One online tool for BASE64 is Motobit Software's BASE64 encoder/decoder.
To use it to convert StarTools masks back into importable PNG files;
This should result in a download of the mask as a PNG file which can be imported into the StarTools mask editor, as welll as other applications.
Exclusive to the main screen, the buttons that activate the different modules, reside on the left hand side of the main screen.
StarTools' Deconvolution module allows for recovering detail in seeing-limited and diffraction-limited datasets.
StarTools' Detail-aware Wavelet Sharpening allows you to bring out faint structural detail in your images.
You can convert everything you see to a format you find convenient. Give it a try!