diff --git a/src/compression/CMakeLists.txt b/src/compression/CMakeLists.txt
index 27153ac..7eebe23 100644
--- a/src/compression/CMakeLists.txt
+++ b/src/compression/CMakeLists.txt
@@ -8,6 +8,7 @@ list(APPEND compression_LIB_INCLUDES
     DeflateEncoder.cpp
     DeflateBlock.cpp
     Lz77Encoder.cpp
+    CyclicRedundancyChecker.cpp
     )
 
 add_library(compression SHARED ${compression_LIB_INCLUDES})
diff --git a/src/compression/CyclicRedundancyChecker.cpp b/src/compression/CyclicRedundancyChecker.cpp
new file mode 100644
index 0000000..e69de29
diff --git a/src/compression/CyclicRedundancyChecker.h b/src/compression/CyclicRedundancyChecker.h
new file mode 100644
index 0000000..9d31d1e
--- /dev/null
+++ b/src/compression/CyclicRedundancyChecker.h
@@ -0,0 +1,52 @@
+#pragma once
+
+class CyclicRedundancyChecker
+{
+public:
+
+    void createTable()
+    {
+        unsigned long c{0};
+        for (int n = 0; n < 256; n++)
+        {
+            c = (unsigned long) n;
+            for (int k = 0; k < 8; k++)
+            {
+                if (c & 1)
+                {
+                    c = 0xedb88320L ^ (c >> 1);
+                }
+                else
+                {
+                    c = c >> 1;
+                }
+            }
+            mTable[n] = c;
+        }
+        mTableComputed = true;
+        mTableComputed = 1;
+    }
+
+    unsigned long updateCrc(unsigned long crc, unsigned char *buf, int len)
+    {
+        unsigned long c = crc;
+        if (!mTableComputed)
+        {
+            createTable();
+        }
+        for (int n = 0; n < len; n++)
+        {
+            c = mTable[(c ^ buf[n]) & 0xff] ^ (c >> 8);
+        }
+        return c;
+    }
+
+    unsigned long doCrc(unsigned char *buf, int len)
+    {
+        return updateCrc(0xffffffffL, buf, len) ^ 0xffffffffL;
+    }
+
+private:
+    bool mTableComputed{false};
+    unsigned long mTable[256];
+};
diff --git a/src/core/ByteUtils.cpp b/src/core/ByteUtils.cpp
index 25829c9..7ad14bb 100644
--- a/src/core/ByteUtils.cpp
+++ b/src/core/ByteUtils.cpp
@@ -21,6 +21,11 @@ unsigned char ByteUtils::getHigherNBits(unsigned char input, unsigned num)
     return input >> 8 - num;
 }
 
+unsigned char ByteUtils::getByteN(uint32_t input, unsigned n)
+{
+    return (input << 8*n) >> 24;
+}
+
 unsigned char ByteUtils::getLowerNBits(unsigned char input, unsigned num)
 {
     switch (num)
diff --git a/src/core/ByteUtils.h b/src/core/ByteUtils.h
index 096c8fc..a34c2ea 100644
--- a/src/core/ByteUtils.h
+++ b/src/core/ByteUtils.h
@@ -17,6 +17,8 @@ public:
 
     static Word GetWordLastByte(const Word word);
 
+    static unsigned char getByteN(uint32_t input, unsigned n);
+
     static unsigned char getHigherNBits(unsigned char input, unsigned num);
 
     static unsigned char getLowerNBits(unsigned char input, unsigned num);
diff --git a/src/core/file_utilities/File.cpp b/src/core/file_utilities/File.cpp
index 9c1f29c..2dde794 100644
--- a/src/core/file_utilities/File.cpp
+++ b/src/core/file_utilities/File.cpp
@@ -32,9 +32,23 @@ std::ofstream* File::GetOutHandle() const
     return mOutHandle.get();
 }
 
-unsigned char File::readNextByte()
+std::optional<unsigned char> File::readNextByte()
 {
-    return mInHandle->get();
+    if (mInHandle->good())
+    {
+        if (auto val = mInHandle->get(); val == EOF)
+        {
+            return std::nullopt;
+        }
+        else
+        {
+            return val;
+        }
+    }
+    else
+    {
+        return std::nullopt;
+    }
 }
 
 void File::Open(bool asBinary)
diff --git a/src/core/file_utilities/File.h b/src/core/file_utilities/File.h
index 1fe93e3..cf842c6 100644
--- a/src/core/file_utilities/File.h
+++ b/src/core/file_utilities/File.h
@@ -7,6 +7,7 @@
 #include <fstream>
 #include <memory>
 #include <vector>
+#include <optional>
 
 using Path = std::filesystem::path;
 
