I usually have a screen size of 1280x720 for landscape and 540x960 for portrait, then in photoshop I'll set my layout to match and transform my images to the size on screen which I like, I use vector images so I paste those in and scale down, don't loose much quality then. Export to png and add in as a sprite. Hope this helps. This way I don't need to scale or resize my images in construct 2.