Before nothing, I'll note that I accept a C# or VB.Net solution.
I have this old code which I'm trying to refactor to avoid the bad habbits and performance inefficiency of using GetPixel/SetPixel methods:
<Extension>
Public Function ChangeColor(ByVal sender As Image,
ByVal oldColor As Color,
ByVal newColor As Color) As Image
Dim bmp As New Bitmap(sender.Width, sender.Height, sender.PixelFormat)
Dim x As Integer = 0
Dim y As Integer = 0
While (x < bmp.Width)
y = 0
While y < bmp.Height
If DirectCast(sender, Bitmap).GetPixel(x, y) = oldColor Then
bmp.SetPixel(x, y, newColor)
End If
Math.Max(Threading.Interlocked.Increment(y), y - 1)
End While
Math.Max(Threading.Interlocked.Increment(x), x - 1)
End While
Return bmp
End Function
So, after reading the most voted solution here using LockBits approach, I'm trying to adapt the code to my needs, to use a Color as parameter instead of a sequence of bytes (because in essence are the same):
<Extension>
Public Function ChangeColor(ByVal sender As Image,
ByVal oldColor As Color,
ByVal newColor As Color) As Image
Dim bmp As Bitmap = DirectCast(sender.Clone, Bitmap)
' Lock the bitmap's bits.
Dim rect As New Rectangle(0, 0, bmp.Width, bmp.Height)
Dim bmpData As BitmapData = bmp.LockBits(rect, ImageLockMode.ReadWrite, bmp.PixelFormat)
' Get the address of the first line.
Dim ptr As IntPtr = bmpData.Scan0
' Declare an array to hold the bytes of the bitmap.
Dim numBytes As Integer = (bmpData.Stride * bmp.Height)
Dim rgbValues As Byte() = New Byte(numBytes - 1) {}
' Copy the RGB values into the array.
Marshal.Copy(ptr, rgbValues, 0, numBytes)
' Manipulate the bitmap.
For i As Integer = 0 To rgbValues.Length - 1 Step 3
If (Color.FromArgb(rgbValues(i), rgbValues(i + 1), rgbValues(i + 2)) = oldColor) Then
rgbValues(i) = newColor.R
rgbValues(i + 1) = newColor.G
rgbValues(i + 2) = newColor.B
End If
Next i
' Copy the RGB values back to the bitmap.
Marshal.Copy(rgbValues, 0, ptr, numBytes)
' Unlock the bits.
bmp.UnlockBits(bmpData)
Return bmp
End Function
I have two problems with the extension method, firstlly is that if pixelformat is not Format24bppRgb as the original example then all goes wrong, an IndexOutOfRange exception is thrown in the loop, I suppose this is because I'm reading 3 bytes (RGB) instead of 4 (ARGB), but I'm not sure how to adapt it for any source pixelformat that I can pass to the function.
Secondlly is that If I use Format24bppRgb as the original C# example, the color changes to black.
Note that I'm not sure if the original solution given in the C# question that I linked is wrong, because as per their comments seems is wrong in some way.
This is the way I'm trying to use it:
' This function creates a bitmap of a solid color.
Dim srcImg As Bitmap = ImageUtil.CreateSolidcolorBitmap(New Size(256, 256), Color.Red)
Dim modImg As Image = srcImg.ChangeColor(Color.Red, Color.Blue)
PictureBox1.BackgroundImage = srcImg
PictureBox2.BackgroundImage = modImg
