根据另外两个位图为新的位图选择颜色

Question

我正在尝试创建一个基本的隐写术程序。 基本上，我将一张图片上传到两个picture boxes 。 我用它们两个创建了一个位图，并能够通过单击以下代码来更改第二个picture box的颜色：

Private Sub PictureBox1_MouseClick(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseClick
        Dim MyColor As Color
        Dim bm As Bitmap = Me.PictureBox1.Image
        Dim bm2 As Bitmap = Me.PictureBox2.Image
        MyColor = bm.GetPixel(e.X, e.Y)
        Dim g As Graphics = PictureBox2.CreateGraphics
        bm2.SetPixel(e.X, e.Y, Color.Black)
        PictureBox2.Image = bm2
        MessageBox.Show( _
            "Pixel x=" & e.X & ", y=" & e.Y & ", color=" & MyColor.ToString, _
            "Color", _
            MessageBoxButtons.OK, _
            MessageBoxIcon.Information)

    End Sub

这可以更改第二个位图的像素。 当存储像素时，我使用以下代码：

Private Sub SaveToArray_Click(sender As Object, e As EventArgs) Handles SaveToArray.Click
        Dim bm As Bitmap = Me.PictureBox1.Image
        Dim bm2 As Bitmap = Me.PictureBox2.Image

        ReDim ColorArray(bm.Size.Height - 1, bm.Size.Width - 1)
        ReDim colorarray2(bm2.Size.Height - 1, bm2.Size.Width - 1)
        Dim i, j, k As Integer

        For i = 0 To bm.Size.Height - 1
            For j = 0 To bm.Size.Width - 1
                ColorArray(i, j) = bm.GetPixel(j, i)
                colorarray2(i, j) = bm2.GetPixel(j, i)
            Next
        Next
    End Sub

上面的两个代码都可以正常工作。 问题是当我想比较位图中的两个数组时。 我想比较数组，对于每个相同颜色的像素，我希望像素颜色等于第三个数组的color.black。 如果像素颜色不匹配，我希望第三个数组的像素颜色等于color.white。 然后，我想采用该第三数组并绘制第三位图。 以下代码是我遇到的麻烦：

 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim i, j As Integer
        Dim bm As Bitmap = Me.PictureBox1.Image
        Dim bm2 As Bitmap = Me.PictureBox2.Image

        For i = 0 To bm.Size.Height - 1
            For j = 0 To bm.Size.Width - 1
                If ColorArray(i, j) = colorarray2(i, j) Then

                    checkarray(i, j) = Color.Black
                Else
                    checkarray(i, j) = Color.White

                End If
            Next
        Next
        Dim bm3 As Bitmap
        For i = 0 To bm.Size.Height - 1
            For j = 0 To bm.Size.Width - 1
                bm3.SetPixel(i, j, checkarray(i, j))
            Next
        Next
        PictureBox2.Image = bm3
    End Sub

我特别在以下方面遇到问题：

 For i = 0 To bm.Size.Height - 1
            For j = 0 To bm.Size.Width - 1
                If ColorArray(i, j) = colorarray2(i, j) Then

                    checkarray(i, j) = Color.Black
                Else
                    checkarray(i, j) = Color.White

                End If
            Next
        Next

我得到未处理的NullReferenceException和对象引用未设置为对象的实例。

任何帮助将不胜感激。 谢谢！

编辑：

我这样声明数组：

Dim ColorArray(,) As Color
    Dim colorarray2(,) As Color
    Dim checkarray(,) As Color

Answer 1

您应该设置检查数组的大小：

ReDim checkarray(bm.Size.Height - 1, bm.Size.Width - 1)

另外，由于尚未创建对象，因此您将遇到“ bm3”问题。 将其更改为：

Dim bm3 As Bitmap = new Bitmap(bm.Size.Width, bm.Size.Height)

编辑：
您还必须切换i和j：

更改：

bm3.SetPixel(i, j, checkarray(i, j))

至：

bm3.SetPixel(j, i, checkarray(i, j))

Answer 2

通过首先切换i和j的大部分并将问题中的最后一个代码块更改为此，我发现这要容易得多：

Dim i, j As Integer

        Dim bm As Bitmap = Me.PictureBox1.Image
        Dim bm2 As Bitmap = Me.PictureBox2.Image
        Dim bm3 As Bitmap = Me.PictureBox2.Image
        ReDim checkarray(bm.Size.Width - 1, bm.Size.Height - 1)
        For i = 0 To bm.Size.Height - 1
            For j = 0 To bm.Size.Width - 1
                If ColorArray(j, i) = colorarray2(j, i) Then

                    bm3.SetPixel(j, i, Color.Black)
                Else
                    bm3.SetPixel(j, i, Color.White)

                End If
            Next
        Next
        PictureBox2.Image = bm3