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.
Bin the image up until each pixel describes one unit of real detail.
StarTools works on all 32-bit (NT-based) and 64-bit versions of Windows.
High-resolution data sets, such as those from a DSLR typically require at least 4Gb of RAM.
StarTools uses all your CPU's cores to speed up processing in situations where it makes sense.
You can convert everything you see to a format you find convenient. Give it a try!