JPEG Tone curves / Dynamic range
Our Dynamic Range measurement system involves shooting a calibrated Stouffer Step Wedge (13 stops total range) which is backlit using a daylight balanced lamp (98 CRI). A single shot of this produces a gray scale wedge from the camera's clipped white point down to black (example below). Each step of the scale is equivalent to 1/3 EV (a third of a stop), we select one step as 'middle gray' (defined as 50% luminance) and measure outwards to define the dynamic range. Hence there are 'two sides' to our results, the amount of shadow range (below middle gray) and the amount of highlight range (above middle gray).
To most people highlight range is the first thing they think about when talking about dynamic range, that is the amount of highlight detail above middle gray the camera can capture before it clips to white. Shadow range is more complicated; in our test the line on the graph stops as soon as the luminance value drops below our defined 'black point' (about 2% luminance) or the signal-to-noise ratio drops below a predefined value (where shadow detail would be swamped by noise), whichever comes first.
Note: this page features our new interactive dynamic range comparison widget. The wedges below the graph are created by our measurement system from the values read from the step wedge, the red lines indicate approximate shadow and highlight range (the dotted line indicating middle gray).
Interestingly, the Coolpix A's tone curve is rather different to those employed by Nikon's DSLRs. The curve is an elongated 's' shape, giving a slightly lower-contrast response than the DSLRs but incorporating more tonal range in the highlights.
The Coolpix A uses a slightly different tone curve for each of its Picture Control presets. As you might expect, the Neutral and Portrait settings have slightly less contrast, while the Vivid setting has most. The camera allows you to tweak the behavior of each preset and displays each preset on a grid, showing their contrast and saturation in relation to one another.
The Coolpix A makes use of the Active D-Lighting system that Nikon has used in its DSLRs since the D300. Depending on the setting applied, this will reduce the exposure to increase the amount of highlight range captured. The camera then analyses the image and selectively brightens it, so that the final output represents the expected overall brightness, but with more tonal detail in the highlight regions, balanced shadow regions and a retention of local contrast.
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