Sigma DP1 Review
Our new 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.
Below you see the tone curves for the minimum, maximum and default contrast settings. None of the settings provides more shadow range than the others, all curves clip the shadows at pretty much the same point. The high contrast setting will cost you about half a stop of highlight detail though.
ISO Sensitivity and Dynamic Range
The DP1 produces fairly consistent dynamic range across all sensitivities. It starts at 8.8 stops at base ISO and drops very slightly to 8.5 stops at ISO 400. At ISO 800 the Dynamic range measures actually at 8.9 stops but this is due to the very marginally flatter curve in the shadows and won't give you any visibly higher DR. These figures are actually quite impressive. In the Dynamic Range area the DP1 is unmatched by any other compact cameras and even leaves some entry level DSLRs behind it.
|Sensitivity||Shadow range||Highlight range||Usable range|
|ISO 100||-5.0 EV||3.8 EV||8.8 EV|
|ISO 200||-4.9 EV||3.8 EV||8.7 EV|
|ISO 400||-4.7 EV||3.8 EV||8.5 EV|
|ISO 800||-5.1 EV||3.8 EV||8.9 EV|
Dynamic Range compared
As you can see the DP1 produces half a stop more highlight range than the D60 and almost an entire stop more than the D40. It also offers softer 'roll off' at the highlight end which will deliver less hard-clipped looking white highlights. On the down-side it cannot keep up with the D60 at the shadow end where the Nikon has approximately a 2/3rds of a stop advantage. DP1 and D40 are on par in the shadow area and clip roughly at the same point.
|Camera (ISO 100)||
|Sigma DP1||-5.0 EV||3.8 EV||8.8 EV|
|Nikon D60||-5.7 EV||3.3 EV||9.0 EV|
|Nikon D40||-4.9 EV||2.9 EV||7.8 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).
Experience has told us that there is typically around 1 EV (one stop) 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. For the purpose of this comparison we converted the DP1's RAW files at Photo Pro's default setting and with a set of parameters that would give us a maximum dynamic range.
Applying Photo Pro's default settings to a RAW file will give you approximately 1 1/3 stops more shadow range compared to an out-of-camera JPEG (though you'll see more noise). Using Photo Pro Parameters in order to maximize dynamic range will increase the shadow range by 1 2/3 stops and the highlight range by one stop, though in truth (as the example below shows) this is more about SPP's rather excessive processing (contrast masking) than the sensor's abilities; you won't see much detail appearing in clipped areas, just a gradual flattening of the image, and the introduction of false color.
- SPP Default: Contrast 0, Shadow 0, Highlight 0
- SPP Best: Contrast -1.6, Shadow +0.2, Highlight +1.1
|JPEG||-5.0 EV||3.8 EV||8.8 EV|
|SPP Default||-6.4 EV||3.9 EV||10.3 EV|
|SPP Best||-6.7 EV||4.8 EV||11.5 EV|
WARNING: Although Sigma Photo Pro was able to retrieve some 'luminance' (brightness) of wedge steps which were previously clipped there's no guarantee of color accuracy as individual channels may clip before others. This can be seen in the examples below.
The negative digital exposure compensation has revealed some more detail but the blown out sky has a slightly pink tint and there's not a lot of 'real' information being revealed. In fact all that's really happening here is that SPP is gradually flattening the image out, and compared to most SLRs we test there really isn't a lot of room for recovering highlight detail in washed out areas.
|Sigma Photo Pro default conversion||Sigma Photo Pro with -2.0 EV and Highlights -2.0 comp.|
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