Moonrise Over the Ocean and High Dynamic Range

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Images

Sometimes a single photograph cannot represent a scene the way it is remembered by the observer because the camera has less dynamic range than the human eye. One way to compensate for this difference is to combine multiple images to create a subjectively faithful reproduction of the scene as originally experienced. Below are two such composite images of the moon rising over Atlantic Ocean taken on successive Cape Cod evenings. Note the dramatic affect that different atmospheric conditions can have on the color and mood of the pictures.

 


Discussion

High Dynamic Range

The first four images below were created with different shutter speeds to try to capture one that had the proper overall exposure for the entire scene, but even in the best case the moon is drastically overexposed to the point that it contains no discernible features such as were visible during the live viewing. This is a case in which the overall brightness range of the scene was so great that the camera was incapable of recording detail in the darkest shadows and brightest highlights in a single exposure.  In other words, the dynamic range of the camera was exceeded by the brightness range of the natural scene. To compensate for this a series of images of the moon were made at much higher shutter speeds in order to capture one that appeared natural, and then in Photoshop that one was used to replace the blown-out moon in the picture that was selected for best overall scene exposure.

The “manual” method described here for achieving a high dynamic range image can be done automatically in many modern cameras, including mobile phones, that have an HDR option.

All of the images below were exposed with a Nikon D800 camera and 200mm lens at ISO 400 and f/4.0.

White Moon Image

This picture was created from two images in the same manner that the orange moon picture was, but in this case the moon appeared much brighter in the live scene and did not have as much discernible detail in it. It was processed accordingly using the same image of the moon as in the other picture. The full scene was exposed with the D800 at ISO 1000, 8/10 sec., f/8, and with a 24-70mm zoom lens at 70 mm.

Human Vision

The human visual system combines the optical performance of the eye with neural signal processing to perceive a dynamic range of up to 20 stops compared to about 12 stops for the the camera at ISO 400. This means that the observer will originally witness and remember a scene with visible details in the dark shadows as well as details on the surface of the moon itself, while no single exposure by the camera will be able to produce a comparable image. In the orange moon scene the exposure for the separate image of the moon is about 6 stops lower than the image of the full scene, resulting in an overall scene brightness range of roughly 18 stops.

 


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