Elasticity of exposure

I felt like adding this very brief page just to make a point that many will not believe.

Here again is a screen capture from Photoshop CS6 of the Zone 0 exposure I used in my previous explanation of the Zones.

Zone 0, untouched

Zone 0, untouched

In the last page, I made a claim that Zone 0 carried far more information than people gave it credit for. You wouldn’t look at this and believe that there was much hidden detail or texture would you. But, here is the same NEF brought through Adobe Camera Raw with a 5-stop exposure enhancement.

Zone 0 exposure + 5 stops

Zone 0 exposure + 5 stops

Lo and behold, a touch more noisy than the Zone V exposure, but not bad at all. The mean L-Value is a proper 54 and the standard deviation is over the central part of the image is 18, which includes the elevated noise.

For grins, here is the Zone I exposure with 4 stops of exposure added in ACR:

Zone I exposure + 4 stops

Zone I exposure + 4 stops

The average value comes in nicely at 52 and the standard deviation is 14.66, closer to the 13 or so of the Zone V exposure, indicating a good deal less noise, which is visually apparent. Here is a nice JPG buried in Zone I.

This does not work the other way around; that is, we cannot recover information from the highest exposure in the same manner. Here is the Zone X exposure brought down in ACR by 5 stops:

Zone X exposure -5 stops

Zone X exposure -5 stops

It is apparent that the textures have been washed out, even though the mean value is about right at L=50. This is reflected in the histogram which shows a standard deviation of only 3. You should note that I am showing the full sized image capture in this screen shot: the small amount of texture left in the lower right is due to vignetting in the full capture.

Here is the Zone IX exposure knocked down in ACR by 4 stops:

Zone IX exposure -4 stops

Zone IX exposure -4 stops

The average value is a touch high, at 60 instead of 54 or so. However, there is little noise and the standard deviation is just about right at 13. Note that even though this range was significantly compressed down when the exposure was left untouched, it has expanded back as we reduced the exposure in ACR from Zone IX to Zone V.

In short, there is a great deal of elasticity in a digital capture at base ISO.

Once more, to emphasize: don’t be afraid of the dark: there’s an entire JPG capture lurking in there.

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