diff --git a/draw/gen.go b/draw/gen.go
index cb5e12f..b02368a 100644
--- a/draw/gen.go
+++ b/draw/gen.go
@@ -366,48 +366,28 @@
 			default:
 				log.Fatalf("bad dType %q", d.dType)
 			case "Image":
-				switch d.sType {
-				default:
-					return argf(args, ""+
-						"if dstMask != nil {\n"+
-						"	qr, qg, qb, qa := dst.At($0, $1).RGBA()\n"+
-						"	_, _, _, ma := dstMask.At(dmp.X + $0, dmp.Y + $1).RGBA()\n"+
-						"	pr = pr * ma / 0xffff\n"+
-						"	pg = pg * ma / 0xffff\n"+
-						"	pb = pb * ma / 0xffff\n"+
-						"	pa = pa * ma / 0xffff\n"+
-						"	$2a1 := 0xffff - ma\n"+ // Note that this is ma, not $2a.
-						"	dstColorRGBA64.R = uint16(qr*$2a1/0xffff + $2r)\n"+
-						"	dstColorRGBA64.G = uint16(qg*$2a1/0xffff + $2g)\n"+
-						"	dstColorRGBA64.B = uint16(qb*$2a1/0xffff + $2b)\n"+
-						"	dstColorRGBA64.A = uint16(qa*$2a1/0xffff + $2a)\n"+
-						"	dst.Set($0, $1, dstColor)\n"+
-						"} else {\n"+
-						"	dstColorRGBA64.R = uint16($2r)\n"+
-						"	dstColorRGBA64.G = uint16($2g)\n"+
-						"	dstColorRGBA64.B = uint16($2b)\n"+
-						"	dstColorRGBA64.A = uint16($2a)\n"+
-						"	dst.Set($0, $1, dstColor)\n"+
-						"}",
-					)
-				case "*image.Gray":
-					return argf(args, ""+
-						"out := uint16($2r)\n"+
-						"dstColorRGBA64.R = out\n"+
-						"dstColorRGBA64.G = out\n"+
-						"dstColorRGBA64.B = out\n"+
-						"dstColorRGBA64.A = 0xffff\n"+
-						"dst.Set($0, $1, dstColor)",
-					)
-				case "*image.YCbCr":
-					return argf(args, ""+
-						"dstColorRGBA64.R = uint16($2r)\n"+
-						"dstColorRGBA64.G = uint16($2g)\n"+
-						"dstColorRGBA64.B = uint16($2b)\n"+
-						"dstColorRGBA64.A = 0xffff\n"+
-						"dst.Set($0, $1, dstColor)",
-					)
-				}
+				return argf(args, ""+
+					"if dstMask != nil {\n"+
+					"	qr, qg, qb, qa := dst.At($0, $1).RGBA()\n"+
+					"	_, _, _, ma := dstMask.At(dmp.X + $0, dmp.Y + $1).RGBA()\n"+
+					"	pr = pr * ma / 0xffff\n"+
+					"	pg = pg * ma / 0xffff\n"+
+					"	pb = pb * ma / 0xffff\n"+
+					"	pa = pa * ma / 0xffff\n"+
+					"	$2a1 := 0xffff - ma\n"+ // Note that this is ma, not $2a.
+					"	dstColorRGBA64.R = uint16(qr*$2a1/0xffff + $2r)\n"+
+					"	dstColorRGBA64.G = uint16(qg*$2a1/0xffff + $2g)\n"+
+					"	dstColorRGBA64.B = uint16(qb*$2a1/0xffff + $2b)\n"+
+					"	dstColorRGBA64.A = uint16(qa*$2a1/0xffff + $2a)\n"+
+					"	dst.Set($0, $1, dstColor)\n"+
+					"} else {\n"+
+					"	dstColorRGBA64.R = uint16($2r)\n"+
+					"	dstColorRGBA64.G = uint16($2g)\n"+
+					"	dstColorRGBA64.B = uint16($2b)\n"+
+					"	dstColorRGBA64.A = uint16($2a)\n"+
+					"	dst.Set($0, $1, dstColor)\n"+
+					"}",
+				)
 			case "*image.RGBA":
 				switch d.sType {
 				default:
@@ -488,48 +468,28 @@
 			default:
 				log.Fatalf("bad dType %q", d.dType)
 			case "Image":
-				switch d.sType {
-				default:
-					ret = argf(args, ""+
-						"if dstMask != nil {\n"+
-						"	qr, qg, qb, qa := dst.At($0, $1).RGBA()\n"+
-						"	_, _, _, ma := dstMask.At(dmp.X + $0, dmp.Y + $1).RGBA()\n"+
-						"	pr := uint32($2($3r * $4)) * ma / 0xffff\n"+
-						"	pg := uint32($2($3g * $4)) * ma / 0xffff\n"+
-						"	pb := uint32($2($3b * $4)) * ma / 0xffff\n"+
-						"	pa := uint32($2($3a * $4)) * ma / 0xffff\n"+
-						"	pa1 := 0xffff - ma\n"+ // Note that this is ma, not pa.
