MixImages function help

I've tried to make something like what you said:

Dim c1(Screen_Width-1,Screen_Height-1) 
Dim c2(Screen_Width-1,Screen_Height-1) 
Dim cm(Screen_Width-1,Screen_Height-1) 

Function MixImages(mix,ima1,ima2)

	buf1=ImageBuffer(ima1)
	buf2=ImageBuffer(ima2)
	bufm=ImageBuffer(mix)

	LockBuffer buf1
	LockBuffer buf2
	LockBuffer bufm
	
	For y=0 To Screen_Height-1
		For x=0 To Screen_Width-1
			c1(x,y)=ReadPixelFast(x,y,buf1)
			c2(x,y)=ReadPixelFast(x,y,buf2)
		Next
	Next
	
	For y=0 To Screen_Height-1
		For x=0 To Screen_Width-1
			red1=GetRed(c1(x,y))     :  red2=GetRed(c2(x,y))
			green1=GetGreen(c1(x,y)) :  green2=GetGreen(c2(x,y))
			blue1=GetBlue(c1(x,y))   :  blue2=GetBlue(c2(x,y))
			
			rm=red1+red2 : If rm>255 Then rm=255
			gm=green1+green2 : If gm>255 Then gm=255
			bm=blue1+blue2 : If bm>255 Then bm=255
			
			cm(x,y)=Combine(rm,gm,bm)
		Next
	Next

	For y=0 To Screen_Height-1
		For x=0 To Screen_Width-1
			WritePixelFast x,y,cm(x,y),bufm
		Next
	Next

	UnlockBuffer bufm
	UnlockBuffer buf2
	UnlockBuffer buf1
	
End Function

But it is slower than what I wrote yesterday! I think that using all this arrays it isn't usefull.
Is the code similar to what you thought?

A last question: how can I wrote the codes in green in this forums? Thanks!