Created attachment 181853 [details]
Screenshot showing issue

SUMMARY
When "Checkerboard background" or "Solid color background" is selected in Configure -> Image View -> Show transparency with, the background area does not have the correct dimensions, so it does not cover the whole image.

STEPS TO REPRODUCE
1. Change the settings to one of the options mentions aboved
2. Open any image with transparency. For example, the Blue Transparent KDE logo (https://kde.org/stuff/clipart/logo/kde-logo-blue-transparent-3000x3000.png)

OBSERVED RESULT
The background does not have the correct dimensions. These dimensions are also wrongly affected by the zoom level.

EXPECTED RESULT
The background dimensions should match the image dimensions, and resize accordingly with the zoom levels.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.3.90
KDE Frameworks Version: 6.14.0
Qt Version: 6.9.0
Kernel Version: 6.14.7-arch2-1 (64-bit)
Graphics Platform: Wayland
Processors: 22 × Intel® Core™ Ultra 7 155H
Memory: 32 GiB of RAM (30.9 GiB usable)
Graphics Processor: Intel® Arc
Manufacturer: LENOVO
Product Name: 21KDS00600
System Version: ThinkPad X1 Carbon Gen 12