@@ -48,7 +49,7 @@ public:
 
     void Close();
 
-    unsigned char readNextByte();
+    std::optional<unsigned char> readNextByte();
 
 
 private:
diff --git a/src/core/streams/BitStream.h b/src/core/streams/BitStream.h
index 9dd3fc6..f73714f 100644
--- a/src/core/streams/BitStream.h
+++ b/src/core/streams/BitStream.h
@@ -27,6 +27,8 @@ public:
 
     virtual void writeByte(unsigned char data) = 0;
 
+    virtual void writeBytes(const std::vector<unsigned char> data) = 0;
+
 protected:
     int mByteOffset{0};
     unsigned mBitOffset{0};
diff --git a/src/core/streams/BufferBitStream.h b/src/core/streams/BufferBitStream.h
index bc898c4..1a3639c 100644
--- a/src/core/streams/BufferBitStream.h
+++ b/src/core/streams/BufferBitStream.h
@@ -17,6 +17,11 @@ public:
 
     void writeByte(unsigned char data) override;
 
+    void writeBytes(const std::vector<unsigned char> data) override
+    {
+        std::copy(data.begin(), data.end(), std::back_inserter(mBuffer));
+    }
+
     const std::vector<unsigned char>& getBuffer() const
     {
         return mBuffer;
diff --git a/src/core/streams/InputBitStream.h b/src/core/streams/InputBitStream.h
index 5831fe6..6b762d7 100644
--- a/src/core/streams/InputBitStream.h
+++ b/src/core/streams/InputBitStream.h
@@ -16,6 +16,11 @@ class InputBitStream : public BitStream
 
     void writeByte(unsigned char data) override;
 
+    void writeBytes(const std::vector<unsigned char> data) override
+    {
+
+    }
+
 private:
     std::basic_istream<unsigned char>* mStream{nullptr};
 };
diff --git a/src/core/streams/OutputBitStream.cpp b/src/core/streams/OutputBitStream.cpp
index 5e05194..5adf599 100644
--- a/src/core/streams/OutputBitStream.cpp
+++ b/src/core/streams/OutputBitStream.cpp
@@ -26,3 +26,11 @@ void OutputBitStream::writeByte(unsigned char data)
 {
     (*mStream) << data;
 }
+
+void OutputBitStream::writeBytes(const std::vector<unsigned char> data)
+{
+    for(auto byte : data)
+    {
+        writeByte(byte);
+    }
+}
diff --git a/src/core/streams/OutputBitStream.h b/src/core/streams/OutputBitStream.h
index 5dc59a1..1a119d5 100644
--- a/src/core/streams/OutputBitStream.h
+++ b/src/core/streams/OutputBitStream.h
@@ -17,6 +17,8 @@ public:
 
     void writeByte(unsigned char data) override;
 
+    void writeBytes(const std::vector<unsigned char> data) override;
+
 private:
     std::basic_ostream<char>* mStream{nullptr};
 };
diff --git a/src/image/ImageBitStream.h b/src/image/ImageBitStream.h
index 0663bd0..7a9324b 100644
--- a/src/image/ImageBitStream.h
+++ b/src/image/ImageBitStream.h
@@ -17,6 +17,11 @@ public:
 
     void writeByte(unsigned char data) override;
 
+    void writeBytes(const std::vector<unsigned char> data) override
+    {
+
+    }
+
 private:
     Image<unsigned char>* mImage{nullptr};
 };
diff --git a/src/image/PngElements.h b/src/image/PngElements.h
index 5125c80..d9612f1 100644
--- a/src/image/PngElements.h
+++ b/src/image/PngElements.h
@@ -1,5 +1,7 @@
 #pragma once
 
