https://bugs.kde.org/show_bug.cgi?id=435377
Bug ID: 435377
Summary: Speed up image preview
Product: digikam
Version: 7.2.0
Platform: Microsoft Windows
OS: Microsoft Windows
Status: REPORTED
Severity: wishlist
Priority: NOR
Component: Preview-Image
Assignee: digikam-bugs-n...@kde.org
Reporter: philipp.k...@gmail.com
Target Milestone: ---
SUMMARY
I'm migrating from Picasa to digiKam. My photos are on an SSD. I copied one of
my (smaller) folder with photos so that it's "new" for both Picasa and digiKam.
Then, in each program, I double-click the first photo to open the larger view
and use the left/right arrow keys to navigate. Picasa reacts instantly, but
digiKam has a 300-500ms delay until the full image is displayed. It doesn't
hang, so I can navigate past 10 images as fast as I can press the key plus
500ms, but still it's annoying and makes it difficult to quickly compare
adjacent similar images.
STEPS TO REPRODUCE
1. Go to "Preview" mode on any album that has a couple photos in it.
2. Press the "right" key to navigate to the next photo.
OBSERVED RESULT
The UI takes several hundred milliseconds to update, for both the selection in
the image list at the top as well as the preview image below.
EXPECTED RESULT
Updates near-instantaneously (I believe I couldn't notice <50ms delays).
SOFTWARE/OS VERSIONS
Windows: 10
Linux/KDE Plasma: I'll test on this very soon and I strongly suspect it's the
same issue there.
KDE Frameworks Version: 5.78.0
Qt Version: 5.15.2
ADDITIONAL INFORMATION
tl;dr: Possible implementations are a look-ahead cache and, when that's not
enough, upsizing the thumbnail until the full image is loaded.
I have an SSD. Anyway I believe Picasa achieves this by pre-loading the next
2-5 photos into RAM and pre-rendering them to the resolution of the preview
image, so that when I press the button, only a few bytes need to be swapped out
in memory. When I click 4 photos ahead in Picasa, it also takes 500ms to load,
so presumably that wasn't cached yet, which is fine. But still it immediately
displays an upsized thumbnail, which looks quite fast/smooth with only a minor
glitch when the full-resolution image is displayed shortly after.
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