i remember an old discussion about channels which was a bit short on
references on why channels are an important concept. Although quite late
a tip (and written for photoshop CS4), the book mentionend in the subject
line can fill in the gap, i believe.
From a developer's point of view, it offers detailed descriptions how channels
and selection tools are actually used to accomplish complex selection and
tasks. It also provides an explanation for some of the UI idiosyncrasies and
associated to channels (channel were first, layers came later). Furthermore, it
(one) artist's view on blend modes.
Cheap-skate bonus: the book is out of print (e.g. 15€ @ terrashop.de)
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