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| Title | Use an ImageAttributes object to adjust an image's brightness in Visual Basic .NET |
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| Description | This example shows how to use an ImageAttributes object to adjust an image's brightness in Visual Basic .NET |
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| Keywords | color, color components, brightness, ColorMatrix, ImageAttributes, VB .NET |
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| Categories | VB.NET, Graphics |
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When transforming colors, Visual Basic .NET represents a color using a vector with 5 entries: red, green, blue, alhpa (opacity), and a scaling value that is 1. A ColorMatrix can transform an image's colors by multiplying each pixel's color vector by a 5-by-5 matrix. An identity matrix, with 1's down the diagonal, leaves all colors unchanged.
The following code uses a ColorMatrix to adjust the brightness of an image's pixels. (To see how this works, multiply the first matrix by the vector (r, g, b, a, 1) and notice that the result is (brt * r, brt * g, brt * b, a, 1) so the red, green, and blue values have been scaled by a factor of brt.)
When you change the program's scroll bar or enter a new value in the TextBox, the program uses this routine to adjust the image's brightness accordingly.
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Private Sub picResult_Paint(ByVal sender As Object, ByVal e _
As System.Windows.Forms.PaintEventArgs) Handles _
picResult.Paint
Dim brt As Single = hbarBrightness.Value / 100
Dim image_attr As New ImageAttributes
Dim cm As ColorMatrix = New ColorMatrix(New Single()() _
{ _
New Single() {brt, 0.0, 0.0, 0.0, 0.0}, _
New Single() {0.0, brt, 0.0, 0.0, 0.0}, _
New Single() {0.0, 0.0, brt, 0.0, 0.0}, _
New Single() {0.0, 0.0, 0.0, 1.0, 0.0}, _
New Single() {0.0, 0.0, 0.0, 0.0, 1.0}})
Debug.WriteLine(brt)
Dim rect As Rectangle = _
Rectangle.Round(picSource.Image.GetBounds(GraphicsUnit.Pixel))
Dim wid As Integer = picSource.Image.Width
Dim hgt As Integer = picSource.Image.Height
image_attr.SetColorMatrix(cm)
e.Graphics.DrawImage(picSource.Image, rect, 0, 0, wid, _
hgt, GraphicsUnit.Pixel, image_attr)
End Sub
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This method is extremely fast so you can easily adjust brightness in real time.
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