Bug 504241

While testing Krita, I was very impressed by its use of the .ora (OpenRaster) format. It’s a strong and future-proof storage concept, based on open standards like ZIP, XML, and PNG – which is highly appreciated. Well done!

However, there are some practical issues regarding how Krita handles .ora files during saving and exporting. Specifically, several additional files are always generated automatically, even if they are not required – and there is no way for users to disable or configure this behavior.

This leads to unnecessarily high storage usage, especially in environments with frequent saves and exports.
🔍 Current behavior:

1. mergedimage.png:
This is a full rendered composite of all visible layers. It serves no visible purpose inside the .ora archive, as Krita stores all layers individually. It is rarely needed, but easily adds 1 MB or more to every save.

2. thumbnail.png:
This file is used internally by Krita (e.g. the startup screen), but is ignored by operating systems such as Windows Explorer. It is often unnecessarily large – sometimes the same resolution as the project.
Suggestion: allow users to define a maximum size/resolution for the thumbnail in the settings.

3. .ora~ and other backup files:
When saving, Krita does not overwrite the file directly. Instead, it creates a complete backup (.ora~) in the same folder – without notice or option.
Even when exporting images (e.g. .webp, .png), if a file already exists, Krita creates a backup with a ~ suffix. Again, this happens silently and cannot be turned off.
💡 Additional note:

Instead of scattering backup copies across working directories, it would make more sense to offer a central backup folder with a maximum size limit – similar to how video editors manage autosaves.
Alternatively, old versions could be moved to the system trash/recycle bin, if desired.
🚨 Real-world impact:

In shared environments (network drives, cloud sync, multiple users), a simple .ora file that originally used 1 MB may easily grow to many times that size – just by saving or exporting as usual.
With two additional automated IT backups running in the background (which is standard in many environments), storage usage escalates drastically and silently.

Kind regards,  
Thomas