Tag Archives: High Dynamic Range

Project Development

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Dynamic range

Human eyes have the fantastic ability of being able to handle a vast dynamic range -possibly well over 20 stops.  Thus a stained glass window can appear stunning to the naked eye with a range from almost clear glass to dark vibrant blue.  Sadly even the best cameras will only capture a small segment of this.

Dominic Price - Positions & Practice Oral Presentation

Each of the ten segments above is separated by 1/3rd of a stop.  It is clear that the white areas become washed out when overexposed by no more than 2 stops, but the blue areas require at least 3 stops more light in order to become visible.

Project Development

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Multiple Exposure Blending vs High Dynamic Range

Unlike the more consumer-oriented EOS bodies, the Canon EOS 1DX Mark II and its predecessors do not offer an in-camera High Dynamic Range (HDR) feature. As a result, the solution I worked towards in order to capture the high dynamic range found in stained glass windows was Multiple Exposure Blending (MEB).

Which ever process is used, a final image is created from a series of bracketed photographs (bracketing referring to taking a set of photographs in which one setting in the exposure triangle (ISO – Aperture – Shutter Speed) is changed. For each window I photograph, 20 images are captured each with a fixed ISO (50), fixed aperture (f/8.0) and varying shutter speeds (at 1/3rd stop increments).

It is possible to have HDR Software apply an algorithm to blend portions of the mages together through tonal mapping, but I much prefer the manual approach of MEB. By using layers in post production, I am able to select the optimum appearance of each glass element within the stained glass window and merge them together into one ‘optimum’ image. While this method is both time-consuming and skill-intensive, it achieves the most accurate results:

HDR - originalOne of twenty bracketed images, unedited.
HDR - EditedThe final image after Multiple Exposure Blending.

Increased Dynamic Range

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The promise of near-limitless highlight capture

The poor dynamic range found in normal cameras that so restricts the quality of stained glass window photography was the primary obstacle I had to overcome in my research.  However, a recent publication by German researchers from the Institut für Mikroelektronik Stuttgart (HERE) reveals a pixel design for massively increased dynamic range.

Existing CMOS chips ‘clip’ when they become saturated with light.  However, their ‘self-resetting pixel’ resets and has a circuit that counts how many times it has had to reset during the exposure.  It also contains a conventional analogue-to-digital conversion circuit, so it is also able to measure the remaining charge at the end of the exposure.

Such technology would mark an end to the need to limit exposure to protect highlight data.  Instead, optimal exposures for capturing the subject could be set, safe in the knowledge that this will not result in blown-out highlights.

CMOS.png

Realised CMOS tests chip: (a) the packaged chip, (b) the layout

Currently the work is focussed on video for industrial applications and is at a fairly early stage.  However, it should be transferable to still photography and would greatly improve the dynamic range of cameras, making it easier to photograph the interior of a church while maintaining the vibrant appearance of the stained glass windows.