diff --git a/cmd/pbr/main.go b/cmd/pbr/main.go
index 2cff8d4..4aecafd 100644
--- a/cmd/pbr/main.go
+++ b/cmd/pbr/main.go
@@ -5,6 +5,7 @@ import (
 	"os"
 	"strings"
 	"runtime/pprof"
+	"time"
 
 	"github.com/hunterloftis/pbr/pkg/camera"
 	"github.com/hunterloftis/pbr/pkg/env"
@@ -45,6 +46,20 @@ func stopProfile(f *os.File) {
        f.Close()
 }
 
+func startTimer(o *Options, s string) time.Time {
+	if o.Verbose {
+		fmt.Print(s)
+	}
+	return time.Now()
+}
+
+func stopTimer(o *Options, start time.Time) {
+	if o.Verbose {
+		elapsed := time.Since(start)
+		fmt.Printf("done: %s\n", elapsed.Round(time.Millisecond))
+	}
+}
+
 func run(o *Options) error {
 	if o.Profile {
 		f, err := createProfile()
@@ -54,10 +69,12 @@ func run(o *Options) error {
 		defer stopProfile(f)
 	}
 
+	start := startTimer(o, "Loading object file... ")
 	mesh, err := obj.ReadFile(o.Scene, true)
 	if err != nil {
 		return err
 	}
+	stopTimer(o, start)
 
 	if o.Scale != nil {
 		mesh.Scale(*o.Scale)
@@ -69,7 +86,9 @@ func run(o *Options) error {
 		m := materials[strings.ToLower(o.Material)]
 		mesh.SetMaterial(m)
 	}
+	start = startTimer(o, "Calculating mesh bounds... ")
 	bounds, surfaces := mesh.Bounds()
+	stopTimer(o, start)
 	camera := camera.NewSLR()
 	environment := render.Environment(env.NewGradient(rgb.Black, *o.Ambient, 3))
 
@@ -107,9 +126,12 @@ func run(o *Options) error {
 		surfaces = append(surfaces, sun)
 	}
 
+	start = startTimer(o, "Creating surface tree... ")
 	tree := surface.NewTree(surfaces...)
+	stopTimer(o, start)
 	scene := render.NewScene(camera, tree, environment)
 
 	fmt.Println("Surfaces:", len(surfaces))
-	return render.Iterative(scene, o.Out, o.Width, o.Height, o.Bounce, !o.Indirect)
+	limits := render.NewLimits(o.DumpPeriod, o.Time, o.Frames)
+	return render.Iterative(scene, limits, o.Out, o.Width, o.Height, o.Bounce, !o.Indirect)
 }
diff --git a/cmd/pbr/options.go b/cmd/pbr/options.go
index d77cebf..b388505 100644
--- a/cmd/pbr/options.go
+++ b/cmd/pbr/options.go
@@ -1,7 +1,6 @@
 package main
 
 import (
-	"math"
 	"path/filepath"
 
 	arg "github.com/alexflint/go-arg"
@@ -15,8 +14,9 @@ type Options struct {
 	Scene    string  `arg:"positional,required" help:"input scene .obj"`
 	Verbose  bool    `arg:"-v" help:"verbose output with scene information"`
 	Info     bool    `help:"output scene information and exit"`
-	Frames   float64 `arg:"-f" help:"number of frames at which to exit"`
-	Time     float64 `arg:"-t" help:"time to run before exiting (seconds)"`
+	DumpPeriod int `help:"how frequently to output progress frames"`
+	Frames   int `arg:"-f" help:"number of frames at which to exit"`
+	Time     int `arg:"-t" help:"time to run before exiting (seconds)"`
 	Material string  `help:"override material (glass, gold, mirror, plastic)"`
 
 	Width  int       `arg:"-w" help:"rendering width in pixels"`
@@ -57,8 +57,9 @@ func options() *Options {
 		Rad:        100,
 		Bounce:     6,
 		Indirect:   false,
-		Frames:     math.Inf(1),
-		Time:       math.Inf(1),
+		DumpPeriod: 6,
+		Frames:     0,
+		Time:       0,
 		Lens:       50,
 		FStop:      4,
 		Focus:      1,
diff --git a/examples/hello/hello.go b/examples/hello/hello.go
index 691ae2c..2a4dfa8 100644
--- a/examples/hello/hello.go
+++ b/examples/hello/hello.go
@@ -24,7 +24,7 @@ func main() {
 	e := env.NewGradient(rgb.Black, rgb.Energy{750, 750, 750}, 7)
 
 	scene := render.NewScene(c, s, e)
-	err := render.Iterative(scene, "hello.png", 898, 450, 8, true)
+	err := render.Iterative(scene, nil, "hello.png", 898, 450, 8, true)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "\nError: %v\n", err)
 	}
diff --git a/examples/redblue/redblue.go b/examples/redblue/redblue.go
index 364a3a1..2d2c2c5 100644
--- a/examples/redblue/redblue.go
+++ b/examples/redblue/redblue.go
@@ -44,5 +44,5 @@ func run() error {
 	tree := surface.NewTree(surfaces...)
 	scene := render.NewScene(camera, tree, environment)
 
