How to decrease image size twice in conversions

[firdavsibodullaev]

If I write some exact size in conversions, it is easy

, but I want to decrease image size twice depending on image's own size. I used this method

Then I found 1 issue, during retrieving conversions, code reads this method and it takes too much time to retrieve, I could not find any way to get file's own width and height. There is no ability to access these data

How can I realize this logic adequately?