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.
Preset Film setting
The Leica X1 has five 'Preset Film' modes, three color (Standard, Vivid and Natural) and two black and white (Natural and High Contrast), which can be modified in terms of contrast, sharpness, and saturation in five steps each. They use subtly different tone curves, which all offer about 3 stops of highlight range with fairly abrupt clipping to white. The main difference lies in the shadows; the 'B&W Natural Mode' gives relatively open shadows, whereas the 'Vivid' and 'B&W High Contrast' modes share a tone curve which blocks up the shadows quite quickly. 'Standard' and 'Natural' together occupy the middle ground.
The X1 offers five levels of contrast, and here we're showing the extremes based around the 'Standard' film preset. Increasing the contrast steepens the tone curve considerably, with harsh clipping to white, so this is best avoided if you wish to preserve highlights. Decreasing the contrast opens up the shadows even further than usual, to give results very similar to the 'B&W Natural' default curve, but gains nothing in the highlights.
ISO Sensitivity and Dynamic Range (JPEG)
The X1 maintains a very consistent JPEG tone curve throughout its ISO range. Low ISOs yield about 3 stops dynamic range in the highlights and 5 stops in the shadows, giving a total useable range of around 8.3 EV at lower ISOs (100 - 400). Increase the ISO to 800 and above, and the measured shadow range progressively reduces due to noise, suggesting a rather conservative approach to noise reduction by Leica (many manufacturers would simply smooth this away).
|Sensitivity||Shadow range||Highlight range||Usable range|
|ISO 100||-5.2 EV||3.1 EV||8.3 EV|
|ISO 200||-5.2 EV||3.0 EV||8.3 EV|
|ISO 400||-5.2 EV||3.0 EV||8.2 EV|
|ISO 800||-4.7 EV||2.9 EV||7.5 EV|
|ISO 1600||-4.3 EV||3.1 EV||7.4 EV|
|ISO 3200||-3.7 EV||2.9 EV||6.6 EV|
Dynamic Range compared
The X1 uses a rather conventional tone curve, which clips quite abruptly to white about three stops over middle gray. This means it gives very similar highlight range to the compact Micro Four Thirds twins, the Olympus E-P1 and Panasonic GF1. However it has relatively limited highlight dynamic range when compared to either the Sigma DP2 (the most similar camera, in terms of design concept, currently available) or the Nikon D300S (which uses a similar-sized 12Mp CMOS sensor), each of which offer about 2/3 stop more. This also places the X1 behind most modern DSLRs, which can offer up to 4 stops in the highlights (although in the case of Canon and Pentax cameras this comes via menu options, called 'Highlight Tone Priority' and 'D-Range' respectively).
In the shadows it's a different story, though, with the X1 using the most 'open' tone curve and dropping to black later than either the D300S or DP2. So X1 users could in principle get similar results to these cameras by underexposing by 2/3 stop, then pulling up the mid tones later. (Note the GF1's and E-P1's superficially better shadow range numbers almost certainly reflect noise reduction even at low ISOs).
|Camera (base ISO)||
|Leica X1||-5.2 EV||3.1 EV||8.3 EV|
|Nikon D300S (ISO 200)||-4.6 EV||3.8 EV||8.4 EV|
|Panasonic GF1||-5.4 EV||3.1 EV||8.5 EV|
|Olympus E-P1 (ISO 200)||-5.7 EV||3.4 EV||9.1 EV|
|Sigma DP2||-4.6 EV||3.8 EV||8.4 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. As with previous reviews we settled on Adobe Camera RAW for conversion to retrieve the maximum dynamic range from our test shots.
At the time of writing Adobe Camera Raw doesn't seem to understand the X1's DNG files properly and renders them rather too bright by default, applying a tone curve with a more gentle highlight roll-off but higher in mid-tone contrast which ends up rendering less overall dynamic range. Switching to ACR's 'Auto' setting pulls out another stop in the highlights compared to the JPEGs, although with no guarantee of color accuracy in the recovered areas; overall the file is rendered much too dark.
By playing with the sliders to give our 'ACR Best'*, we were able to extract a full 11.1 EV from an ISO 100 file, including one stop extra in the highlights over the JPEGs (with the same caveat concerning color accuracy), and extending well into the shadows. Needless to say an image converted with these settings would look pretty flat and dull, and would require further local adjustments to make aesthetically pleasing use of all that dynamic range, but this does give a good idea of the processing leeway available in the X1's raw files.
|ACR Default||7.5 EV|
|ACR Auto||9.3 EV|
|ACR Best||11.1 EV|
*'ACR Best' settings: Exposure = -1; Blacks = 0; Contrast = -50, Brightness = +100
WARNING: Although ACR is able to retrieve the 'luminance' (brightness) of wedge steps which were previously clipped there's no guarantee of color accuracy as individual channels clip before others.
To give an idea of what this means in practice, we shoot a high dynamic range scene using various levels of exposure, then attempt to pull back blown highlights in the raw conversion. This allows us to estimate roughly how much headroom there may be in the raw files.
In the example below, the 100% crop is taken from an area which is almost completely featureless and overexposed when following the camera's metering. Pulling the exposure down 1 EV in ACR recovers the lost detail in the brickwork almost (but not quite) perfectly, giving a result which is very close to that obtained by reducing the exposure one stop in camera.
|Metered (1/250 sec, F8, ISO 100)||100% crop|
|-1 EV compensation in ACR conversion||-1 EV exposure (1/500 sec, F8, ISO 100)|
If we then look at an image overexposed by stop in camera (so the brickwork completely clips to white), then pulled down by a stop in raw, again we see some highlight detail being recovered, but in this case rather less effectively, suggesting that the raw data itself has clipped, and ACR can no longer reconstruct image information in the highlights. Overall this suggests there's about a stop of extra highlight information recoverable from the raw files, but no more.
|+1 EV exposure (1/125 sec, F8, ISO 100)||+1 EV, -1 EV compensation in ACR|
Here are a couple more examples showing the kind of results you can get in normal use. The X1's metering is actually very protective of highlights much of the time, so you shouldn't have to do this often, but it's certainly a useful option to have available.
|Original JPEG||Original JPEG|
|100% crop, top right||100% crop, upper left|
|Raw + ACR, -1 compensation, 100% crop||Raw + ACR, -1 compensation, 100% crop|
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