Mask in DjVu files

[ichnilatis]

Hi!
Could anybody explain to me what is a mask in a DjVu file?
I ask this in relation to the rendering mode of such files in KoReader.
Thank you.

[Frenzie]

https://www.epapyrus.jp/docs/djvuplu...g%20Layers.htm

In the DjVu format, a document is separated into a mask (or "foreground mask") and a background layer. The mask holds the sharp-edged elements such as text or distinct lines while the background contains fields of color with soft edges.

The mask is actually the black and white layer. Where does the color for the mask (i.e. for sharp elements and text) get stored? In two-layer documents, the mask layer has a palette of color information in it for rendering the mask in its proper hues. In three-layer documents, another separate layer called the foreground holds the color information for the mask.

[ichnilatis]

Thank you for your reply!
In a b/w DjVu document, which rendering mode is faster?
Thanks!