diff --git a/rtiow/src/renderer.rs b/rtiow/src/renderer.rs
index 7823448..5355e9d 100644
--- a/rtiow/src/renderer.rs
+++ b/rtiow/src/renderer.rs
@@ -146,9 +146,12 @@ pub struct Opt {
     /// Sub-samples per pixel
     #[structopt(short = "s", long = "subsample", default_value = "8")]
     pub subsamples: usize,
+    /// Use adaptive subsampling
+    #[structopt(long = "adaptive")]
+    pub adaptive_subsampling: bool,
     /// Select scene to render, one of: "bench", "book", "tutorial", "bvh", "test", "cornell_box",
     /// "cornell_smoke", "perlin_debug", "final"
-    #[structopt(long = "model", default_value = "perlin_debug")]
+    #[structopt(long = "model", default_value = "book")]
     pub model: Model,
     /// Path to store pprof profile data, i.e. /tmp/cpuprofile.pprof
     #[structopt(long = "pprof", parse(from_os_str))]
@@ -180,6 +183,8 @@ pub struct Scene {
     pub world: Box<dyn Hit>,
     pub camera: Camera,
     pub subsamples: usize,
+    /// overrides subsamples setting.
+    pub adaptive_subsampling: bool,
     pub num_threads: Option<usize>,
     pub width: usize,
     pub height: usize,
@@ -214,6 +219,7 @@ impl Default for Scene {
             )),
             camera,
             subsamples: 0,
+            adaptive_subsampling: false,
             num_threads: None,
             width: 0,
             height: 0,
@@ -304,10 +310,14 @@ static PIXEL_COUNT: AtomicUsize = AtomicUsize::new(0);
 
 fn render_pixel(scene: &Scene, x: usize, y: usize) -> Vec3 {
     let mut pixel: Vec3 = Default::default();
-    for _ in 0..scene.subsamples {
-        pixel = pixel + trace_pixel(x, y, scene);
-    }
-    pixel = pixel / scene.subsamples as f32;
+    let pixel = if scene.adaptive_subsampling {
+        Default::default()
+    } else {
+        for _ in 0..scene.subsamples {
+            pixel = pixel + trace_pixel(x, y, scene);
+        }
+        pixel / scene.subsamples as f32
+    };
     // Gamma correct, use gamma 2 correction, which is 1/gamma where gamma=2 which is 1/2 or
     // sqrt.
     PIXEL_COUNT.fetch_add(1, Ordering::SeqCst);
@@ -351,6 +361,7 @@ pub fn render(scene: Scene, output_dir: &Path) -> std::result::Result<(), std::i
     let scene = Arc::new(scene);
     let pixel_req_rx = Arc::new(Mutex::new(pixel_req_rx));
     info!("Creating {} render threads", num_threads);
+    info!("Adaptive subsampling: {}", scene.adaptive_subsampling);
     for i in 0..num_threads {
         let s = sync::Arc::clone(&scene);
         let pixel_req_rx = pixel_req_rx.clone();
diff --git a/rtiow/src/scenes/book.rs b/rtiow/src/scenes/book.rs
index fd2cea0..649bcad 100644
--- a/rtiow/src/scenes/book.rs
+++ b/rtiow/src/scenes/book.rs
@@ -51,6 +51,7 @@ pub fn new(opt: &Opt) -> Scene {
         camera,
         world,
         subsamples: opt.subsamples,
+        adaptive_subsampling: opt.adaptive_subsampling,
         num_threads: opt.num_threads,
         width: opt.width,
         height: opt.height,