One online tool for BASE64 is Motobit Software's BASE64 encoder/decoder.
Simply paste the BASE64 code into the text box, select the decode the data from a Base64 string (base64 decoding) radio button, as well as the export to a binary file, filename: radio button. Name the file for example "mask.png" and click the convert the source data button.
This should result in a download of the mask as a PNG file.
Thank you StarTools for turning my average photos into amazing ones.
If your data is very noisy, it is possible AutoDev will optimise for the noise, mistaking it for real detail.
A StarTools license is currently priced at 65 AUD (approximately 50 USD, 45 EUR, or 40 GBP).
Some of these solution provide basic post-processing function as well.
Never download StarTools from anywhere else but startools.org.
You can convert everything you see to a format you find convenient. Give it a try!