Out of curiosity: digiKam is a very fast viewer for RAWs. How?

[Andreas Borutta]

Hi,

I like it a lot, that a user can scroll in-between the views of his
RAWs in digiKam very fast.

Out of curiosity and because I couldn't find infos in the handbook
about that feature:
How did you realized such a fast viewing for such big files?
Just the concept, technical details are not important.

I looked into the albums and into the directory
".kde/share/apps/digikam" but I did not find any cache.

Andreas
--
http://borumat.de

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[Dotan Cohen]

2008/5/11 Andreas Borutta <[hidden email]>:

> Hi,
>
> I like it a lot, that a user can scroll in-between the views of his
> RAWs in digiKam very fast.
>
> Out of curiosity and because I couldn't find infos in the handbook
> about that feature:
> How did you realized such a fast viewing for such big files?
> Just the concept, technical details are not important.
>
> I looked into the albums and into the directory
> ".kde/share/apps/digikam" but I did not find any cache.
>

The thumbnails are here:
~/.thumbnails

Dotan Cohen

http://what-is-what.com
http://gibberish.co.il
א-ב-ג-ד-ה-ו-ז-ח-ט-י-ך-כ-ל-ם-מ-ן-נ-ס-ע-ף-פ-ץ-צ-ק-ר-ש-ת

A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
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[Marcel Wiesweg]

> Hi,
>
> I like it a lot, that a user can scroll in-between the views of his
> RAWs in digiKam very fast.
>
> Out of curiosity and because I couldn't find infos in the handbook
> about that feature:
> How did you realized such a fast viewing for such big files?
> Just the concept, technical details are not important.

Short answer: Don't load the big file, load the small file.
Most RAW files have an embedded preview which is already generated by the
camera when creating the file. The camera has obviously the same problem with
displaying big files on its display as we have. If such a preview is
available, we use it in the preview mode (you can opt to always view the full
size image in the setup).
If no preview is available, we will use the fastest method for decoding a RAW
file available from dcraw, but in this case, loading is slow.

>
> I looked into the albums and into the directory
> ".kde/share/apps/digikam" but I did not find any cache.

We dont use an on-disk cache for preview, they are too large. Thumbnails are
stored on disk of course.

>
> Andreas


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[Gilles Caulier-4]

2008/5/11 Marcel Wiesweg <[hidden email]>:

>> Hi,
>>
>> I like it a lot, that a user can scroll in-between the views of his
>> RAWs in digiKam very fast.
>>
>> Out of curiosity and because I couldn't find infos in the handbook
>> about that feature:
>> How did you realized such a fast viewing for such big files?
>> Just the concept, technical details are not important.
>
> Short answer: Don't load the big file, load the small file.
> Most RAW files have an embedded preview which is already generated by the
> camera when creating the file. The camera has obviously the same problem with
> displaying big files on its display as we have. If such a preview is
> available, we use it in the preview mode (you can opt to always view the full
> size image in the setup).
> If no preview is available, we will use the fastest method for decoding a RAW
> file available from dcraw, but in this case, loading is slow.
>

And another point. loading of preview is done using a separate thread
(multithreading)

If you have a double core computer, it faster. A dedicated CPU will be
used to do the job.

Gilles ( who is back from LGM2008 - Poland)
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[Andreas Borutta]

Marcel Wiesweg schrieb:

>> Out of curiosity and because I couldn't find infos in the handbook
>> about that feature:
>> How did you realized such a fast viewing for such big files?
>> Just the concept, technical details are not important.
>
> Short answer: Don't load the big file, load the small file.

[...]

Thanks for the answer. I did not know already that small files are
embedded in RAWs.

My first thought was, you are using a RAM caching:
Starting to render around 5 pictures before and after the one which
has the focus.
When a users scrolls to the next or previous picture, that type of
caching ensures, that a user gets the picture very fast.

Andreas
--
http://borumat.de

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[Marcel Wiesweg]

>
> Thanks for the answer. I did not know already that small files are
> embedded in RAWs.
>
> My first thought was, you are using a RAM caching:
> Starting to render around 5 pictures before and after the one which
> has the focus.
> When a users scrolls to the next or previous picture, that type of
> caching ensures, that a user gets the picture very fast.

Yes we are doing that as well. There is a cache in memory, and we preload the
next or previous picture in a different thread in the background. This is not
specific to RAW files of course. And as Gilles pointed out, we are strictly
using multithreading for all loading operations.


>
> Andreas


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