Member Avatar for tripes

i am working on a project in vb.net 2003 and i want to get the color of a pixel when i click on the image loaded in the picturebox. i ve tried anything but nothing seems to work.... help please
:'(

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  • Latest Post Latest Post by Teme64

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Short clarifier and a robust fix that complements @Tempe64's answer and addresses the common reasons a click-read can "fail" for : most problems are not GetPixel itself but coordinate mapping (PictureBox SizeMode), bitmap lifetime/format, and performance when reading many pixels.

When the PictureBox scales or centers the image (SizeMode = StretchImage, Zoom, CenterImage) the mouse coordinates (e.X, e.Y) are control coordinates, not image pixel coordinates. Map the control point to the image point before calling GetPixel. For Zoom you must compute the scale as Min(pictureboxWidth/imageWidth, pictureboxHeight/imageHeight), find the scaled image rectangle inside the control, subtract the offsets, then divide by the scale. Always validate the mapped point is inside the image bounds.

A compact VB example that performs the mapping and safely reads a pixel (works whether PictureBox.Image is already a Bitmap or not):

Private Function ControlToImagePoint(pb As PictureBox, p As Point) As Point?
    If pb.Image Is Nothing Then Return Nothing
    Dim imgW = pb.Image.Width, imgH = pb.Image.Height
    Dim pbW = pb.ClientSize.Width, pbH = pb.ClientSize.Height
    Dim ix As Integer, iy As Integer

    Select Case pb.SizeMode
        Case PictureBoxSizeMode.Normal, PictureBoxSizeMode.AutoSize
            ix = p.X : iy = p.Y
        Case PictureBoxSizeMode.CenterImage
            Dim offX = (pbW - imgW) \ 2, offY = (pbH - imgH) \ 2
            ix = p.X - offX : iy = p.Y - offY
        Case PictureBoxSizeMode.StretchImage
            ix = CInt(p.X * (CDbl(imgW) / pbW)) : iy = CInt(p.Y * (CDbl(imgH) / pbH))
        Case PictureBoxSizeMode.Zoom
            Dim ratio = Math.Min(CDbl(pbW) / imgW, CDbl(pbH) / imgH)
            Dim scaledW = CInt(imgW * ratio), scaledH = CInt(imgH * ratio)
            Dim offX = (pbW - scaledW) \ 2, offY = (pbH - scaledH) \ 2
            ix = CInt((p.X - offX) / ratio) : iy = CInt((p.Y - offY) / ratio)
        Case Else
            ix = p.X : iy = p.Y
    End Select

    If ix < 0 Or iy < 0 Or ix >= imgW Or iy >= imgH Then Return Nothing
    Return New Point(ix, iy)
End Function

Usage notes: in the click handler map the point, then read color. If PictureBox.Image is not a Bitmap, create a temporary Bitmap inside a Using block so it is disposed. For many pixel reads, GetPixel is slow — use LockBits and work on the raw buffer instead. Also be aware of indexed pixel formats; clone to a 24bpp/32bpp format before reading if colors look wrong.

Member Avatar for Teme64

This is for VB.NET 2005 and I hope it works in 2003 too

Private Sub PictureBox1_MouseClick(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseClick
  '
  Dim TempBitmap As New Bitmap(PictureBox1.Image)
  Dim MyColor As Color

  MyColor = TempBitmap.GetPixel(e.X, e.Y)
  MessageBox.Show("Pixel x=" & e.X & ", y=" & e.Y & ", color=" & MyColor.ToString, "Color", MessageBoxButtons.OK, MessageBoxIcon.Information)

End Sub

Make sure that an image is loaded to picturebox before mouse click.

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