Getting maximum quality export for InDesign images or graphics

I'm extracting the images from an InDesign file for an ePub. I'm doing the ePub creating independant of InDesign, however with images I'm trying to preserve some of the work done by people in the past in formatting the images.

What I'm finding is that the image is exported the same size as in the InDesign document, the problem with this is that if I zoom into the image it looks pixelated, whereas if I zoom into the original document it's not pixelated at all. Any suggestions on how to modify the following code to get a higher resolution export? While I appreciate that the image size is preserved, I'm wondering at what point in the export the image resolution is scaled down.

function getImages(){
    for(var i = 0; i<app.activeDocument.pages.length; i++){
        for(var j = 0; j<app.activeDocument.pages[i].allPageItems.length; j++){
            var pageItem = app.activeDocument.pages[i].allPageItems[j];
            if(pageItem.constructor.name.match(/pdf|image/i)){
                pageItem.exportFile(ExportFormat.PNG_FORMAT,File("~\\desktop\\epub2\\"+app.activeDocument.name.replace(".indd","")+"\\oebps\\images\\"+pageItem.itemLink.name.substring(0,pageItem.itemLink.name.indexOf("."))+".png"),false);
                }
            }
        }
    }