You have to be careful with masks in Paint Shop Pro; it's easy to get caught out.  For this example of using masks, the final output file will be a PNG, as they support an alpha transparency layer, which a mask is usually used to generate.

Don't let the documentation fool you; a Paint Shop Pro .MSK file is not some 'special format'.  It is a Windows bitmap file, 256 colours grayscale, with its extension renamed from .BMP to .MSK.  A sample image, '_Sample.msk', is saved in this directory; it has the correct 256 greyscale colours to create a mask from.  You can easily load these files by choosing 'Masks | Load from disk', and selecting such a file.

For this example, use a 50x50 image.  The _Sample.msk file is this size, and it will give a good example of how to deal with a mask.  Colour the image, say, red.  There shouldn't be any pre-existing masks loaded.  Now, choose 'Masks | Load from disk', and select the _Sample.msk file.  Voila!  One mask applied to the image, so it should fade off to the bottom-right.  This masked image can now be saved as a Paint Shop Pro file.

Indeed, it must be saved as a Paint Shop Pro file because - here comes the important bit - PAINT SHOP PRO MASKS ARE NOT AUTOMATICALLY CONVERTED TO ALPHA CHANNELS!!!

If you save that image as a PNG at the moment, it will NOT have an alpha channel.  A PSP mask and an image's alpha channel are distinct, which is why the options exist to 'save to alpha channel' and 'load from alpha channel' - it means you're saving the current Paint Shop Pro mask to or loading it from the alpha channel.  Think of them as 2 separate masks on the image.  The Paint Shop Pro mask is the 'working' mask that you will use whilst you want to edit the image.  The alpha channel is the final mask you apply once you've finished.

So, to business.  To save the mask to the image's alpha channel, choose 'Masks | Save to alpha channel'.  You'll see that there's an available alpha channel there (of course, as it's a Paint Shop Pro image currently, and they support alpha channels).  Click OK, and name the channel something like 'My alpha 1'.

Now you can actually save that alpha channel information to a PNG file.  'File | Save as', and save as a PNG file.  Open in something like a web browser that supports PNG alpha transparency to see that it's worked!

You can do plenty more with masks and alpha channels, including loading alpha channel information into a Paint Shop Pro mask again.  However, the important thing to remember (as this might well catch you out if you're wondering why a PNG doesn't have alpha channel information when you save it) is: PAINT SHOP PRO MASKS ARE NOT AUTOMATICALLY CONVERTED TO ALPHA CHANNELS!!!  You MUST manually save the alpha channel from the mask you've loaded.