-	return render.Iterative(scene, "redblue.png", 1280, 720, 6, true)
+	return render.Iterative(scene, nil, "redblue.png", 1280, 720, 6, true)
 }
diff --git a/examples/shapes/shapes.go b/examples/shapes/shapes.go
index cac2bff..885b6c5 100644
--- a/examples/shapes/shapes.go
+++ b/examples/shapes/shapes.go
@@ -48,5 +48,5 @@ func run() error {
 	)
 	scene := render.NewScene(cam, surf, sky)
 
-	return render.Iterative(scene, "shapes.png", 800, 450, 6, true)
+	return render.Iterative(scene, nil, "shapes.png", 800, 450, 6, true)
 }
diff --git a/examples/sponza/sponza.go b/examples/sponza/sponza.go
index 6527942..0f124a0 100644
--- a/examples/sponza/sponza.go
+++ b/examples/sponza/sponza.go
@@ -44,5 +44,5 @@ func run() error {
 	tree := surface.NewTree(surfaces...)
 	scene := render.NewScene(camera, tree, environment)
 
-	return render.Iterative(scene, "sponza.png", 1280, 720, 8, true)
+	return render.Iterative(scene, nil, "sponza.png", 1280, 720, 8, true)
 }
diff --git a/pkg/render/iterative.go b/pkg/render/iterative.go
index 7dcdd4b..fd5b8aa 100644
--- a/pkg/render/iterative.go
+++ b/pkg/render/iterative.go
@@ -14,14 +14,46 @@ import (
 	"golang.org/x/text/message"
 )
 
-func Iterative(scene *Scene, file string, width, height, depth int, direct bool) error {
+type Limits struct {
+	DumpPeriod time.Duration
+	Time       time.Duration
+	Frames     int
+}
+
+func NewLimits(d int, t int, f int) *Limits {
+	if d == 0 {
+		d = math.MaxInt32
+	}
+	if t == 0 {
+		t = math.MaxInt32
+	}
+	return &Limits{
+		DumpPeriod: time.Duration(d) * time.Second,
+		Time:       time.Duration(t) * time.Second,
+		Frames:     f,
+	}
+}
+
+func Iterative(scene *Scene, limits *Limits, file string, width, height, depth int, direct bool) error {
 	kill := make(chan os.Signal, 2)
 	signal.Notify(kill, os.Interrupt, syscall.SIGTERM)
 
+	if limits == nil {
+		limits = NewLimits(6, 0, 0)
+	}
+
 	frame := scene.Render(width, height, depth, direct)
 	defer frame.Stop()
-	ticker := time.NewTicker(6 * time.Second) // 10 .s = 1 minute, 100 .s = 1 hr
+	ticker := time.NewTicker(limits.DumpPeriod)
 	defer ticker.Stop()
+	limiter := time.NewTicker(limits.Time)
+	defer limiter.Stop()
+	framelim := time.NewTicker(1 * time.Second)
+	if limits.Frames == 0 {
+		framelim.Stop()
+	} else {
+		defer framelim.Stop()
+	}
 
 	start := time.Now().UnixNano()
 	max := 0
@@ -31,6 +63,14 @@ func Iterative(scene *Scene, file string, width, height, depth int, direct bool)
 		select {
 		case <-kill:
 			frame.Stop()
+		case <-limiter.C:
+			frame.Stop()
+			fmt.Printf("\nTime limit reached.\n")
+		case <-framelim.C:
+			if _, n := frame.Sample(); n > limits.Frames {
+				frame.Stop()
+				fmt.Print("\nFrame limit reached.\n")
+			}
 		case <-ticker.C:
 			if sample, n := frame.Sample(); n > max {
 				max = n
@@ -43,12 +83,16 @@ func Iterative(scene *Scene, file string, width, height, depth int, direct bool)
 	}
 
 	stop := time.Now().UnixNano()
-	sample, _ := frame.Sample()
+	sample, frames := frame.Sample()
 	total := sample.Total()
 	p := message.NewPrinter(language.English)
 	secs := float64(stop-start) / 1e9
 	sps := math.Round(float64(total) / secs) // TODO: rename to pixels/sec for clarity
 	p.Printf("\n%v samples in %.1f seconds (%.0f samples/sec)\n", total, secs, sps)
+	p.Printf("\n%v frames (%.1f frames/sec)\n", frames, float64(frames)/secs)
+	if err := writePng(file, sample.Image()); err != nil {
+		return err
+	}
 
 	return nil
 }