I don't quite understand what you are asking.. but try this. Take the original image dimensions, and multiply both the width and height by the % zoom that you like. Then resize your original image to those dimensions. For example: if the original image is 1920x1080, but you like the way it looks at 66% zoom, then multiply 1920 and 1080 by 0.66 to get 1267 and 713 respectively. Then resize the image to 1267x713. Then save the image. Let me know if that works for you.