从扩展文件加载的图像看起来比它看起来要小

Question

我正在开发一款包含许多图片的应用。由于app限制（50MB），我移动到扩展文件的一些图像。在我将所有图像放入不同的文件夹之前，例如drawable-xhdpi，drawable-mdpi等。现在我以编程方式确定手机的dpi是什么，并相应地获取图像。以下是重要的代码：

    public String getFolder()
    {
        String folder = "";
        int dpi = res.getDisplayMetrics().densityDpi;

        int widthPixels = metrics.widthPixels;
        int heightPixels = metrics.heightPixels;

        float scaleFactor = metrics.density;
        float widthDp = widthPixels / scaleFactor;
        float heightDp = heightPixels / scaleFactor;

        float smallestWidth = Math.min(widthDp, heightDp);

        if (smallestWidth > 720 && dpi == DisplayMetrics.DENSITY_MEDIUM) {
            //Device is a 10" tablet
        } 
        else if (dpi == DisplayMetrics.DENSITY_XHIGH||dpi == DisplayMetrics.DENSITY_TV) {
            //Device is a 7" tablet
            //xhdpi
            folder = "drawable-xhdpi/";
        }
        else if((smallestWidth > 480 && dpi == DisplayMetrics.DENSITY_MEDIUM)|| dpi == DisplayMetrics.DENSITY_HIGH)
        {
            //hdpi
            folder = "drawable-hdpi/";

        }
        else if(dpi == DisplayMetrics.DENSITY_XXHIGH)
        {
            //xxhdpi
            folder = "drawable-xxhdpi/";

        }
        else if(dpi == DisplayMetrics.DENSITY_MEDIUM)
        {
            //mdpi
            folder = "drawable-mdpi/";

        }
        else if(dpi == DisplayMetrics.DENSITY_LOW)
        {
            //ldpi
            folder = "drawable-ldpi/";
        }

        return folder;
    }
public BitmapDrawable getDrawable(Context ctx, String imageName){
    String path = folder+imageName;
    ZipResourceFile zip;
    BitmapFactory.Options bfo = new BitmapFactory.Options();
    bfo.inPreferredConfig = Bitmap.Config.ARGB_8888;

    Bitmap b = null;
    try {
         zip = APKExpansionSupport.getAPKExpansionZipFile(ctx, 9, -1);
        InputStream is = zip.getInputStream(path);
         b = BitmapFactory.decodeStream(is, null, bfo);     }
    catch (IOException e) {
        e.printStackTrace();
    }
    return new BitmapDrawable(b);
}

所以，每当我需要一个图像时，我就像这样调用getDrawable：

newItem.setBackgroundDrawable(storage.getDrawable(this,"red_stored.png"));

但问题是，现在当我以编程方式执行时，图像看起来比我将它放入drawable-xhdpi文件夹并且android从该文件夹中自动选择它时要小。我该怎么做才能解决这个问题？