What is the "W" in this RGBAW color space matrix

[Joachim-Otahal]

Type of issue

Missing information

Description

That article helped me a lot to massively speed up an image invert and color change in powershell.
But what is the "W" in the color space here? I tried to find anything, but all search results link back to this article.

Page URL

https://learn.microsoft.com/en-us/dotnet/api/system.drawing.imaging.colormatrix?view=windowsdesktop-9.0

Content source URL

https://github.com/dotnet/dotnet-api-docs/blob/main/xml/System.Drawing.Imaging/ColorMatrix.xml

Document Version Independent Id

965b4c7a-083d-b594-f75d-e4f63b71e2e0

Article author

@dotnet-bot

[gfoidl]

White.

[Joachim-Otahal]

White.

Thank you for your response in the 24th of December! I suspected too, but...
How or when is it applied? I changed the fifth value to 0, 0.5, 1, 1000, -1000 in each row. And the outcome is no different, pixel exact the same transformation as the rest of that colormatrix says.
Is it applied only when a specific colorspace is used? The source and destination picture it is applied to is: [System.Drawing.Imaging.PixelFormat]::Format24bppRgb. Or is there something else how this value is used?

The whole powershell code used is this, to invert a white background diagram into dark color scheme and then gamma up the lower values to be better visible as a non-intrusive regularly updated windows wallpaper. $bmp is the original to be transformed. (Code to update the currently shown wallpaper is left out)

# https://learn.microsoft.com/en-us/dotnet/api/system.drawing.imaging.colormatrix
$ColorMatrix = [System.Drawing.Imaging.ColorMatrix]::new( [float[][]] @(
        [float[]](-0.2, 0, 0, 0, 0), # Invert R
        [float[]](0, -0.2, 0, 0, 0), # Invert G
        [float[]](0, 0, -0.2, 0, 0), # Invert B
        [float[]](0, 0, 0, 1, 0),  # Alpha: Do nothing
        [float[]](0.2, 0.2, 0.2, 0, 1)   # Translate/Offset RGBA
    )
)
# https://learn.microsoft.com/en-us/dotnet/api/system.drawing.imaging.imageattributes
$ImageAttributes = [System.Drawing.Imaging.ImageAttributes]::new()
$ImageAttributes.SetColorMatrix($ColorMatrix)
# https://learn.microsoft.com/en-us/dotnet/api/system.drawing.imaging.imageattributes.setgamma
$ImageAttributes.SetGamma(0.6)
$bmpinv = [System.Drawing.Bitmap]::new($bmp.Width,$bmp.Height,[System.Drawing.Imaging.PixelFormat]::Format24bppRgb)
$pictinv = [System.Drawing.Graphics]::FromImage($bmpinv)
$pictinv.DrawImage($bmp, # Source image
    [System.Drawing.Rectangle]::new(0,0,$bmp.Width,$bmp.Height), # Destination rectangle, here same as source
    0,0,$bmp.Width,$bmp.Height, # Source rectangle.
    [System.Drawing.GraphicsUnit]::Pixel, # We want 1:1 not inch or whatever
    $ImageAttributes # Finally the matrix
)
$bmpinv.Save("$DataBaseDir\today-inv.png",[System.Drawing.Imaging.ImageFormat]::Png)
$pictinv.Dispose()
$bmpinv.Dispose()