+#include "CyclicRedundancyChecker.h"
+
 #include <string>
 #include <sstream>
 
@@ -15,15 +17,23 @@ namespace Png
         return {13, 10, 26, 10};
     }
 
+    inline std::string getName()
+    {
+        return "PNG";
+    }
+
     struct IHDRChunk
     {
-        unsigned width{0};
-        unsigned height{0};
-        char bitDepth{0};
-        char colorType{0};
-        char compressionMethod{0};
-        char filterMethod{0};
-        char interlaceMethod{0};
+        uint32_t width{0};
+        uint32_t height{0};
+        unsigned char bitDepth{0};
+        unsigned char colorType{0};
+        unsigned char compressionMethod{0};
+        unsigned char filterMethod{0};
+        unsigned char interlaceMethod{0};
+        std::string name{"IHDR"};
+
+        std::vector<unsigned char> mData;
 
         std::string toString() const
         {
@@ -37,6 +47,42 @@ namespace Png
             sstr << "interlaceMethod: " << (int)interlaceMethod << "\n";
             return sstr.str();
         }
+
+        uint32_t getLength() const
+        {
+            return 13;
+        }
+
+        void updateData()
+        {
+            mData.clear();
+            unsigned num_bytes = sizeof(uint32_t);
+
+            for(unsigned idx=0; idx<num_bytes;idx++)
+            {
+                mData.push_back(ByteUtils::getByteN(width, idx));
+            }
+
+            for(unsigned idx=0; idx<num_bytes;idx++)
+            {
+                mData.push_back(ByteUtils::getByteN(height, idx));
+            }
+            mData.push_back(bitDepth);
+            mData.push_back(colorType);
+            mData.push_back(compressionMethod);
+            mData.push_back(filterMethod);
+            mData.push_back(interlaceMethod);
+        }
+
+        uint32_t getCrc() const
+        {
+            CyclicRedundancyChecker crc_check;
+            std::vector<unsigned char> char_data = StringUtils::toBytes(name);
+            std::copy(mData.begin(), mData.end(), std::back_inserter(char_data));
+
+            auto result = crc_check.doCrc(char_data.data(), char_data.size());
+            return result;
+        }
     };
 }
 
diff --git a/src/image/PngReader.cpp b/src/image/PngReader.cpp
index 77fefe0..5050c0d 100644
--- a/src/image/PngReader.cpp
+++ b/src/image/PngReader.cpp
@@ -88,11 +88,11 @@ void PngReader::readIDATChunk(unsigned length)
 {
     if (mAwaitingDataBlock)
     {
-        mEncoder->setCompressionMethod(mFile->readNextByte());
-        mEncoder->setExtraFlags(mFile->readNextByte());
+        mEncoder->setCompressionMethod(*mFile->readNextByte());
+        mEncoder->setExtraFlags(*mFile->readNextByte());
         for(unsigned idx=0; idx<length-2; idx++)
         {
-            mInputStream->writeByte(mFile->readNextByte());
+            mInputStream->writeByte(*mFile->readNextByte());
         }
         mAwaitingDataBlock = false;
     }
@@ -100,7 +100,7 @@ void PngReader::readIDATChunk(unsigned length)
     {
         for(unsigned idx=0; idx<length; idx++)
         {
-            mInputStream->writeByte(mFile->readNextByte());
+            mInputStream->writeByte(*mFile->readNextByte());
         }
     }
 }
diff --git a/src/image/PngWriter.cpp b/src/image/PngWriter.cpp
index 3064021..73a3384 100644
--- a/src/image/PngWriter.cpp
+++ b/src/image/PngWriter.cpp
@@ -9,6 +9,8 @@
 
 #include "Lz77Encoder.h"
 
+#include "ByteUtils.h"
+
 #include <stdio.h>
 
 PngWriter::PngWriter()
@@ -34,15 +36,49 @@ void PngWriter::setPath(const Path& path)
 void PngWriter::writeSignature()
 {
     mOutStream->writeByte(Png::getHighBitCheck());
-    for (auto byte : Png::getSignature())
-    {
-        mOutStream->writeByte(byte);
-    }
+    mOutStream->writeBytes(StringUtils::toBytes(Png::getName()));
+    mOutStream->writeBytes(Png::getSignature());
 }
 
