[digiKam-users] preferred format iOS pictures heic or png

[Gilles Caulier]

Hi and sorry for the delay...

Le mer. 20 janv. 2021 à 14:16, LCK AankopenEnRegistraties
<aankopenregistraties at icloud.com> a écrit :
>
> Hi, a newbie here so sorry for any lack of understanding about typical digiKam-users habits.
>
> I want to extract/export all pictures (10.000 in original formats mostly NEF, the others JPEG, HEIC) held in MacOS Photos, using EXIF (so no sidecars holding XMPs) as result. And then import those in digiKam.
>
> The digiKam manual (2017 version) tells me the best format to manage pictures is PNG.
>
> In MacOS Photo’s export facilities there are two options:
> 1. "Export the original picture" (generally advised; the result in my case are the NEF, JPEG and HEIC formats). A specific (iPhone HEIC-formatted) picture I selected has a size of 2,4MB.

It's normal, as HEIF compresses image using a modern algorithm,
typically based on HEVC (H265).

> 2. "Export the picture" (if modified the modified one), where the format PNG can be selected from the listed JPEG, TIFF and PNG. The same HEIC-picture as above saved in PNG format has a resulting size of 14,7MB.

yes PNG use lossless compression (old Adobe deflat) and data size is
heavy, but without to lose quality.

Alternative is to use TIFF which will give the same result as PNG.

>
> The HEIC-format has ‘better’ compression characteristics than previous issued formats, including PNG, I understand. I have read (digiKam website) that digiKam can handle Apple’s HEIC-format. But the difference with the PNG in size is staggering (to me). Will I loose anything if I choose HEIC?

yes, if compression is not lossless. HEIF can compress also loss less,
but in this case, the file size become more heavy (as expected).

This is why, for transfert or archiving, it's better to use a native
and older format which compress lossless. Later after to modify your
photo, you can export to lossy format, as JPEG or HEIF.

>
> Questions:
> A) concerning all the NEF-formatted pictures I have, should I use NEF(RAW), HEIC or PNG as targeted format (in digiKam)?
>Or should I leave the format as it originally was and leave it to digiKam to manage these different formats every time I open a picture?

NEF is very well supported but it's a read only format. digiKAm can
support its own versioning, but it cannot import versioning from
proprietary applications.

If you use XMPP sidecar, in parallel of NEF, well extra metadata that
you append to NEF as tags, rating, etc, can be imported to digiKam
without problem.

This is why we recommend to use XMP sidecar with Raw file format, to
improve interoperability.

> B) if I take pictures with an iPhone, what should I do in terms of required format in digiKam? Change to PNG or leave it as it was, meaning the HEIC format?

You can use HEIF as well and import to digiKam.

Note: HEIF support in digiKam is not perfect as :

- writing metadata on the fly is not yet supported by libexiv2 engine
used by digiKam in the background. It's planned from Exiv2 team, there
are plenty of reports about this topic from this project.
But at least for the moment, metadata can be written to HEIF file when
images are reencoded.
So with HEIF, we also recommend to use an XMP sidecar, until this
situation will be improved.

- images sequence (aka small video embedded by iphone) is not yet
supported by libheif engine used by digiKam.

- decoding HEIF is slow as libheif is currently embedded in digiKam
source code. We plan to use a system based version when libheif will
provide a better integration with cmake cross-platform framework. It's
partially done now, so it's must be a question of time...

- encoding HEIF is delegate to libx265 engine from host system and
depending of how the library is compiled, some hardware optimizations
can be disabled (as it's can be relevant of patented algorithms)

As you can see, HEIF support is not yet perfect, and this will take
time to have a mature support. This is always the case in open source
projects which want to support with patented technologies such as
HEIF.

But HEIF is the future and it's more and more used everywhere. So...

Best regards

Gilles Caulier