[digiKam-users] Thumbnails are in Progessive Graphics File (PGF)

Gilles Caulier caulier.gilles at gmail.com
Thu Apr 11 01:39:53 BST 2019

PGF is not an esoteric image compression format. It's an open source
compressor, working with wavelets.  In opposite that you said, the file
size is very optimized compared to JPEG and especially PNG. The image
quality is so far better than JPEG, and is very fast.

To store thumbnail in database we need quality and size optimization, else
we will explose the storage.

similar compression format are :

- JPEG 2000 : slow to compress/decompress (require float computation), not
fully open source (patents).
- JPEG-XR : Microsoft, patents, not open source.
- Webp : Google, opensource, but not yet finalized when we needs to choice
the DB thumbs storage..
- Heif : Apple, patents, partially open source through Nokia, very recent.

Web technology, use archaic image compression algorithm as JPEG. PNG
compression is zip like... Wevelets compression is the future, better,

So before to judge the choice done about thumbnail store in digiKam
database, take in consideration all technical levels. Thumbnails database
storage is not designed for the Web.

PGF format have been selected in 2008 if i remember.

So you need a converter. PHP use ImageMagick in background, it's the best
place to have the codec for the Web.


Gilles Caulier

Le mer. 10 avr. 2019 à 23:08, Tac Tacelosky <tacman at gmail.com> a écrit :

> Not piwigo, but DigiKam.  But since digiKam is a desktop app, it's
> normally completely self-contained.  But the discussion was about accessing
> the MySQL database in digiKam so that it could be usable on the web.  And
> that's where having an esoteric format is problematic.  If the thumbnails
> were stored in PNG or JPEG, it would literally be a few lines of code to
> render them in the web browser.
> Tac
> On Wed, Apr 10, 2019 at 3:11 PM Gerhard Hoogterp <gerhard at frappe.xs4all.nl>
> wrote:
>> On woensdag 10 april 2019 20:35:58 CEST Tac Tacelosky wrote:
>> > After digging around a bit, I think I have the answer to the question
>> about
>> > how the thumbnails are stored, which is PGF:
>> >
>> > https://en.wikipedia.org/wiki/Progressive_Graphics_File
>> >
>> > Unfortunately, I cannot for the life of me find something in PHP that
>> will
>> > convert from PGF to JPEG or PNG.
>> Probably a stupid question, but... if piwigo stores its thumbnails in a
>> database in a format that nobody uses, including browsers AND I see
>> online the
>> thumbnails being jpg, which makes sense since otherwise they would be
>> useless,
>> wouldn't that mean that in the piwigo code somewhere there's a conversion?
>> And as I see this code on github it should be there somewhere?
>> Not a piwigo user or anything, just wondering?
>> --
>> https://gerhardhoogterp.nl/latest
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