Adding wave to Z wave in image plot

Function/wave AddTwoWave(w1,w2,flag)
    wave w1   //the original image
    wave w2   //the image to be added
    Variable flag //0:create new wave, named by w_tmp; 1:overwrite w1
   
    Variable x0,dx,nx,y0,dy,ny
    [x0,dx,nx]=GetWavesRangeMax(w1,w2,0)
    [y0,dy,ny]=GetWavesRangeMax(w1,w2,1)
   
    Make/O/N=(nx,ny) w_tmp
    SetScale/P x,x0,dx,w_tmp
    SetScale/P y,y0,dy,w_tmp
    w_tmp=GetInterp2dValue(w1,x,y)+GetInterp2dValue(w2,x,y)
    if(0==flag)
        return w_tmp
    else
        Duplicate/O w_tmp w1
        Killwaves/Z w_tmp
        return w1
    endif  
End
Function [Variable v0,Variable d,Variable n]GetWavesRangeMax(wave w1,wave w2,Variable dim)
    Variable vmin1,d1,vmax1,vmin2,d2,vmax2
    [vmin1,d1,vmax1]=GetScaleInfo(w1,dim)
    [vmin2,d2,vmax2]=GetScaleInfo(w2,dim)
    v0=min(vmin1,vmin2)
    d=min(d1,d2)
    n=floor((max(vmax1,vmax2)-v0)/d)+1
End
Function [Variable v0,Variable d,Variable v1] GetScaleInfo(wave w,variable dim)
    v0=dimoffset(w,dim)
    d=dimdelta(w,dim)
    v1=v0+(dimsize(w,dim)-1)*d
End
Function GetInterp2dValue(w,x,y) //if (x,y) is out scale index range, return 0
    wave w                        //else,return interpolated value
    variable x,y
    Variable v0=interp2d(w,x,y)
    if(2==numtype(v0))
        return 0
    endif
    return v0
end