Here is the point: ...... Example: an A4 is 210 mm x 297 mm. Let's convert it in px using the 90 DPI convention: 210/25,4*90 = 744 px 297/25,4*90 = 1052 px " I think it uses math symbols that I don't understand. (I've learned math with that ancient world of inches, feet and yards, rather than metric system.)
Is it 210 divided by 25? If it is, why do you divide by 25?
I think 4* 90 means 4 times 90, but I don't understand where the 4 comes from. And the comma is foreign to me, if it means anything more than pause.
Thanks again, brynn
-----Original Message----- From: LucaDC Sent: Monday, February 06, 2017 5:01 AM To: inkscape-devel@lists.sourceforge.net Subject: Re: [Inkscape-devel] UX help
Hi Brynn, first of all thank you for reading and trying to understand what I've written.
I've gone straight over some concepts that would deserve a closer examination. My intent was to be as easy as possible.
In our context 1 px = 1/DPI inches. This is because when referring to "px" we mean the SVG Working Group (very unfortunate, IMHO) definition of it. It was 1/90 inches recommended and now has been changed to 1/96 inches mandatory. Moreover, in our context "px" is referred also as "user unit". In latest releases of Inkscape you can define your own user unit with regards to physical dimensions, thanks to the use of the viewbox attribute and the new internal Inkscape generated files conventions.
Your point about "real" pixels is correct: 1 pixel is a fixed size _for_each_particular_screen_ (better say: for each particular medium). This means that 1 pixel is not an absolute unit because its dimensions (plural, because there are devices on which pixels are not even square) depend on the particular device you're referring to. There's not such a possible universal fixed conversion as 1 pixel = xxx mm or 1 px = yyy inches. To link pixels and absolute physical units we need to speak about PPI, that is pixels (points) per inch. So, 1 pixel = 1/PPI inches = 25,4/PPI mm. Each real device has its PPI ratio. But, as I see, this math is exactly the same as 1 dot = 1/DPI inches = 25,4/DPI mm. This has led to interchangeable use of PPI and DPI, even if they aim to express different concepts.
In any case, resolution only matters if you need to convert between different physical mediums that each have its discrete resolution. Inkscape is a vectorial drawing program so it could not care about the resolution but only about dimensions (in whatever unit you need). So, why should I (who always draw in mm) care?
This is Inkscape's fault that chose to enforce the misunderstood claim on defining px as physical unit, using px as the only unit in which to save its files; that is converting all real physical units (like mm, inches and so on) into px @ 90 DPI. This choice has been eventually proven to be unwise when the same SVG Working Group decided to change their own "physical px" definition from 90 DPI to 96 DPI, just showing that it's not a physical unit at all (try changing 1 mm definition at your pleasure, if you can...). Fortunately in the meantime Inkscape has gained the ability of saving files in other units than px, so now you can have an entirely mm or entirely inches document if you whish so. Now only old "px @90 DPI" documents have problems because they need a conversion.
One important still missing feature in Inkscape is the ability to define a document's specific DPI ratio. This would even solve all problems with old documents. And would finally let people create, for example, a real 300 DPI document (a document in px where 1 px corresponds to 1/300 inches) in which to draw shapes using mm and inches without having to make on the fly numeric conversions (that is if you draw a 2 inches line it will be 600 pixels long).
All this is my (surely poor, hope not too wrong) understanding on the subject.
Luca
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