https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=21987
Bug ID: 21987
Summary: Local cover 'thumbnail' size is bigger than
'imagefile' size in biblioimages table
Change sponsored?: ---
Product: Koha
Version: master
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P3
Component: Architecture, internals, and plumbing
Assignee: [email protected]
Reporter: [email protected]
QA Contact: [email protected]
We use local cover images in our setup, and also resize the covers
we scan to a width of 160px before uploading and attaching them to
a Koha bibliographic record (we upload one cover per biblio).
While using phpMyAdmin to view the contents of the 'biblioimages'
table (relevant screenshot here: https://imgur.com/a/cSEVLBI), we
noticed that the size of the BLOBs for the 'thumbnail' column was in
some cases twice as big as that of the 'imagefile' column. In fact,
this happens for more than 50% of uploaded covers as you can see
from the output of the SQL queries below:
mysql> SELECT COUNT( * ) AS count
FROM biblioimages
WHERE LENGTH( thumbnail ) > ( LENGTH( imagefile ) * 2 ) ;
+-------+
| count |
+-------+
| 1356 |
+-------+
mysql> SELECT COUNT( * ) AS count,
SUM( LENGTH( imagefile ) ) AS images_size,
SUM( LENGTH( thumbnail ) ) AS thumbnails_size
FROM biblioimages ;
+-------+-------------+-----------------+
| count | images_size | thumbnails_size |
+-------+-------------+-----------------+
| 2347 | 68323933 | 115839686 |
+-------+-------------+-----------------+
It would appear that for each 160px-wide JPG with 24-bit depth that
we have uploaded, the 'imagefile' column has been populated with an
PNG of 8-bit depth with the same dimensions as the uploaded file,
whereas the 'thumbnail' column contains a 24-bit PNG image with a
width reduced to 140 pixels.
I've tracked down the creation of resized 24-bit PNGs to this code:
https://github.com/Koha-Community/Koha/blob/master/C4/Images.pm#L182-L183
Do thumbnails for covers need to be true colour (24-bit) images?
Also, why is it that _scale_image() returns an image of 8-bit depth
if the source image's dimensions are less than 600x800? (i.e. when
no resizing is performed)
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