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).
As expected, the SLT-A99 has a tone curve that is virtually identical to previous Sony Alpha models. Absent any DRO enhancements, this yields almost nine stops of dynamic range, placing it comfortably among its full frame peers. The roll-off from clipped whites to highlight detail on the A99 is just a touch steeper than we see from the Canon EOS 5D Mark III.
The effect of Sony's 'DRO+' settings differs depending on the scene, so this test, performed using our 18 step wedge, isn't necessarily an accurate indication of 'typical' performance with a real-world subject. It does clearly show, however, the way in which DRO+ is designed to work, extending incrementally the amount of mid tones by lifting the shadow areas, to get the most detail out of these areas from a single exposure.
The A99 offers no fewer than 13 different 'Creative Styles', which are essentially color response presets applied to in-camera JPEGs. Each style can be adjusted for contrast, sharpness and saturation. The Deep and Light presets darken and brighten the image by about 1/3 stop EV, respectively. The Vivid, Landscape, Sunset and Black and White presets all boost contrast, primarily by way of heavier shadow tones.
As is the case with Nikon and Canon DSLRs, the A99's ISO 50 mode is an 'extension' ISO sensitivity setting, which gives roughly 0.7 EV less highlight dynamic range than ISO settings of 100 and higher. The likelihood of highlight clipping then, should serve as a caution against enabling ISO 50 when shooting in very bright situations - precisely the conditions that are at great risk for blown highlights.