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