Color to Black & White

[amitabh]

How do I change a bitmap being displayed from color to Black & white ?

[Megatron]

Not too sure on this, but I think you have to add the red, green and blue values together, and take the average of them (by diving them by 3).

[Megatron]

Private Declare Function SetPixel Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, ByVal crColor As Long) As Long
Private Declare Function GetPixel Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long) As Long

Private Sub Command1_Click()

For x = 0 To Picture2.Width / Screen.TwipsPerPixelX
For y = 0 To Picture2.Height / Screen.TwipsPerPixelY
DoEvents
lColor = GetPixel(Picture2.hdc, x, y)
lRed = lColor Mod &H100
lGreen = Int(lColor / &H100) Mod &H100
lBlue = Int(lColor / &H10000) Mod &H100
t = Abs(Int((lRed + lGreen + lBlue) / 3))
SetPixel hdc, x, y, RGB(t, t, t)
Next y
Next x

End Sub

[amitabh]

Thanks Megatron.
Btw, if you are working in Win 2000, you can use SetColorAdjustment to get a negative. You can even increase or decrease the brightness, gamma levels etc

[Dirk]

How to then save this as a black and white bitmap?

TIA

[Sastraxi]

I think VBEMPIRE has the right values, it's not just / 3.

[jim mcnamara]

the CCIR recomended use for RGB -> monochrome conversion is luminance for use on monochrome monitors.

Y = 0.299*R + 0.587*G + 0.114*B

color = RGB(Y,Y,Y)