Question GIF Decoder

[lespaul36]

I am having trouble with a GIF Decoder that I am writing for vb.net 2003. I am using a 600 x 400 256 color image to test it. It gets about 1/4 way through then reads a end code. Any Idea what I am missing?

I use the routine bellow. I take all the bytes from the image data block and convert them to bits then process them. I have it work fine with a small 10 x 10 image, but it only has 4 colors.

Private Function GetIndexes(ByVal arrBits As ArrayList, ByVal MinimumCodeSize As Byte, ByVal ColorTable() As ColorTable) As ArrayList
        Dim pbytCount As Byte = MinimumCodeSize + 1
        Dim pshrtEndOfCode = CShort((2 ^ MinimumCodeSize) + 1)
        Dim pshrtReinit As Short = CShort(2 ^ MinimumCodeSize)
        Dim colCodeTree As New CodeIndexCollection 'The Code Tree
        Dim code As New CodeIndex 'the current code
        Dim CodeLast As CodeIndex  'the last code
        Dim pshrtCodeIndex As Short
        Dim pintLastRead As Integer = 0 'keep track of bits read
        Dim arCodeIndexStream As New ArrayList 'holds the actual color indexes
        Dim pintTotalBits As Integer = arrBits.Count - 1
        Dim pblnFirstCode As Boolean = True

        Do Until pintLastRead = pintTotalBits
            pshrtCodeIndex = Me.GetValue(arrBits, pintLastRead, pbytCount - 1)
            pintLastRead += pbytCount
            If pshrtCodeIndex = pshrtEndOfCode Then 'DONE
                Exit Do
            ElseIf pshrtCodeIndex = pshrtReinit Then 'ReInit
                colCodeTree.Clear()
                pbytCount = MinimumCodeSize + 1
                colCodeTree = InitCodeTable(ColorTable)
                pblnFirstCode = True
                GoTo reinit
            Else
                'process code
                'Check for code
                Dim findcode As CodeIndex = colCodeTree.FindByIndex(pshrtCodeIndex)
                If pblnFirstCode Then
                    arCodeIndexStream.Add(pshrtCodeIndex)
                    Dim arVals As New ArrayList
                    arvals.Add(pshrtCodeIndex)
                    code = New CodeIndex(pshrtCodeIndex, arvals)
                    CodeLast = code
                    pblnFirstCode = False
                    GoTo reinit
                End If
                If findcode Is Nothing Then 'no code found
                    'get first color index of last codeindex
                    Dim pintLastColorIndex As Integer = CodeLast.Values(0)
                    Dim arVals As New ArrayList
                    arVals.AddRange(CodeLast.Values)
                    arVals.Add(pintLastColorIndex)
                    code = New CodeIndex(colCodeTree.Count, arVals)
                    arCodeIndexStream.AddRange(code.Values)
                    colCodeTree.Add(code)
                    'get more bits next time?
                    If code.Index = (2 ^ pbytCount) - 1 Then
                        pbytCount += 1
                    End If
                    CodeLast = code
                Else 'Code Found
                    arCodeIndexStream.AddRange(findcode.Values)
                    Dim pintNewColorIndex As Integer = findcode.Values(0)
                    Dim arVals As New ArrayList
                    arVals.AddRange(CodeLast.Values)
                    arVals.Add(pintNewColorIndex)
                    code = New CodeIndex(colCodeTree.Count, arVals)
                    colCodeTree.Add(code)
                    'get more bits next time?
                    If code.Index = (2 ^ pbytCount) - 1 Then
                        pbytCount += 1
                    End If
                    CodeLast = findcode
                End If

            End If

ReInit:
        Loop

        Return arCodeIndexStream
    End Function