Formula to convert RGB > CMYK

Hi all
I am trying to find a formula the can convert RGB to CMYK. I already have tried the below formulas and they seem to produce the correct results for what the authors say will be produced but the results are vastly different to what photoshop produces. So who is right??? Because all the formulas i have found all produce similar results as each other but adobe couldn't have got is that wrong. Could They???
Please help
ant

        i = 1
        intCyan = (255 - intRed) / 255
        If i > intCyan Then
            i = intCyan
        End If  
        intMagenta = (255 - intGreen) / 255
        If i > intMagenta Then
            i = intMagenta
        End If  
        intYellow = (255 - intBlue) / 255
        If i > intYellow Then
            i = intYellow
        End If  
        If i > 0 Then
           intBlack = i
        Else    
           intBlack = 0        
        End If  

and another is

        intCyan = 1 - ( intRed / 255 )
        intMagenta = 1 - ( intGreen / 255 )
        intYellow = 1 - ( intBlue / 255 )
        intBlack = 1

        If intCyan < intBlack Then
            intBlack = intCyan
        End If    
        if intMagenta < intBlack  Then  
            intBlack = intMagenta
        End If            
        if intYellow < intBlack  Then  
            intBlack = intYellow
        End If            

        intCyan =  ( intCyan - intBlack ) / ( 1 - intBlack )
        intMagenta =  ( intMagenta - intBlack ) / ( 1 - intBlack )
        intYellow = ( intYellow - intBlack ) / ( 1 - intBlack )