Exposure control in a raw developer: misnomer?

Started Jan 30, 2013 | Discussions thread
AlbertInFrance
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Re: Exposure control in a raw developer: misnomer?
In reply to dosdan, Jan 30, 2013

For me, the exposure at the image plane is defined by the subject reflectivity, the incident illumination, the aperture and the shutter speed. The image exposure is further affected by the photosensitivity of the sensor (ccd, film ...).

With a camera where you can physically change the sensitivity of the sensor (increasing the gain or pushing film development) then the image exposure is affected by that change. There may be other effects (noise, grain, contrast ...) but the image density (for film) or the recorded numerical values (digital) for a given image plane exposure will be modified. This will allow you to modify the image plane exposure.

If you have a camera where the photosensitivity of the sensor is fixed then any post-processing changes merely select different ranges of values from those that were recorded when the photo was taken. Thinking of a classic H&D curve you can use different parts of the curve (print only the highlight end or just the shadow end). Eventually you will move into the shoulder or the toe and lose tonal range.

Similarly, if you got the image exposure 'wrong' (non-optimal) you can make adjustments in post processing, but ultimately you are restricted by the range of tones that were recorded by the camera. For a digital system the amount of leeway you have depends on the relative H&D curves of the RAW file and the JPEG, print or whatever that is used for display.

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Albert
Every photograph is an abstraction from reality.

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