diff --git a/prototypes/xgb-image.go b/prototypes/xgb-image.go
index fce0ab1..c6ab02c 100644
--- a/prototypes/xgb-image.go
+++ b/prototypes/xgb-image.go
@@ -14,6 +14,7 @@ import (
 	"github.com/BurntSushi/xgb/xproto"
 
 	"image"
+	"image/color"
 	_ "image/gif"
 	_ "image/jpeg"
 	_ "image/png"
@@ -26,6 +27,47 @@ import "C"
 func F64ToFixed(f float64) render.Fixed { return render.Fixed(f * 65536) }
 func FixedToF64(f render.Fixed) float64 { return float64(f) / 65536 }
 
+var formats = map[byte]struct {
+	format    render.Directformat
+	transform func(color.Color) uint32
+}{
+	32: {
+		format: render.Directformat{
+			RedShift:   16,
+			RedMask:    0xff,
+			GreenShift: 8,
+			GreenMask:  0xff,
+			BlueShift:  0,
+			BlueMask:   0xff,
+			AlphaShift: 24,
+			AlphaMask:  0xff,
+		},
+		transform: func(color color.Color) uint32 {
+			r, g, b, a := color.RGBA()
+			return (a>>8)<<24 | (r>>8)<<16 | (g>>8)<<8 | (b >> 8)
+		},
+	},
+	30: {
+		/*
+			// Alpha makes compositing unbearably slow.
+			AlphaShift: 30,
+			AlphaMask:  0x3,
+		*/
+		format: render.Directformat{
+			RedShift:   20,
+			RedMask:    0x3ff,
+			GreenShift: 10,
+			GreenMask:  0x3ff,
+			BlueShift:  0,
+			BlueMask:   0x3ff,
+		},
+		transform: func(color color.Color) uint32 {
+			r, g, b, a := color.RGBA()
+			return (a>>14)<<30 | (r>>6)<<20 | (g>>6)<<10 | (b >> 6)
+		},
+	},
+}
+
 func main() {
 	/*
 		pf, err := os.Create("pprof.out")
@@ -63,18 +105,35 @@ func main() {
 	screen := setup.DefaultScreen(X)
 
 	visual, depth := screen.RootVisual, screen.RootDepth
-	// TODO: We should check that we find it, though we don't /need/ alpha here,
-	// it's just a minor improvement--affects the backpixel value.
+
+	// Only go for 10-bit when the picture can make use of that range.
+	prefer30 := false
+	switch img.(type) {
+	case *image.Gray16, *image.RGBA64, *image.NRGBA64:
+		prefer30 = true
+	}
+
+	// XXX: We don't /need/ alpha here, it's just a minor improvement--affects
+	// the backpixel value. (And we reject it in 30-bit depth anyway.)
 	for _, i := range screen.AllowedDepths {
 		for _, v := range i.Visuals {
 			// TODO: Could/should check other parameters.
-			if i.Depth == 32 && v.Class == xproto.VisualClassTrueColor {
+			if v.Class != xproto.VisualClassTrueColor {
+				continue
+			}
+			if prefer30 && i.Depth == 30 ||
+				!prefer30 && i.Depth == 32 {
 				visual, depth = v.VisualId, i.Depth
 				break
 			}
 		}
 	}
 
+	format, ok := formats[depth]
+	if !ok {
+		log.Fatalln("unsupported bit depth")
+	}
+
 	mid, err := xproto.NewColormapId(X)
 	if err != nil {
 		log.Fatalln(err)
@@ -92,7 +151,7 @@ func main() {
 	_ = xproto.CreateWindow(X, depth, wid, screen.Root,
 		0, 0, 500, 500, 0, xproto.WindowClassInputOutput,
 		visual, xproto.CwBackPixel|xproto.CwBorderPixel|xproto.CwEventMask|
-			xproto.CwColormap, []uint32{0x80808080, 0,
+			xproto.CwColormap, []uint32{format.transform(color.Alpha{0x80}), 0,
 			xproto.EventMaskStructureNotify | xproto.EventMaskExposure,
 			uint32(mid)})
 
@@ -132,7 +191,7 @@ func main() {
 	// setup.BitmapFormatScanline{Pad,Unit} and setup.BitmapFormatBitOrder
 	// don't interest us here since we're only using Z format pixmaps.
 	for _, pf := range setup.PixmapFormats {
-		if pf.Depth == 32 {
+		if pf.Depth == depth {
 			if pf.BitsPerPixel != 32 || pf.ScanlinePad != 32 {
 				log.Fatalln("unsuported X server")
 			}
@@ -143,28 +202,18 @@ func main() {
 	if err != nil {
 		log.Fatalln(err)
 	}
-	_ = xproto.CreatePixmap(X, 32, pixid, xproto.Drawable(screen.Root),
+	_ = xproto.CreatePixmap(X, depth, pixid, xproto.Drawable(screen.Root),
 		uint16(img.Bounds().Dx()), uint16(img.Bounds().Dy()))
 
 	var bgraFormat render.Pictformat
-	wanted := render.Directformat{
-		RedShift:   16,
-		RedMask:    0xff,
-		GreenShift: 8,
-		GreenMask:  0xff,
-		BlueShift:  0,
-		BlueMask:   0xff,
-		AlphaShift: 24,
-		AlphaMask:  0xff,
-	}
 	for _, pf := range pformats.Formats {
-		if pf.Depth == 32 && pf.Direct == wanted {
+		if pf.Depth == depth && pf.Direct == format.format {
 			bgraFormat = pf.Id
 			break
 		}
 	}
 	if bgraFormat == 0 {
-		log.Fatalln("ARGB format not found")
+		log.Fatalln("picture format not found")
 	}
 
 	// We could also look for the inverse pictformat.
@@ -202,14 +251,12 @@ func main() {
 		row := make([]byte, bounds.Dx()*4)
 		for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
 			for x := bounds.Min.X; x < bounds.Max.X; x++ {
-				r, g, b, a := img.At(x, y).RGBA()
-				encoding.PutUint32(row[x*4:],
-					(a>>8)<<24|(r>>8)<<16|(g>>8)<<8|(b>>8))
+				encoding.PutUint32(row[x*4:], format.transform(img.At(x, y)))
 			}
 			_ = xproto.PutImage(X, xproto.ImageFormatZPixmap,
 				xproto.Drawable(pixid), cid, uint16(bounds.Dx()), 1,
 				0, int16(y),
-				0, 32, row)
+				0, depth, row)
 		}
 	} else {
 		rep, err := shm.QueryVersion(X).Reply()
@@ -242,9 +289,7 @@ func main() {
 		for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
 			row := data[y*bounds.Dx()*4:]
 			for x := bounds.Min.X; x < bounds.Max.X; x++ {
-				r, g, b, a := img.At(x, y).RGBA()
-				encoding.PutUint32(row[x*4:],
-					(a>>8)<<24|(r>>8)<<16|(g>>8)<<8|(b>>8))
+				encoding.PutUint32(row[x*4:], format.transform(img.At(x, y)))
 			}
 		}
 
@@ -262,7 +307,7 @@ func main() {
 		_ = shm.PutImage(X, xproto.Drawable(pixid), cid,
 			uint16(bounds.Dx()), uint16(bounds.Dy()), 0, 0,
 			uint16(bounds.Dx()), uint16(bounds.Dy()), 0, 0,
-			32, xproto.ImageFormatZPixmap,
+			depth, xproto.ImageFormatZPixmap,
 			0 /* SendEvent */, segid, 0 /* Offset */)
 	}