How to Recover Layer Masks From a Format Plugin

Hi !!

I am writing a format plugin that support multiple layers. Each of the layers can have their own mask (I need to be able to edit those masks).

When I try to save this multiple layers multiple masks image, I dont know how to access the layer mask data from the plugin. Anybody know how to do that? The 4th channel of the layer image is all white and does not look at all like my mask.

If I "apply the mask" to the layer before saving, then I can see the mask as a 4th channel in the plugin. However, by applying the mask, it is not editable anymore and lost forever  :-( .

Thanks!

Gilbert