[digiKam-users] How to rebuild RAW thumbnails?

Gilles Caulier caulier.gilles at gmail.com
Sat Sep 29 09:59:06 BST 2018


Changing the color space in camera while shooting will affect preview
included in RAW.

RAW preview are mostly a small JPEG image embedded in RAW container. DK
extract this JPEG as well to render icon view thumbnails. It's very very
fast as no post processing is required.

Using RAW image data will be really slower to render large albums, and will
decrease DK performances. Even if libraw decoder can use fast RAW
extraction method without to much post processing, the democaising of bayer
matrix will be a bottleneck.

Using sidecar can be a solution. Here i don't talk about XMP sidecar file,
but the .thm file coming with RAW file (Canon generate this kind of file,
as i know)...

But this will introduce another dysfunction, as THM file include also
metadata which do not correspond well with RAW metadata (incomplete).
THM cannot be used as metadata source, and this will increase the
complexity of metadata workflow.

Gilles Caulier

2018-09-29 9:12 GMT+02:00 Andrew Goodbody <ajg02 at elfringham.co.uk>:

> On 29/09/18 07:55, Maik Qualmann wrote:
>> I did not understand the problem at first, but I can reproduce it with my
>> Nikon. First of all, it is not a good idea to take a image in B&W
>> digitally.
>> There are many more ways to do it later, but for the JPEG the color
>> information is lost. There is currently no option in digiKam to specify
>> that a
>> thumbnail should be created from the RAW image. It uses the "fastest"
>> source
>> and that is the preview image. That was of course stored by the camera in
>> B&W.
>> Maik
> Sounds like this could be a wishlist item for a 'sidecar-jpeg' which could
> be used for raw files to contain a preview image developed using the
> current edit settings for the raw file.
> Andrew
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