FUNCTION Rgb2Gray ALIAS "Rgb2Gray" (BYVAL RGBValue AS DWORD) EXPORT AS DWORD

'// Red? = (RGBValue AND &H000000FF???) * .3
'// SHIFT RIGHT colorRGB???, 8
'// Green? = (RGBValue AND &H000000FF???) * .59
'// SHIFT RIGHT colorRGB???, 8
'// Blue? = (RGBValue AND &H000000FF???) * .11
'// Gray? = Red? + Green? + Blue?
'// FUNCTION = RGB(Gray?, Gray?, Gray?)

'// IF RGBValue = %ZD_TRANSCOLOR THEN FUNCTION = RGBValue: EXIT FUNCTION

#REGISTER NONE

!XOR ESI, ESI
!XOR EDX, EDX
!MOV ECX, RGBValue

' Red
!MOV EAX, 19595
!MOV DL, CL
!MUL EDX
!Add ESI, EAX

' Green
!MOV EAX, 38470
!SHR ECX, 8
!MOV DL, CL
!MUL EDX
!Add ESI, EAX

' Blue
!MOV EAX, 7471
!SHR ECX, 8
!MOV DL, CL
!MUL EDX
!Add ESI, EAX

!SHR ESI, 16
!MOV EDX, ESI

' Put Gray Value to a DWORD (0GGG)
!XOR EAX, EAX
!OR AL, DL
!SHL EAX, 8
!OR AL, DL
!SHL EAX, 8
!OR AL, DL

!MOV FUNCTION, EAX

END FUNCTION