diff --git a/src/reduction/alpha.rs b/src/reduction/alpha.rs
index 8be26072..de1499cd 100644
--- a/src/reduction/alpha.rs
+++ b/src/reduction/alpha.rs
@@ -1,24 +1,35 @@
 use png::PngData;
 
-pub fn reduce_alpha_channel(png: &mut PngData, bpp_factor: usize) -> Option<Vec<u8>> {
-    let mut reduced = Vec::with_capacity(png.raw_data.len());
+pub fn reduce_alpha_channel(png: &mut PngData, channels: usize) -> Option<Vec<u8>> {
     let byte_depth: u8 = png.ihdr_data.bit_depth.as_u8() >> 3;
-    let bpp: usize = bpp_factor * byte_depth as usize;
+    let bpp: usize = channels * byte_depth as usize;
     let colored_bytes = bpp - byte_depth as usize;
     for line in png.scan_lines() {
-        reduced.push(line.filter);
-        for (i, byte) in line.data.iter().enumerate() {
+        for (i, &byte) in line.data.iter().enumerate() {
             if i % bpp >= colored_bytes {
-                if *byte != 255 {
+                if byte != 255 {
                     return None;
                 }
-            } else {
-                reduced.push(*byte);
             }
         }
     }
+
+    let mut reduced = Vec::with_capacity(png.raw_data.len());
+    for line in png.scan_lines() {
+        reduced.push(line.filter);
+        for (i, &byte) in line.data.iter().enumerate() {
+            if i % bpp >= colored_bytes {
+                continue;
+            } else {
+                reduced.push(byte);
+            }
+        }
+    }
+
+    // sBIT contains information about alpha channel's original depth,
+    // and alpha has just been removed
     if let Some(sbit_header) = png.aux_headers.get_mut(&"sBIT".to_string()) {
-        assert_eq!(sbit_header.len(), bpp_factor);
+        assert_eq!(sbit_header.len(), channels);
         sbit_header.pop();
     }