diff --git a/src/lib.rs b/src/lib.rs
index 085cce3c..6544ee59 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -248,7 +248,8 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
     Ok(())
 }
 
-/// Perform optimization on the input file using the options provided
+/// Perform optimization on the input file using the options provided, where the file is already
+/// loaded in-memory
 pub fn optimize_from_memory(data: &[u8], opts: &Options) -> Result<Vec<u8>, String> {
     // Read in the file and try to decode as PNG.
     if opts.verbosity.is_some() {
@@ -272,7 +273,7 @@ pub fn optimize_from_memory(data: &[u8], opts: &Options) -> Result<Vec<u8>, Stri
     }
 }
 
-/// Perform optimization on the input file using the options provided
+/// Perform optimization on the input PNG object using the options provided
 fn optimize_png(mut png: &mut png::PngData, file_original_size: usize, opts: &Options) -> Vec<u8> {
     type TrialWithData = (u8, u8, u8, u8, Vec<u8>);
 
diff --git a/src/png.rs b/src/png.rs
index c325ab45..2dbecf1e 100644
--- a/src/png.rs
+++ b/src/png.rs
@@ -306,6 +306,7 @@ impl PngData {
         return PngData::from_slice(&byte_data, fix_errors)
     }
 
+    /// Create a new `PngData` struct by reading a slice
     pub fn from_slice(byte_data: &[u8], fix_errors: bool) -> Result<PngData, String> {
         let mut byte_offset: usize = 0;
         // Test that png header is valid