[CREATE] [Mypaint-discuss] Resolution information in ORA

[Gez]

El vie, 28-02-2014 a las 19:14 +0100, Sebastian Wahl escribió:
>  > * Do we need an extra sentence or two in there saying that a) apps
>  > *must* populate xres and yres if they write *any* data into the ORA
> 
>  > file with non-pixel sizes, or b) that 300ppi is a Very Good Idea
> these
>  > days ? 
> Maybe we should just avoid mixing units and require the usage of pixel
> for sizes? From what I see, applications only seem to treat ppi
> information as meta-data for printing; changing ppi from 72 to 300 in
> Gimp does nothing to the font size, 18pt stays 18pt.

Congratulations, you just found a bug in GIMP :-)
When you change the resolution of the document, the type layers should
keep their appearance but the real world units should be updated.
So, for instance, if you have 40 pt type in a 300 dpi documents and you
change the resolution to 100 dpi without touching the pixel count, the
type layer should change to 120 pt.
IMO, that's a bug and should be fixed.

Regarding your suggestion of always using pixels and avoiding mixing
with real world units, keep in mind that people creating stuff for
physical outputs need to use real world units.
Imagine something as simple as printing a 10 cm. red circle in the
middle of an A4 paper without real world units. It would be a nightmare.


> What I fear is that some applications which behaves like Gimp would
> just change the resolution whenever the user changes it, without
> updating all the non-pixel based values. Then you would open it in
> another application only to find out all the sizes have been messed
> up. Defining font sizes based on ppi thus seems like the less reliable
> choice to me.

Ask inkscape users about type size in pixels. :-)
It's a PITA to convert real world units to pixels. Your tools should do
it for you, and as fas as I know, the only way to do that is having a
resolution reference.


> 72 ppi does seem like the best choice for a default. The whole dpi/ppi
> units are completely messed up anyway, often meaning different things
> in different context, sometimes used interchangeably, other times
> differentiated. If all other applications believe 72 ppi is the
> default, lets just roll with it instead of risking to cause issues
> with novel defaults.

I don't think it's messed up. Although it's true that dpi/ppi are
confusing terms when it comes to screens or printers, in the context of
raster documents dpi and ppi mean the same, and they refer to how many
pixels of that document have to be displayed in a real-world unit (in
this case in an inch) when it has to be represented in a physical
output. All the programs I know treat bitmap documents that way.

Anyway, I just wanted to point out that today, 72 dpi seems more a
legacy default than a thoughtful decision.
The only predictable outcome of using 72 dpi is that type in pixels will
have the same size than type in points on screen. But I wonder how
useful is that if we consider that a 72dpi resolution is inadequate for
good quality print.