High Dynamic Range Image Fusion Using M42

Many brighter deep-sky objects contain regions that include faint details, and high dynamic range (HDR) image processing techniques help the astrophotographer portray the essence of those objects in a single display. The Great Orion Nebula (M42) is a prime example with the stellar nursery near the Trapezium greatly outshining the surrounding tenuous nebulosity. Exposing a single frame for the faint outer regions saturates the bright Trapezium region whereas a properly exposed Trapezium photo fails to capture the faint regions. Using different exposures optimized for the separate sections of the target, the HDR method re-sculpts the brightness contours to squeeze the extremes into a single image. Of course, the result is photometrically incorrect, as relative brightness levels have been heavily modified creating plateaus and even reversals in the profiles where none previously existed. However, the Trapezium stars and the faintest filaments come together in a pleasing if slightly surreal display using limited display depth inherent in even the best monitors.

Separate Images

20 x 1.6 sec16 x 6 sec16 x 25 sec14 x 100 sec

Each of these images is a combination (stack) of multiple images taken at a given exposure setting as indicated above to improve the signal-to-noise. AstroArt is the tool used, although there are a myriad of tools available to perform this task. These four images were then imported into Photomatix Essentials to produce the fused HDR image below.