public void extractMaxImage(string archiveDir = null, string fileName = null)
{
// select max image size, excluding void images with offset = -1
ImageSize maxImgSize = imgList.Where(img => img.offset != -1).Max(image => image.imgSize);
// extracting max image
extractImage(imgList.Find(img => img.imgSize == maxImgSize), archiveDir, fileName);
}