Do you create the MDPI drawable first and just scale it accordinly to the .075/1.00/1.50/2 ratio by pixels in photoshop or do you recreate each individual drawable?
Looks like there's a tool in Android Studio:
Expand your project folder in the Project View > right click on app > New > Image Asset
Icon Type: Action Bar and Tab Icons
Asset Type: Image
Choose the Path for original image (it should be big)
Shape: None (to make background transparent)
And it will generate the images in the appropriate drawable folders.