Experience with current OS/GUI integration of PNG format

[Stefan Weisse]

Hello,

firstofall I think it is polite if I introduce myself shortly. I am
working at basic physics research and my job is to contribute to control
systems of it (particle accelerators in that case). I have devoted quite
some amount of my working time to near realtime video systems (image
acquire, LAN image transport, image display and analysis). To rework the
current (aged, dying) setup also a look was taken at PNG image format.
Because of its advantages* (having no any considerable alternative), PNG
was chosen for storing/retrieval of so-called beam spot images that will
be generated/reloaded with software working with the new, next
generation setup about to be introduced.

Currently I am creating API for physicists and engineers on top of
libpng to read/write more than just a plain PNG file. To put a long
story short: It would be helpful for the physicist to easily be able to
find out more on extra contents of the PNG file. Some already defined
text chunks like "Description" I favour to use. Built-in operating
system support to show such extra description (like list text chunks) is
necessary in order for it to work.

I have checked with Microsoft Windows XP Explorer (not Internet Explorer
to avoid misunderstanding) (right click on PNG file, image properties,
Summary, Advanced View) that the only text chunks (out of the defined
set according to the spec) that will be displayed there are "Software"
and "Copyright". Well, sounds like Microsoft ;-)

Linux/KDE 3 is much more supportive. On Konqueror right-click file
properties I can see any text chunk I have put additionally to the file
also which gives perfect overview. Unluckily, general gnome support I
did not find.

The question I have is:
Does anyone know more about PNG OS integration? Are there any magic text
chunks (or other kind of metainformation) that will be displayed
anywhere? What about Vista or Windows 7? Are there any text chunks that
can be directly seen with Gnome standard utils that come on any desktop?

My current plan is to fill "Software" chunk with something short but
descriptive, because it can be easily seen on most platforms (XP Pro,
Linux KDE 3). But this is certainly no string which an IT specialist
would suppose to find there. And only a small string value will fit
according to Windows XP Explorer file summary tab dialog limitations.

Even if you do not have more information on OS integration for me I
would also like to get feedback anyhow so feel free to comment!

regards,
Stefan Weisse
DESY
Germany

* open source
open standard
community maintained
no patent issues
fair licensing (libpng: LGPL v2)
libpng is available on many platforms
widely supported and used across the industry
natively supported in Java


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[John Bowler]

From: Stefan Weisse [mailto:stefan.weisse@...]
> Built-in operating system support to show such
>extra description (like list text chunks) is
>necessary in order for it to work.

If the constraint is that there must be pre-existing software on each target
operating system to show the extra information I think the problem can't be
solved.  What you have (the Software tag) doesn't seem to work on Windows
Vista.  I can't find a way to get the Vista version of Windows Explorer to
display *any* PNG text information!

>Linux/KDE 3 is much more supportive. On Konqueror right-click file
>properties I can see any text chunk I have put additionally to the file
>also which gives perfect overview.

I have KDE4 installed with Dolphin and the "properties" dialog is only
displaying very basic file properties - less than Vista.

I think in both cases (Windows and KDE) it may be possible to install
add-ons to enhance the property display, but it sounds like a lot of work
and it would require an installation on every machine.

I'd recommend using Qt to write a minimal preview app/directory browser that
displays the text chunks you set.  Qt is portable and the QImage class
apparently supports reading any text fields (though I have never tested
this!)

You can probably prototype something by hacking the "Image Viewer" example;
it seems commendably simple and you should just need to add another QLabel
to display the textual information.  That doesn't include the directory
browsing capability, but that can be added later.

If you do this you will have complete freedom over the tags you use and can
use the text chunk tag mechanism to appropriately name the information you
add.

John Bowler <jbowler@...>


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[Glenn Randers-Pehrson]

On Tue, Apr 28, 2009 at 11:27 AM, John Bowler <jbowler@...> wrote:
> From: Stefan Weisse [mailto:stefan.weisse@...]
>> Built-in operating system support to show such
>>extra description (like list text chunks) is
>>necessary in order for it to work.
>
> If the constraint is that there must be pre-existing software on each target
> operating system to show the extra information

Maybe you could do something with ImageMagick/GraphicsMagick which
exist or can be installed on most OS.  You could write a small GUI
that reads the output from "identify -verbose" and displays the
text-chunk data.  "pngcrush -n -v file.png" will do it too, but only
for PNG files (IM/GM will show the textual metadata from lots of
file formats).

Glenn

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[Ralph Giles-2]

On Tue, Apr 28, 2009 at 5:34 AM, Stefan Weisse <stefan.weisse@...> wrote:

> Are there any text chunks that
> can be directly seen with Gnome standard utils that come on any desktop?

Under Gnome, neither nautilus (the file manager) nor eog (the image
view) appear to display even the software tag. The tracker search
tool's indexer does read a specific set of tags, including
description, from the png_get_text, or from an XMP stanza embedded in
an iTXt. So presumedly one could at least find (the previous day's)
images by searching.

The display situation seems to be similar on MacOS X; I didn't check
if the indexer read png file metadata.

> fair licensing (libpng: LGPL v2)

The libpng license is more permissive than the LGPL, closer to a
three-clause BSD license.

 -r

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