Super Dynamic Range

2019-12-05 • SEND FEEDBACK •
Related: dynamic range, Expose To The Right, exposure, noise

This article is part of a series. See Introduction to Camera Features to start.

Here, dynamic range is focused primarily on ultra-clean shadows that are noise-free or nearly so, all while avoiding any blown-out highlights. It is laughable to read of cameras with “14 bit dynamic range” when the lower order bits are so overlaid with random gunk—real dynamic range into shadows means signal fidelity (S/N ratio) as clean as in mid-tones at least.

To obtain ultra low noise shadows, more exposure is needed:

• Take more frames and average them (frame averaging),
• Increase the exposure time for the frame as a whole, thus blowing out highlights but hugely improving dark areas.
• Hardware advances. For example, capturing overflow bits on an individual photosite basis. For example, adding a 4-bit overflow counter to each photosite would yield 16X the dynamic range (4 stops). Allowing 4 more stops in dark areas would cut noise by a factor of four.

Of the above, frame averaging is readily achievable, but has issues like subject movement and is relatively inefficient at addressing the core problem of too little exposure in very areas, requiring very large numbers of frames to average out what is mostly noise, and often contaminated with large numbers of hot pixels.

Proposal (with current hardware capabilities)

Modern digital cameras with electronic shutters can use the classic technique of bracketing, the idea being seamless and automatic “invisible bracketing”. The actual implementation could vary but the basic idea is that the camera invisibly takes several exposures according to the scene.

For example, the camera would take an ETTR exposure, followed by one or more brighter/longer exposures. The camera would seamlessly improve the darker areas by using the brighter exposure data, using appropriate smarts to prevent edge brightness oddities.

Requirements:

A tripod is presumed, but might not be necessary with sensor advances and in bright conditions.

• Interacts and can be used with Optimal Exposure / ETTR and Super Dynamic Range.
• Lossless-compressed raw file for all frames.
• Option to retain the first/single/ETTR exposure in addition to the merged SDR exposure.
• Premised on the user of auto-ETTR mode.
• Smart detection of motion, rejecting or averaging problem areas.