-						"	dstColorRGBA64.R = uint16(qr*pa1/0xffff + pr)\n"+
-						"	dstColorRGBA64.G = uint16(qg*pa1/0xffff + pg)\n"+
-						"	dstColorRGBA64.B = uint16(qb*pa1/0xffff + pb)\n"+
-						"	dstColorRGBA64.A = uint16(qa*pa1/0xffff + pa)\n"+
-						"	dst.Set($0, $1, dstColor)\n"+
-						"} else {\n"+
-						"	dstColorRGBA64.R = $2($3r * $4)\n"+
-						"	dstColorRGBA64.G = $2($3g * $4)\n"+
-						"	dstColorRGBA64.B = $2($3b * $4)\n"+
-						"	dstColorRGBA64.A = $2($3a * $4)\n"+
-						"	dst.Set($0, $1, dstColor)\n"+
-						"}",
-					)
-				case "*image.Gray":
-					ret = argf(args, ""+
-						"out := $2($3r * $4)\n"+
-						"dstColorRGBA64.R = out\n"+
-						"dstColorRGBA64.G = out\n"+
-						"dstColorRGBA64.B = out\n"+
-						"dstColorRGBA64.A = 0xffff\n"+
-						"dst.Set($0, $1, dstColor)",
-					)
-				case "*image.YCbCr":
-					ret = argf(args, ""+
-						"dstColorRGBA64.R = $2($3r * $4)\n"+
-						"dstColorRGBA64.G = $2($3g * $4)\n"+
-						"dstColorRGBA64.B = $2($3b * $4)\n"+
-						"dstColorRGBA64.A = 0xffff\n"+
-						"dst.Set($0, $1, dstColor)",
-					)
-				}
+				ret = argf(args, ""+
+					"if dstMask != nil {\n"+
+					"	qr, qg, qb, qa := dst.At($0, $1).RGBA()\n"+
+					"	_, _, _, ma := dstMask.At(dmp.X + $0, dmp.Y + $1).RGBA()\n"+
+					"	pr := uint32($2($3r * $4)) * ma / 0xffff\n"+
+					"	pg := uint32($2($3g * $4)) * ma / 0xffff\n"+
+					"	pb := uint32($2($3b * $4)) * ma / 0xffff\n"+
+					"	pa := uint32($2($3a * $4)) * ma / 0xffff\n"+
+					"	pa1 := 0xffff - ma\n"+ // Note that this is ma, not pa.
+					"	dstColorRGBA64.R = uint16(qr*pa1/0xffff + pr)\n"+
+					"	dstColorRGBA64.G = uint16(qg*pa1/0xffff + pg)\n"+
+					"	dstColorRGBA64.B = uint16(qb*pa1/0xffff + pb)\n"+
+					"	dstColorRGBA64.A = uint16(qa*pa1/0xffff + pa)\n"+
+					"	dst.Set($0, $1, dstColor)\n"+
+					"} else {\n"+
+					"	dstColorRGBA64.R = $2($3r * $4)\n"+
+					"	dstColorRGBA64.G = $2($3g * $4)\n"+
+					"	dstColorRGBA64.B = $2($3b * $4)\n"+
+					"	dstColorRGBA64.A = $2($3a * $4)\n"+
+					"	dst.Set($0, $1, dstColor)\n"+
+					"}",
+				)
 			case "*image.RGBA":
 				switch d.sType {
 				default: