function changePic( srcOn, srcOff, srcSelected )
{
    var imgOn, imgOff;
    var selectedImg;
    
    this.turnOn = turnOn;
    this.turnOff = turnOff;
    this.turnSelected = turnSelected;
    
    this.selectedImg = "";
    this.imgOn = new Image();
    this.imgOn.src = srcOn;
    this.imgOff = new Image();
    this.imgOff.src = srcOff;
    this.imgSelected = new Image();
    this.imgSelected.src = srcSelected;
    this.clickImg = clickImg;
}

function turnOn( imgName )
{
    if ( document.images[ imgName ] )
    {
        if ( imgName != this.selectedImg )
        {
            document.images[ imgName ].src = this.imgOn.src;
        }
    }
}

function turnOff( imgName )
{
    if ( document.images[ imgName ] )
    {
        if ( imgName != this.selectedImg )
        {
            document.images[ imgName ].src = this.imgOff.src;
        }
    }
}

function turnSelected( imgName )
{
    if ( document.images[ imgName ] )
    {
        if ( imgName != this.selectedImg )
        {
            document.images[ imgName ].src = this.imgSelected.src;
            this.selectedImg = imgName;
        }
    }
}

function clickImg( imgName )
{
    if ( imgName != this.selectedImg )
    {
        var selectedOld = this.selectedImg;
        this.turnSelected( imgName );
        this.turnOff( selectedOld );
    }
}