AutoDesk Smoke :: Resize - Simple Way To Scale Proportionally?

i have an image H:3639 W:4849 , now i want to resize it proportionally down to smaller resolution. Why there's no fast way to do scaling proportionally for example 2x , 3x or 1/4x etc. In above example , the only way is by using calculator and input a new custom destination resolution. My opinion is : there should be a button to grab whatever the source size and paste it into the destination h/w and then need a feature to lock the ratio , so while i change the w , the h will adjust automatically (simply like the 'prop' mode in the source area) . Right now i have to do too many 'click' and 'click' just for that simple task.