How do I get the color of a pixel at X,Y using vb.net

Question

Hey I am able to set the color of image via set Pixel Property but when i put condition getPixel then no error occurs but the programme stucks

i put the code below please check it give me the solution :

    Dim b As Bitmap = New Bitmap("D:\test.bmp")

' Make Image Indexed

        Dim nii As New Bitmap(b.Width, b.Height,
System.Drawing.Imaging.PixelFormat.Format32bppPArgb)
        For y As Integer = 0 To nii.Height - 1
            For x = 0 To nii.Width - 1
                Dim cw As New Color
                cw = Color.Black
                If nii.GetPixel(x, y) = cw Then
                    nii.SetPixel(x, y, Red)
                End If

            Next
        Next
        PictureBox1.Image = FromFile("D:\test.bmp")
        PictureBox2.Image = nii

If i removed getPixel then programme works but full image color is going to be red.

Answer 1

You need to compare the ARGB values of color

Dim cw As New Color
cw = Color.Black
dim curPixColor as Color = b.GetPixel(x, y)
If curPixColor.ToArgb = cw.ToArgb Then
    nii.SetPixel(x, y, Color.Red)
End If

Or you should use the Equality Operator

Dim cw As New Color
cw = Color.Black
dim curPixColor as Color = b.GetPixel(x, y)
If Color.op_Equality(curPixColor, cw) Then
    nii.SetPixel(x, y, Color.Red)
End If

Reference:http://msdn.microsoft.com/en-us/library/system.drawing.color.op_equality(v=vs.110).aspx

Edit: As you are getting pixel from a bmp there is no transparency supported. so your comparing color should be

cw = Color.FromArgb(0,0,0,0)

Edit2: you are reading pixed from nii you should be reading from b

dim curPixColor as Color = b.GetPixel(x, y)

full code should be something like (tested)

    Dim b As Bitmap = New Bitmap("D:\test.bmp")

    ' Make Image Indexed

    Dim nii As New Bitmap(b.Width, b.Height, System.Drawing.Imaging.PixelFormat.Format32bppPArgb)
    For y As Integer = 0 To nii.Height - 1
        For x = 0 To nii.Width - 1
            Dim cw As New Color
            cw = Color.Black
            Dim curPixColor As Color = b.GetPixel(x, y)
            If curPixColor.ToArgb() = cw.ToArgb() Then
                nii.SetPixel(x, y, Color.Red)
            Else
                nii.SetPixel(x, y, curPixColor)
            End If
        Next
    Next
    PictureBox1.Image = Image.FromFile("D:\test.bmp")
    PictureBox2.Image = nii

Answer 2

I had a similar problem, but comparing the RGB values worked. Thanks!

In fact, instead of too many variables, you can just do:

If b.GetPixel(x,y).ToArgb() = Color.Black.ToArgb() then......