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Pentax K-r Dynamic Range (JPEG)

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).

Highlight Correction

The K-r features Pentax's shadow and highlight protection which is applied to the camera's JPEG output and the results are virtually identical to what we've previously seen on the Pentax K-x. With Highlight correction activated ISO 200 becomes the minimum sensitivity setting. The tone curve is also flatter in the highlights and produces approximately one extra stop of highlight range. As with previous Pentax DSLRs our dynamic range test setup was not able to trigger the shadow expansion functionality and therefore we can unfortunately not provide any measurements for this feature.

The sample shots of our studio scene below show the K-r's highlight protection at work. The original shot has been overexposed by approximately 1.5EV which leads to a loss of highlight detail in various areas of the image. If we apply 1EV negative digital exposure compensation to the RAW file some, but not all detail can be recovered. There is also some evidence of channel clipping, resulting in a loss of color information. The camera's highlight protection system can recover at least a small amount of highlight detail, it's therefore worth leaving it on when shooting high contrast scenes.

Out-of-camera JPEG - Highlight protection off
ACR conversion - 1EV negative digital exposure compensation
Out-of-camera JPEG - Highlight protection on

The real-life samples below that the K-r has a relatively small 'RAW headroom'. The camera has a slight tendency to overexpose high contrast scenes which in this case has lead to some burned out areas in the sky. Applying negative digital exposure compensation in RAW conversion brings a small amount of detail back but, as one or more color channels have clipped, color information has been lost. When shooting scenes like this we would recommend to always some negative exposure compensation.

Out-of-camera JPEG - Highlight protection on
ACR conversion - default settings
ACR conversion - 1EV negative digital exposure compensation

Like previous Pentax DSLRs the K-r lets you choose from a range of image modes. The Bright (default) , Natural, Portrait, Landscape, Vibrant, and Monochrome image modes use essentially the same curve and therefore produce the same amount of dynamic range. The Muted setting uses a more linear, less contrasty curve and Bleach Bypass and Reversal Film have higher contrast but all settings clip highlights at the same point.

The K-r's highlight range remains relatively constant across the sensitivity range. However, as one would expect the measured shadow range decreases as you increase sensitivity. This is mainly due to increased noise and noise reduction smearing.

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