Overexposing V Underexposing

Started Feb 10, 2013 | Discussions thread
nixda
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Re: Expose to the Right vs DR Auto, DR200, DR400
In reply to Mark Weston, Feb 12, 2013

Mark Weston wrote:

With my X100, I shot DR100 and raw. I am waiting for my X100S to play with the Fuji parameters again, but this topic confuses me. It really seems like the Fuji DR settings are doing the opposite of expose to the right by underexposing and lifting the shadows instead of exposing to the right and bringing the highlights back. If I am understanding this correctly, I will likely stick with DR100 and use the histogram.

It is confusing. And it's not clear whether the camera is underexposing or overexposing until you look at the images later in a RAW converter.

Let's assume a given scene has a dynamic range of 10EV, from zero (black) to 10 (white). Let's also assume that the sensor is capable of capturing this scene without blowing any highlights. The JPG format can't accommodate the full amount of data, so the engine chooses what it thinks needs to be retained, guided by user-selected processing options.

Let's now say, the resulting JPG contains data in the range from zero (black) to 8EV (white). Thus the top 2EV are blown, i.e., anything that in the raw data falls into the 8-10EV range is now 8 and white.

Looking at the JPG, one would get the impression that one overexposed the shot, but in reality, the shot is 'overexposed' only with respect to the JPG conversion. The raw data do not contain any blown highlights.

Enter DR400. The camera now takes into account that the JPG conversion will likely blow highlights and adjusts the exposure such that that won't happen. In our example, the dynamic range of the scene is now no longer 0-10, but it is 0-8, which the JPG format can handle. If you now looked at the raw data, you'd conclude that the image was underexposed.

So, an image could be perfectly ETTR in its JPG version while at the same time being underexposed in its raw version. Likewise, an image can be perfectly ETTR in its raw version, but then, very likely, the ooc-JPG version will have blown highlights, and only some different tone mapping in post processing will preserve those, if desired.

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