diff --git a/CHANGELOG.md b/CHANGELOG.md
index b4039abe..ea721276 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
  - Fix program version that is displayed when running `oxipng -V`
  - Ensure `--quiet` mode is actually quiet (@SethDusek [#20](https://github.com/shssoichiro/oxipng/pull/20))
  - Imply `--quiet` when `--stdout` is enabled
+ - Use heuristics to determine best combination for `-o1` ([#21](https://github.com/shssoichiro/oxipng/issues/21))
 
 **Version 0.1.1**
  - Fix `oxipng *` writing all input files to one output file ([#15](https://github.com/shssoichiro/oxipng/issues/15))
diff --git a/src/lib.rs b/src/lib.rs
index 773048aa..46334abe 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -41,11 +41,14 @@ pub struct Options {
     pub palette_reduction: bool,
     pub idat_recoding: bool,
     pub strip: bool,
+    pub use_heuristics: bool,
 }
 
 pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
     // Decode PNG from file
-    if opts.verbosity.is_some() { println!("Processing: {}", filepath.to_str().unwrap()) };
+    if opts.verbosity.is_some() {
+        println!("Processing: {}", filepath.to_str().unwrap())
+    };
     let in_file = Path::new(filepath);
     let mut png = match png::PngData::new(&in_file) {
         Ok(x) => x,
@@ -73,6 +76,31 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
         println!("    File size = {} bytes", file_original_size);
     }
 
+    let mut filter = opts.filter.clone();
+    let compression = opts.compression.clone();
+    let memory = opts.memory.clone();
+    let mut strategies = opts.strategies.clone();
+
+    if opts.use_heuristics {
+        // Heuristically determine which set of options to use
+        if png.ihdr_data.bit_depth.as_u8() >= 8 &&
+           png.ihdr_data.color_type != png::ColorType::Indexed {
+            if filter.is_empty() {
+                filter.insert(5);
+            }
+            if strategies.is_empty() {
+                strategies.insert(1);
+            }
+        } else {
+            if filter.is_empty() {
+                filter.insert(0);
+            }
+            if strategies.is_empty() {
+                strategies.insert(0);
+            }
+        }
+    }
+
     let mut something_changed = false;
 
     if opts.bit_depth_reduction {
@@ -118,16 +146,17 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
     if opts.idat_recoding || something_changed {
         // Go through selected permutations and determine the best
         let mut best: Option<(u8, u8, u8, u8, Vec<u8>)> = None;
-        let combinations = opts.filter.len() * opts.compression.len() * opts.memory.len() *
-                           opts.strategies.len();
+        let combinations = filter.len() * compression.len() * memory.len() * strategies.len();
         let mut results = Vec::with_capacity(combinations);
-        if opts.verbosity.is_some() { println!("Trying: {} combinations", combinations) };
+        if opts.verbosity.is_some() {
+            println!("Trying: {} combinations", combinations)
+        };
         crossbeam::scope(|scope| {
-            for f in &opts.filter {
+            for f in &filter {
                 let filtered = png.filter_image(*f);
-                for zc in &opts.compression {
-                    for zm in &opts.memory {
-                        for zs in &opts.strategies {
+                for zc in &compression {
+                    for zm in &memory {
+                        for zs in &strategies {
                             let moved_filtered = filtered.clone();
                             results.push(scope.spawn(move || {
                                 let new_idat = match deflate::deflate::deflate(&moved_filtered,
@@ -173,13 +202,13 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
         if let Some(better) = best {
             png.idat_data = better.4.clone();
             if opts.verbosity.is_some() {
-            println!("Found better combination:");
-            println!("    zc = {}  zm = {}  zs = {}  f = {}        {} bytes",
-                     better.1,
-                     better.2,
-                     better.3,
-                     better.0,
-                     png.idat_data.len());
+                println!("Found better combination:");
+                println!("    zc = {}  zm = {}  zs = {}  f = {}        {} bytes",
+                         better.1,
+                         better.2,
+                         better.3,
+                         better.0,
+                         png.idat_data.len());
             }
         }
     }
@@ -240,25 +269,25 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
     if opts.verbosity.is_some() {
         if idat_original_size >= png.idat_data.len() {
             println!("    IDAT size = {} bytes ({} bytes decrease)",
-                    png.idat_data.len(),
-                    idat_original_size - png.idat_data.len());
+                     png.idat_data.len(),
+                     idat_original_size - png.idat_data.len());
         } else {
             println!("    IDAT size = {} bytes ({} bytes increase)",
-                    png.idat_data.len(),
-                    png.idat_data.len() - idat_original_size);
+                     png.idat_data.len(),
+                     png.idat_data.len() - idat_original_size);
         }
         if file_original_size >= output_data.len() {
             println!("    file size = {} bytes ({} bytes = {:.2}% decrease)",
-                    output_data.len(),
-                    file_original_size - output_data.len(),
-                    (file_original_size - output_data.len()) as f64 / file_original_size as f64 *
-                    100f64);
+                     output_data.len(),
+                     file_original_size - output_data.len(),
+                     (file_original_size - output_data.len()) as f64 / file_original_size as f64 *
+                     100f64);
         } else {
             println!("    file size = {} bytes ({} bytes = {:.2}% increase)",
-                    output_data.len(),
-                    output_data.len() - file_original_size,
-                    (output_data.len() - file_original_size) as f64 / file_original_size as f64 *
-                    100f64);
+                     output_data.len(),
+                     output_data.len() - file_original_size,
+                     (output_data.len() - file_original_size) as f64 / file_original_size as f64 *
+                     100f64);
         }
     }
     Ok(())
diff --git a/src/main.rs b/src/main.rs
index 989473f0..59f1093f 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -46,6 +46,7 @@ fn main() {
         palette_reduction: true,
         idat_recoding: true,
         strip: false,
+        use_heuristics: false,
     };
 
