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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 cameras) black to clipped white (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' 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 the camera can capture before it clips to white. Shadow range is more complicated; in our test we stop measuring values below middle gray 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.

Custom Image Modes

The Bright, Natural, Portrait, Landscape, Vibrant, and BW use essentially the same curve and therefore produce the same amount of dynamic range. The Muted setting uses a more linear, less contrasty curve but all the settings clip highlights at the same point.

Contrast

The K-7 features contrast settings (as a part of the custom image parameters) from -4 to +4. As you would expect the -4 setting produces a flatter tone curve while the +4 setting results in a more extreme s-curve. Most of the custom image settings use a contrast setting of either 0 or +1, while the Muted setting uses -3 to generate a small extra amount of shadow dynamic range.

Expanded Dynamic Range Function

The K-7 features both shadow and highlight expansion which can be applied to the camera's JPEG output. With Highlight correction activated ISO 200 becomes the minimum sensitivity setting. With highlight expansion turned on the tone curve is flatter in the highlights and produces an extra stop of highlight range.

With our dynamic range test setup we could not trigger the shadow expansion functionality and therefore we can unfortunately not provide any measurements for this feature.

ISO Sensitivity and Dynamic Range

While the K-7's highlight range remains relatively constant the measured shadow range decreases as you go up the sensitivity scale. This is mainly due to increased noise and noise reduction smearing.

Sensitivity Shadow range Highlight range Usable range
ISO 100 -5.7 EV 2.9 EV 8.6 EV
ISO 200 -5.5 EV 2.9 EV 8.4 EV
ISO 400 -5.5 EV 2.9 EV 8.4 EV
ISO 800 -4.3 EV 2.9 EV 7.2 EV
ISO 1600 -3.4 EV 2.8 EV 6.2 EV
ISO 3200 -2.1 EV 2.7 EV 4.8 EV
ISO 6400 -1.3 EV 2.4 EV 3.7 EV

Dynamic Range compared

At it default settings the K-7 produces slightly less dynamic range than its predecessor and the Nikon D300. It squeezes past the EOS 50D in terms of overall range but still comes last in this comparison in terms of highlight dynamic range.

Camera (base ISO)
Shadow range
Highlight range
Usable range
Pentax K7 -5.7 EV 2.9 EV 8.6 EV
Pentax K20D -5.8 EV 3.2 EV 9.1 EV
Nikon D300 -4.7 EV 4.1 EV 8.8 EV
Canon EOS 50D -4.8 EV 3.5 EV 8.3 EV

The wedges below 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).






RAW headroom

There is usually slightly more dynamic range to be obtained from RAW capture compared to in camera JPEGs (thanks to the use of a consumer-friendly tone curve in the JPEG conversion). This is typically around 1 or 1.5 EV (one to one and half stops) or so of extra information available at the highlight end in RAW files and that a negative digital exposure compensation when converting such files can recover detail lost to over-exposure. As with previous reviews we settled on Adobe Camera RAW for conversion to retrieve the maximum dynamic range from our test shots.

Adobe Camera RAW's default is fairly contrasty and, as expected, produces less dynamic range than the out-of-camera JPEG. The best result we could achieve in ACR by applying some negative digital exposure compensation, reducing contrast and increasing brightness is 10.5 EV of which just over one stop (1.2 EV) is additional highlight range.

  • ACR Default: Exp. 0.0 EV, Blacks 5, Contrast +25, Brightness 50, Curve Medium
  • ACR Best: Exposure -1.05 EV, Brightness 100, Contrast -50, Curve Linear
Settings Usable range
JPEG 7.8 EV
ACR Default 7.0 EV
ACR 'Best' 10.5 EV

These measurements are more or less in line with what we found in real world use. Parts of the image which are more than 1 stop over exposed are usually not recoverable at all or produce false color information when negative digital exposure compensation is applied in a RAW converter.

In the first example an area of the image (the bench) is over exposed by more than one stop. Reducing the exposure by three stops in Adobe ACR recovered only a small amount of detail and some of that recovered detail turned gray. The second sample shot is less extreme and some, but not all, detail is recovered by applying one stop of negative digital exposure compensation.

Adobe Camera RAW default conversion Adobe Camera RAW with -3.0 EV digital comp.
Adobe Camera RAW default conversion Adobe Camera RAW with -1.0 EV digital comp.
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