[Feature Request] Add automatic .png extension to output filename

[a2ush]

Request

Add automatic .png extension to output filename.
For example,

• If the user enters example as the filename, the tool should save the file as example.png.
• If the user enters example.png as the filename, the tool should keep the filename as is.

Background

Currently, when specifying a filename for the output file, if the .png extension is not included, the tool does not automatically append it. This can lead to confusion and errors, especially for users who are not familiar with file extensions.
To improve the user experience and prevent potential issues, it would be beneficial to implement a feature that automatically adds the .png extension to the output filename if it is not already present.