Add note on using -cw to the -esw help text
@@ -363,9 +363,17 @@ ADVANCED COMPRESSION
zero or one. For example to swap the RG channels, and replace
alpha with 1, the swizzle 'grb1' should be used.
- Note that the input swizzle is assumed to take place before any
- compression, and all error weighting applies to the post-swizzle
- channel ordering.
+ The input swizzle takes place before any compression, and all
+ error weighting applied using the -cw option is applied to the
+ post-swizzle channel ordering.
+
+ By default all 4 post-swizzle channels are included in the error
+ metrics during compression. When using -esw to map two channel
+ data to the L+A endpoint (e.g. -esw rrrg) the luminance data
+ stored in the rgb channels will be weighted three times more
+ strongly than the alpha channel. This can be corrected using the
+ -cw option to zero the weights of unused channels; e.g. using
+ -cw 1 0 0 1.
-dsw <swizzle>
Swizzle the color components after decompression. The swizzle is
