Полный ресайз бекграунда не зависимо от размеров окна браузера

function backgroundScale()
{
    var imageRatio       = 1.75;
    var windowHeight     = document.body.clientHeight;
    var windowWidth      = document.body.clientWidth;
    var windowScale      = windowWidth / windowHeight;
    var targetWidth      = windowHeight * imageRatio;
    var targetWidthFull  = windowWidth;
    var leftPos          = - (targetWidth - windowWidth) / 2;
    var leftPosFull      = 0;

    if (windowScale <= imageRatio)
    {
        $('.background img').attr("width", targetWidth);
        $('.background').css("left", leftPos);
    }
    else
    {
        $('.background img').attr("width", targetWidthFull);
        $('.background').css("left", leftPosFull);
    }
}

$(window).resize(function()
{
    var imageRatio       = 1.75;
    var windowHeight     = document.body.clientHeight;
    var windowWidth      = document.body.clientWidth;
    var windowScale      = windowWidth / windowHeight;
    var targetWidth      = windowHeight * imageRatio;
    var targetWidthFull  = windowWidth;
    var leftPos          = - (targetWidth - windowWidth) / 2;
    var leftPosFull      = 0;

    if (windowScale <= imageRatio)
    {
        $('.background img').attr("width", targetWidth);
        $('.background').css("left", leftPos);
    }
    else
    {
        $('.background img').attr("width", targetWidthFull);
        $('.background').css("left", leftPosFull);
    }
    
    mainBaseResize();
});


function mainBaseResize()
{
    if(($('body').height() >= 800) && ($('#mainBase').height() <= 500)){
        $('#mainBase').height($('body').height() - 445 + "px");
    }
}
  
$(document).ready(function(){
    backgroundScale();
    
    mainBaseResize();

});

<div class="background">
        <img src="23.jpg" width="100%" alt="Spencer Street Background Image" />
</div>