Color Matrix Alpha values and drawing images.

Question

Hi All,
I am experimenting with using a color matrix to change images and have brightness, R, G, B changing but the alpha does not seem to do anything. I have a scrollbar for the alpha value in the matrix in the example. It seems it should change the image in some
way but it does not.
In this example I put 1 for red in the matrix thinking as I moved the scroll bar the alpha transparency would change the image in some way but it does not? It does not matter what colors or image I use nothing seems to happen with alpha? Is it
only for drawing lines and such or does it do something to images? If so what?
Imports System.Drawing.Imaging
Public Class Form3
Private rustybmp As New Bitmap("c:\bitmaps\rusty.jpg")
Private Sub Form3_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Me.DoubleBuffered = True
VScrollBar1.Maximum = 100
VScrollBar1.Minimum = 0
VScrollBar1.Value = 50
End Sub
Private Sub Form3_Paint(sender As Object, e As PaintEventArgs) Handles Me.Paint
Dim cm As ColorMatrix = New ColorMatrix(New Single()() _
{New Single() {1, 0.0, 0.0, 0.0, 0.0}, _
New Single() {0.0, 1, 0.0, 0.0, 0.0}, _
New Single() {0.0, 0.0, 1, 0.0, 0.0}, _
New Single() {0.0, 0.0, 0.0, 1.0, 0.0}, _
New Single() {1, 0, 0, VScrollBar1.Value / 100, 1}})
Dim image_attr As New ImageAttributes
image_attr.SetColorMatrix(cm)
e.Graphics.DrawImage(rustybmp, Me.ClientRectangle, 0, 0, rustybmp.Width, rustybmp.Height, GraphicsUnit.Pixel, image_attr)
End Sub
Private Sub VScrollBar1_Scroll(sender As Object, e As ScrollEventArgs) Handles VScrollBar1.Scroll
Me.Refresh()
End Sub
End Class

Answer 1

I didn't try this.
How to: Use a Color Matrix to Set Alpha Values in Images
La vida loca
Oh, ok, in your link example the alpha is the 4 row 4 col.
I was using the 5th row 4th col because I thought that was R, G, B A across the 5th row. Maybe that is for a solid brush or something.
This works as I expected that way. Still looking....
Dim cm As ColorMatrix = New ColorMatrix(New Single()() _
{New Single() {1, 0.0, 0.0, 0.0, 0.0}, _
New Single() {0.0, 1, 0.0, 0.0, 0.0}, _
New Single() {0.0, 0.0, 1, 0.0, 0.0}, _
New Single() {0.0, 0.0, 0.0, VScrollBar1.Value / 100, 0.0}, _
New Single() {0, 0, 0, 0, 1}})
Cool!
Now if you could just get that working with HoloLens..... :)
La vida loca