[Digikam-devel] digikam PNG workflow...

[Thorsten Schnebeck]

> Yes, i know, but you forget than DNG need to have a lib about a new
> metadata format from adobe (tm) : RDF. This is not EXIF and IPTC. Actually,
> only Exif metadata are supported by digiKam.

... or xpm. IMHO xmp will be the next generation metatag standard. 
Can I embed xmp into PNG?
>
> > While its true that DNG is not an etasblished format you can make a step
> > back and look at others Adobe open formats like PostScript, TIFF or PDF.
> > All of these file formats are well known industry standards. Adaption of
> > DNG just starts (Samsung, Hasselblad) and got some positive comments also
> > from the openraw campaign.
> > If you want some samples here is a complete processed toolchain:
> > ftp://ftp.graphicsmagick.org/pub/outgoing/tiff-exif-dng/
>
> yes, but i'm not agree with openraw goal. DNG isn't the unique solution to
> make a digital negative file format. PNG can do it easily....

Hmm, I do not think so. PNG is already a demosasaic file format. So nothing 
new compared to e.g. 16bit-TIFF. DNG is a completely differend beast. It 
embeds the RAW matrix using loseless JPEG as internal compression format like 
most vendor RAW format do. If there are in future better algorithms for raw 
processing you can uses them with DNG but not with PNG. You should also embed 
the original data chunk into the DNG  These parts stay read only for ever as 
an equivalent of a real digital negative.
http://www.adobe.com/digitalimag/pdfs/dng_primer.pdf

So PNG is a full featured medium range image format but not a RAW format.

> > > - It's can be displayed without problem by all web/file managers.
> > > - It's can be decoded more speedly than RAW files (:=))).
> > > - It's a RW file format, not RAW files.
> > > - It's can be compressed like TIFF with a better ratio, and _LOSSLESS_
> > > ! - It's can be read on all computers. There are no PNG patents...
> > >
> > > Using libPNG is easy and ready to use now. I have just need to add any
> > > lines of code in png image loader to backup/extract JPEG metadata
> > > (:=)))
> >
> > All true, but can digiKam establish a PNG metadata standard?
>
> Digikam no, but PNG team yes. If tere is any PNG team member in this
> room...

The specs are there - when are specs a standard? So maybe its good to evaluate 
what other programs support extensive PNG metadata.

>
> > If I create a
> > PNG file with digiKam with an e.g. embedded ICC profile other programs do
> > not understand, it is not that good.
>
> No. there is already a standard PNG tag for ICC profile ! This is not a
> problem.

again, a spec is not a standard.

> With libPNG, you can create a new tag without compatibilty problem (this is
> the power of PNG) Using this way, you don't break compatibilty.
>
> If you want, i can create a PNG file with an EXIF tag to test (:=)))

You can use my "rawimage" too to create PNG with full metatag informations ;-) 
I was ahead of the times:
http://mail.kde.org/pipermail/digikam-devel/2005-September/001763.html
so I'm now thing about the next step :o)

> > If we use PNG simply as an extendable
> > storage container we lose compatibility.
>
> NO ! Read libpng documentation before !

Yes, I can read the specs on 
http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html
but you also know that there is one prominent plattform called "Windows" that 
has some problems with PNG on system level. And you read on some places in 
the specs that you should ignore if you don't understand a tag.

And that is what I want to say: If digiKam is the only program that uses all 
advanced PNG features its of course OK as a notable RAW-R/W alternative but I 
think is a special, a niche solution. 
  
> > As a user I would vote for a temporary PNG solution and switch over to
> > DNG when the libs are ready and handy.
>
> I a new DNG loader in the future to Digikam::DImg API, when a GPL lib will
> be availalble, or if a contributor want create this loader from strach
> using only DNG spec. personnally, i have no time to do it...

PNG is the best option we have today - but it has not a long future. Its in 
the best KDE traditions to use the tools and libs that work today.

And it would be a great feature if digiKams download window has an option to 
transform every known filetype to PNG on the fly. 


Bye

  Thorsten