 void PngWriter::writeHeader()
 {
     writeSignature();
+
+    Png::IHDRChunk header_chunk;
+    header_chunk.width = mWorkingImage->getWidth();
+    header_chunk.height = mWorkingImage->getHeight();
+    header_chunk.bitDepth = mWorkingImage->getBitDepth();
+    header_chunk.colorType = 6;
+
+    auto length = header_chunk.getLength();
+    auto crc = header_chunk.getCrc();
+
+    unsigned num_bytes = sizeof(uint32_t);
+    for(unsigned idx=0; idx<num_bytes;idx++)
+    {
+        mOutStream->writeByte(ByteUtils::getByteN(length, idx));
+    }
+    mOutStream->writeBytes(StringUtils::toBytes(header_chunk.name));
+
+    for(unsigned idx=0; idx<num_bytes;idx++)
+    {
+        mOutStream->writeByte(ByteUtils::getByteN(header_chunk.width, idx));
+    }
+
+    for(unsigned idx=0; idx<num_bytes;idx++)
+    {
+        mOutStream->writeByte(ByteUtils::getByteN(header_chunk.height, idx));
+    }
+    mOutStream->writeByte(header_chunk.bitDepth);
+    mOutStream->writeByte(header_chunk.colorType);
+    mOutStream->writeByte(header_chunk.compressionMethod);
+    mOutStream->writeByte(header_chunk.filterMethod);
+    mOutStream->writeByte(header_chunk.interlaceMethod);
+
+    for(unsigned idx=0; idx<num_bytes;idx++)
+    {
+        mOutStream->writeByte(ByteUtils::getByteN(crc, idx));
+    }
 }
 
 void PngWriter::write(const std::unique_ptr<Image<unsigned char> >& image)
@@ -50,6 +86,7 @@ void PngWriter::write(const std::unique_ptr<Image<unsigned char> >& image)
     if (!mPath.empty())
     {
         mWorkingFile = std::make_unique<File>(mPath);
+        mWorkingFile->SetAccessMode(File::AccessMode::Write);
         mWorkingFile->Open(true);
         mOutStream = std::make_unique<OutputBitStream>(mWorkingFile->GetOutHandle());
     }
diff --git a/src/image/PngWriter.h b/src/image/PngWriter.h
index b8e8656..db96936 100644
--- a/src/image/PngWriter.h
+++ b/src/image/PngWriter.h
@@ -27,6 +27,7 @@ private:
     void writeSignature();
     void writeHeader();
 
+    //void writeIDatChunk();
 
     Path mPath;
     Image<unsigned char>* mWorkingImage{nullptr};
diff --git a/test/core/TestByteUtils.cpp b/test/core/TestByteUtils.cpp
index ae88e84..6b545a7 100644
--- a/test/core/TestByteUtils.cpp
+++ b/test/core/TestByteUtils.cpp
@@ -13,6 +13,16 @@ int main()
     auto slice = ByteUtils::getMBitsAtN(byte, 3, 3);
     std::cout << "Slice is " << ByteUtils::toString(slice) << std::endl;
 
+    uint32_t input {12345678};
+    auto byte0 = ByteUtils::getByteN(input, 0);
+    auto byte1 = ByteUtils::getByteN(input, 1);
+    auto byte2 = ByteUtils::getByteN(input, 2);
+    auto byte3 = ByteUtils::getByteN(input, 3);
+
+    std::cout << "Byte0 is " << ByteUtils::toString(byte0) << std::endl;
+    std::cout << "Byte1 is " << ByteUtils::toString(byte1) << std::endl;
+    std::cout << "Byte2 is " << ByteUtils::toString(byte2) << std::endl;
+    std::cout << "Byte3 is " << ByteUtils::toString(byte3) << std::endl;
 
     return 0;
 }
diff --git a/test/image/TestPngWriter.cpp b/test/image/TestPngWriter.cpp
index 26c6549..b6df3c5 100644
--- a/test/image/TestPngWriter.cpp
+++ b/test/image/TestPngWriter.cpp
@@ -1,7 +1,7 @@
 #include "Image.h"
 #include "PngWriter.h"
 
-
+#include "File.h"
 #include "BitStream.h"
 #include "ImagePrimitives.h"
 
@@ -24,5 +24,15 @@ int main()
     writer.setPath("test.png");
     writer.write(image);
 
+    File test_file("test.png");
+    test_file.SetAccessMode(File::AccessMode::Read);
+    test_file.Open(true);
+
+    while(auto byte = test_file.readNextByte())
+    {
+        std::cout << static_cast<unsigned>(*byte) << std::endl;
+    }
+    test_file.Close();
+
     return 0;
 }