How to access pixel data using the RawBlocks object

public static void ReadWriteRawBlocks(IRasterDataset rasDs)
{
    IRasterBandCollection rasBandCol = (IRasterBandCollection)rasDs;
    IRawBlocks rawBlocks;
    IRasterInfo rasInfo;
    IPixelBlock pb;

    // Iterate through each band of the dataset.
    for (int m = 0; m <= rasBandCol.Count - 1; m++)
    {
        // QI to IRawBlocks from IRasterBandCollection.
        rawBlocks = (IRawBlocks)rasBandCol.Item(m);
        rasInfo = rawBlocks.RasterInfo;
        // Create the pixel block.
        pb = rawBlocks.CreatePixelBlock();

        // Determine the tiling scheme for the raster dataset.

        int bStartX = (int)Math.Floor((rasInfo.Extent.Envelope.XMin -
            rasInfo.Origin.X) / (rasInfo.BlockWidth * rasInfo.CellSize.X));
        int bEndX = (int)Math.Ceiling((rasInfo.Extent.Envelope.XMax -
            rasInfo.Origin.X) / (rasInfo.BlockWidth * rasInfo.CellSize.X));
        int bStartY = (int)Math.Floor((rasInfo.Origin.Y -
            rasInfo.Extent.Envelope.YMax) / (rasInfo.BlockHeight *
            rasInfo.CellSize.Y));
        int bEndY = (int)Math.Ceiling((rasInfo.Origin.Y -
            rasInfo.Extent.Envelope.YMin) / (rasInfo.BlockHeight *
            rasInfo.CellSize.Y));

        // Iterate through the pixel blocks.
        for (int pbYcursor = startY; pbYcursor < endY; pbYcursor++)
        {
            for (int pbXcursor = startX; pbXcursor < endX; pbXcursor++)
            {
                // Get the pixel block.
                rawBlocks.ReadBlock(pbXcursor, pbYcursor, 0, pb);
                System.Array safeArray;
                // Put the pixel block into a SafeArray for manipulation.
                safeArray = (System.Array)pb.get_SafeArray(0);

                // Iterate through the pixels in the pixel block.
                for (int safeArrayHeight = 0; safeArrayHeight < pb.Height;
                    safeArrayHeight++)
                {
                    for (int safeArrayWidth = 0; safeArrayWidth < pb.Width;
                        safeArrayWidth++)
                    {
                        // Use System.Array.SetValue to write the new pixel value back into the SafeArray.
                        safeArray.SetValue(Convert.ToByte(128), safeArrayWidth,
                            safeArrayHeight);
                    }
                }
                // Set the SafeArray back to the pixel block.
                pb.set_SafeArray(0, safeArray);

                // Write the pixel block back to the dataset.
                rawBlocks.WriteBlock(pbXcursor, pbYcursor, 0, pb);
            }
        }
    }
}

Public Sub ReadWriteRawBlocks(ByVal rasDs As IRasterDataset)
    Dim rasBandCol As IRasterBandCollection
    rasBandCol = rasDs
    Dim rawBlocks As IRawBlocks
    Dim rasInfo As IRasterInfo
    Dim pb As IPixelBlock
    ' Iterate through each band of the dataset.
    For m = 0 To rasBandCol.Count - 1
        ' QI to IRawBlocks from IRasterBandCollection.
        rawBlocks = rasBandCol.Item(m)
        rasInfo = rawBlocks.RasterInfo
        ' Create the pixel block.
        pb = rawBlocks.CreatePixelBlock
        ' Determine the tiling scheme for the raster dataset.
        Dim startX, startY, endX, endY As Integer
        
        Dim bStartX As Integer = CInt(Math.Floor((rasInfo.Extent.Envelope.XMin - rasInfo.Origin.X) / _
                                 (rasInfo.BlockWidth * rasInfo.CellSize.X)))
        Dim bEndX As Integer = CInt(Math.Ceiling((rasInfo.Extent.Envelope.XMax - rasInfo.Origin.X) / _
                               (rasInfo.BlockWidth * rasInfo.CellSize.X)))
        Dim bStartY As Integer = CInt(Math.Floor((rasInfo.Origin.Y - rasInfo.Extent.Envelope.YMax) / _
                                 (rasInfo.BlockHeight * rasInfo.CellSize.Y)))
        Dim bEndY As Integer = CInt(Math.Ceiling((rasInfo.Origin.Y - rasInfo.Extent.Envelope.YMin) / _
                               (rasInfo.BlockHeight * rasInfo.CellSize.Y)))
        
        ' Iterate through the pixel blocks.
        For pbYcursor = startY To endY - 1
            For pbXcursor = startX To endX - 1
                ' Get the pixel block.
                rawBlocks.ReadBlock(pbXcursor, pbYcursor, 0, pb)
                Dim safeArray As System.Array
                ' Put the pixel block into a SafeArray for manipulation.
                safeArray = pb.SafeArray(0)
                ' Iterate through the pixels in the pixel block.
                For safeArrayHeight = 0 To pb.Height
                    For safeArrayWidth = 0 To pb.Width
                        ' Use System.Array.SetValue to write the new pixel value (128) back into the SafeArray.
                        safeArray.SetValue(CType(128, Byte), safeArrayWidth, safeArrayHeight)
                    Next
                Next
                ' Set the SafeArray back to the pixel block.
                pb.SafeArray(0) = safeArray
                ' Write the pixel block back to the dataset.
                rawBlocks.WriteBlock(pbXcursor, pbYcursor, 0, pb)
            Next
        Next
    Next
End Sub