     let matches = App::new("oxipng")
@@ -202,7 +203,7 @@ fn main() {
                                .long("strip"))
                       .after_help("Optimization levels:
     -o 0		=>	--zc 3 --nz				(0 or 1 trials)
-    -o 1		=>	--zc 9					(1 trial)
+    -o 1		=>	--zc 9					(1 trial, determined heuristically)
     -o 2		=>	--zc 9 --zs 0-3 --f 0,5			(8 trials)
     -o 3		=>	--zc 9 --zm 8-9 --zs 0-3 --f 0,5	(16 trials)
     -o 4		=>	--zc 9 --zm 8-9 --zs 0-3 --f 0-5	(48 trials)
@@ -268,12 +269,11 @@ fn parse_opts_into_struct(matches: &ArgMatches, opts: &mut oxipng::Options) -> R
             opts.compression = compression;
         }
         Some("1") => {
-            let mut filter = HashSet::new();
-            filter.insert(0);
+            let filter = HashSet::new();
             opts.filter = filter;
-            let mut strategies = HashSet::new();
-            strategies.insert(0);
+            let strategies = HashSet::new();
             opts.strategies = strategies;
+            opts.use_heuristics = true;
         }
         // 2 is the default
         Some("3") => {
diff --git a/src/png.rs b/src/png.rs
index a3f73b74..91d5b052 100644
--- a/src/png.rs
+++ b/src/png.rs
@@ -68,7 +68,7 @@ impl fmt::Display for BitDepth {
 }
 
 impl BitDepth {
-    fn as_u8(&self) -> u8 {
+    pub fn as_u8(&self) -> u8 {
         match *self {
             BitDepth::One => 1,
             BitDepth::Two => 2,
@@ -77,7 +77,7 @@ impl BitDepth {
             BitDepth::Sixteen => 16,
         }
     }
-    fn from_u8(depth: u8) -> BitDepth {
+    pub fn from_u8(depth: u8) -> BitDepth {
         match depth {
             1 => BitDepth::One,
             2 => BitDepth::Two,
diff --git a/tests/filters.rs b/tests/filters.rs
index d10d23ed..600aa6b3 100644
--- a/tests/filters.rs
+++ b/tests/filters.rs
@@ -45,6 +45,7 @@ fn get_opts(input: &Path) -> oxipng::Options {
         palette_reduction: true,
         idat_recoding: true,
         strip: false,
+        use_heuristics: false,
     }
 }
 
diff --git a/tests/flags.rs b/tests/flags.rs
index c69913ed..f1381b7d 100644
--- a/tests/flags.rs
+++ b/tests/flags.rs
@@ -45,6 +45,7 @@ fn get_opts(input: &Path) -> oxipng::Options {
         palette_reduction: true,
         idat_recoding: true,
         strip: false,
+        use_heuristics: false,
     }
 }
 
diff --git a/tests/reduction.rs b/tests/reduction.rs
index 3662302e..854eb662 100644
--- a/tests/reduction.rs
+++ b/tests/reduction.rs
@@ -45,6 +45,7 @@ fn get_opts(input: &Path) -> oxipng::Options {
         palette_reduction: true,
         idat_recoding: true,
         strip: false,
+        use_heuristics: false,
     }
 }