They surprisingly read it, almost all of them, or at least all the basic software of the OS from which people open the image and can quickly look at it. PNG is an underrated format, is not well received from print companies, but things started to change since is what you get by default from web applications, and the only lossless.
They do convert in the nearest dpi value, even if the tag sets to some integer in dot per meter and then it becomes 299.9923 dot per inch. They will just print at 300.
Regarding the specs, no one will support the non square pixels that i know of, and by default you will always find 1, also no one will easily support different resolution per axis.
I did not follow the thread, are we missing png dpi support in inkscape?
Il giorno gio 20 set 2018 alle ore 08:20 C R <cajhne@...400...> ha scritto:
Nice! Excellent information.
So does Inkscape ever set a value for these or is it always 0 (unknown unit?)
Not that it really matters all that much... Any print company worth anything will know that a raster file of pixel dimensions 2480 pixels x 3508 pixels is A4 @ 300dpi (no bleed)
Yes, I've encountered printers who didn't, but it's pretty basic stuff, so I tend to avoid companies that can't get DPI right. :)
It's generally advisable to send a pdf, which includes the relevant size information, since it properly stores all that stuff, but imho, there's nothing wrong with popping out a png at the proper pixel dimensions and saying "I'd like this printed at A4 300 DPI". That should be more than enough information for any printer to get it the right size.
It's been on my to-do list for a while to make a video on DPI. It's quite astonishing how many designers (and printers) just don't understand it.
Thanks for the info. It would be a good idea to make use of the png unit specifier, however I don't know how many pieces of software will read the value and use it, even if we include it.
-C
On Thu, Sep 20, 2018 at 1:36 AM ian_bruce--- via Inkscape-devel < inkscape-devel@lists.sourceforge.net> wrote:
On Wed, 19 Sep 2018 21:44:56 +0200 Andrea Bogazzi <andreabogazzi79@...400...> wrote:
Just wanted to add the maybe non usefull information, but nice to know, that pngs are weirdly in DOT per METER. I think they are the only graphic format to do so.
Being the conversion between meter and inch not an integer, you cannot have either 96 or 300 or 600dpi, but some float number in the nearby.
Here's the relevant part of the actual PNG specification, in case somebody wants to quote it to the fool with 30 years experience ("Dunning-Kruger effect", haha).
https://www.w3.org/TR/PNG/#11pHYs
The pHYs chunk specifies the intended pixel size or aspect ratio for display of the image. It contains: Pixels per unit, X axis 4 bytes (PNG unsigned integer) Pixels per unit, Y axis 4 bytes (PNG unsigned integer) Unit specifier 1 byte The following values are defined for the unit specifier: 0 unit is unknown 1 unit is the metre When the unit specifier is 0, the pHYs chunk defines pixel aspect ratio only; the actual size of the pixels remains unspecified. If the pHYs chunk is not present, pixels are assumed to be square, and the physical size of each pixel is unspecified.There's obviously nothing that stops you from assuming that the "unknown" unit is actually inches, or anything else, and setting the pixels/unit values accordingly.
Maybe the Inkscape interface could be adjusted to allow the PNG output resolution to be specified in dots/cm as well as dots/inch, and set the unit specifier to 1 or 0, accordingly.
Inkscape-devel mailing list Inkscape-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/inkscape-devel
Inkscape-devel mailing list Inkscape-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/inkscape-devel