Images and videos can be touching, triggering emotional responses or even changing the mood of the observer. The response is influenced both by the image content as well as the appearance of the image. In this paper, we investigate how solely simple image processing, i.e., modifying the brightness, the saturation, or the color temperature, actually changes the emotional perception. We collect empirical data on images associated with emotion labels and analyze the valence ratings of the different modifications and their strengths. We show that these relationships tend to be linear only in a limited range while sometimes stronger modifications lead to the opposite effect. Pushing the modifiers towards the boundaries we derive from those ranges and combining them successfully shifted the emotional affect on 92% on around 80 samples. From these findings we derive our EmoTune filter which allows for almost linear control by combining specific modes and demonstrate successful application to both images and videos.