1 pixel at what resolution? Double your resolution, and that one pixel will be half the previous size, quadruple it and it will be one fourth. If I get a photo and have to remove, say, the background around a vehicle, I have to draw a mask. Since most digital photos from cameras are 72 ppi, I increase it to 300, so that I have more control. So, increase your resolution; it won't change the way your image looks, but you'll be able to cut a finer trap.
Steve