diff --git a/martin/src/cog/errors.rs b/martin/src/cog/errors.rs
index 9998dc5b6..13e06f407 100644
--- a/martin/src/cog/errors.rs
+++ b/martin/src/cog/errors.rs
@@ -1,6 +1,6 @@
 use std::path::PathBuf;
 
-use png::EncodingError;
+use png::{ColorType, EncodingError};
 use tiff::TiffError;
 
 #[derive(thiserror::Error, Debug)]
@@ -37,4 +37,9 @@ pub enum CogError {
 
     #[error("Failed to write pixel bytes to png file at {0}: {1}")]
     WriteToPngFailed(PathBuf, EncodingError),
+
+    #[error(
+        "The bit depth {} of the tiff file {1} is not accepted by png crate when encoding tif chunk data to png"
+    )]
+    PngBitDepthNotAccepted(u8, PathBuf, ColorType),
 }
diff --git a/martin/src/cog/mod.rs b/martin/src/cog/mod.rs
index c6c118154..6bf0be40a 100644
--- a/martin/src/cog/mod.rs
+++ b/martin/src/cog/mod.rs
@@ -1,6 +1,7 @@
 mod errors;
 
 pub use errors::CogError;
+use png::BitDepth;
 use serde_yaml::with;
 
 use std::collections::HashMap;
@@ -114,23 +115,32 @@ impl Source for CogSource {
         let tile_height = decoder.chunk_dimensions().1;
         let (data_width, data_height) = decoder.chunk_data_dimensions(tile_idx);
         let png_bytes = match color_type {
-            ColorType::Gray(_) => todo!(),
+            ColorType::Gray(n_bits_per_sample) => gray_to_png(
+                decode_result,
+                tile_width,
+                tile_height,
+                data_width,
+                data_height,
+                &self.path,
+            ),
             ColorType::RGB(_) => rgb_to_png(
                 decode_result,
                 tile_width,
                 tile_height,
                 data_width,
                 data_height,
+                false,
                 &self.path,
             ),
             ColorType::Palette(_) => todo!(),
             ColorType::GrayA(_) => todo!(),
-            ColorType::RGBA(_) => rgba_to_png(
+            ColorType::RGBA(_) => rgb_to_png(
                 decode_result,
                 tile_width,
                 tile_height,
                 data_width,
                 data_height,
+                true,
                 &self.path,
             ),
             ColorType::CMYK(_) => todo!(),
@@ -141,7 +151,39 @@ impl Source for CogSource {
     }
 }
 
-fn rgba_to_png(
+fn gray_to_png(
+    data: DecodingResult,
+    tile_width: u32,
+    tile_height: u32,
+    data_width: u32,
+    data_height: u32,
+    path: &PathBuf,
+) -> Result<Vec<u8>, CogError> {
+    let is_padded = data_width != tile_width;
+
+    let mut buffer = Vec::new();
+    let mut encoder = png::Encoder::new(BufWriter::new(&mut buffer), tile_width, tile_height);
+    encoder.set_color(png::ColorType::Grayscale);
+    match data {
+        DecodingResult::U8(vec) => {
+            encoder.set_depth(BitDepth::Eight);
+
+            todo!()
+        }
+        DecodingResult::U16(vec) => todo!(),
+        DecodingResult::U32(vec) => todo!(),
+        DecodingResult::U64(vec) => todo!(),
+        DecodingResult::F32(vec) => todo!(),
+        DecodingResult::F64(vec) => todo!(),
+        DecodingResult::I8(vec) => todo!(),
+        DecodingResult::I16(vec) => todo!(),
+        DecodingResult::I32(vec) => todo!(),
+        DecodingResult::I64(vec) => todo!(),
+    }
+    todo!()
+}
+
+fn rgb_to_png(
     data: DecodingResult,
     tile_width: u32,
     tile_height: u32,
@@ -229,73 +271,6 @@ fn rgba_to_png(
     }
 }
 
-fn rgb_to_png(
-    data: DecodingResult,
-    tile_width: u32,
-    tile_height: u32,
-    data_width: u32,
-    data_height: u32,
-    path: &PathBuf,
-) -> Result<Vec<u8>, CogError> {
-    let is_padded = data_width != tile_width;
-    match data {
-        DecodingResult::U8(vec) => {
-            let mut buffer = Vec::new();
-            {
-                let w = BufWriter::new(&mut buffer);
-                let mut encoder = png::Encoder::new(w, tile_width, tile_height);
-                encoder.set_color(png::ColorType::Rgb);
-                encoder.set_depth(png::BitDepth::Eight);
-                let mut writer = encoder
-                    .write_header()
-                    .map_err(|e| CogError::WritePngHeaderFailed(path.clone(), e))?;
-                if is_padded {
-                    //todo the no_data value should read from the tiff file, or from configuration
-                    let arr =
-                        pad_data(0, &vec, tile_width, tile_height, data_width, data_height, 3);
-                    writer
-                        .write_image_data(&arr)
-                        .map_err(|e| CogError::WriteToPngFailed(path.clone(), e))?;
-                } else {
-                    writer
-                        .write_image_data(&vec)
-                        .map_err(|e| CogError::WriteToPngFailed(path.clone(), e))?;
-                }
-            }
-            Ok(buffer)
-        }
-        DecodingResult::U16(vec) => {
-            let mut buffer = Vec::new();
-            let w = BufWriter::new(&mut buffer);
-            let mut encoder = png::Encoder::new(w, tile_width, tile_height);
-            encoder.set_color(png::ColorType::Rgb);
-            encoder.set_depth(png::BitDepth::Sixteen);
-
-            if is_padded {
-                //todo the no_data value should read from the tiff file
-                let arr = pad_data(0, &vec, tile_width, tile_height, data_width, data_height, 3);
-                let u8_vec: &[u8] = bytemuck::cast_slice(&arr);
-                let mut writer = encoder
-                    .write_header()
-                    .map_err(|e| CogError::WriteToPngFailed(path.clone(), e))?;
-                writer
-                    .write_image_data(u8_vec)
-                    .map_err(|e| CogError::WriteToPngFailed(path.clone(), e))?;
-            } else {
-                let u8_vec: &[u8] = bytemuck::cast_slice(&vec);
-                let mut writer = encoder
-                    .write_header()
-                    .map_err(|e| CogError::WriteToPngFailed(path.clone(), e))?;
-                writer
-                    .write_image_data(u8_vec)
-                    .map_err(|e| CogError::WriteToPngFailed(path.clone(), e))?;
-            }
-            Ok(buffer)
-        }
-        _ => todo!(),
-    }
-}
-
 fn pad_data<T: Copy>(
     no_data: T,
     vec: &[T],