Every time you press the shutter on the Pixel 2, the camera takes up to 10 photos. If you’re familiar with typical HDR, you’d expect each photo to have a different exposure in order to optimize detail in the highlights and shadows. HDR+, however, takes images at the same exposure, allowing only for naturally-occurring variations like noise, splits them up into a grid, then compares and combines the images back into a single photo. Individually, the images would look dark to prevent highlights from blowing out, but the tones in the shadows are amplified to bring out detail. A machine learning algorithm recognizes and eliminates digital noise, which typically happens when you raise exposure in dark areas.