Is your feature request related to a problem? Please describe.
GIF does not support alpha channel (transparent), so we see rare dots simulating transparency in GIFs

Describe the solution you'd like
Add option to

• enable transparency (like now)
• disable transparency making partially transparent pixels 100% transparent
• disable transparency making partially transparent pixels 0% transparent

Describe alternatives you've considered
No alternatives

Additional context
Animation from #96 (comment) can be used for tests