appendは"+"で横、"-"で縦につなぎます
実際のところ
"+"のとき
$ convert -size 30x30 xc:black -fill white -draw 'circle 15,15 5,15' \
\( +clone -shade 110x90 -normalize -negate -alpha Off \) \
\( +clone -clone -2 -compose Plus -composite \) \
\( -clone 0 -shade 110x50 -normalize -alpha Off \) \
\( +clone -gamma 1,0,0 \) \
\( -clone 2,-1 -compose Multiply -composite \) \
+append seq_process_fx.gif
"-"のとき
$ convert -size 30x30 xc:black -fill white -draw 'circle 15,15 5,15' \
\( +clone -shade 110x90 -normalize -negate -alpha Off \) \
\( +clone -clone -2 -compose Plus -composite \) \
\( -clone 0 -shade 110x50 -normalize -alpha Off \) \
\( +clone -gamma 1,0,0 \) \
\( -clone 2,-1 -compose Multiply -composite \) \
-append seq_process_fx.gif