I am trying to vectorize the contours (skewed rectangle) of the TV in the following original image.My first step is applying threshold. Tried selection of threshold values based on what skimage has to offer, but non of them managed (for example) to separate correctly the little fawn to the left, or the TV stand from the TV border. For example this is the result using yen's method:Can you suggest any preprocessing that may help before applying a threshold ?  
Suggested image preprocessing before applying threshold
transformations;color;filtering