[Koha-devel] Cover image 'thumbnail' size is bigger than 'imagefile' size

[Paul Poulain]

Hi Andreas,

(and if you can't provide a patch, please file a bug on buzilla, this 
description is perfect ! )

Le 12/12/2018 à 13:49, Jonathan Druart a écrit :
> Hi Andreas,
>
> This module has never been enhanced much and as you noticed there is
> room for such enhancements :)
> All of what you describe in your email makes sense to me, and I am
> sure the changes will be accepted if a patch is provided.
>
> Cheers,
> Jonathan
> Le mer. 12 déc. 2018 à 06:42, Andreas Roussos <arouss1980 at gmail.com> a écrit :
>> Dear Developers,
>>
>> 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)
>>
>> Thank you in advance for your time.
>>
>> Kind regards,
>> Andreas
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-- 
Paul Poulain, Associé-gérant / co-owner
BibLibre, Services en logiciels libres pour les bibliothèques
BibLibre, Open Source software and services for libraries