Luminance masking..it is a method to process your photo so that the final output is a well balanced exposure..the noise is keep as low as possible and no blown out highlight.  It is a method that combine multiple of same photo but under different exposure.  Usually, we combine 3 photos and 5 photos, it is depends on what output you want to achieve.

Previously, this method was too tricky and too hard to be done. The person need to have skills in photoshop, but thanks to Jimmy McCantier who developed a plug-in Luminance masking for photoshop,