Previous page Next page

Dynamic Range

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.

Dynamic Range Optimization feature

One feature we first saw introduced with the DSLR-A100 is 'Dynamic Range Optimization', designed to deliver lighter shadow areas by boosting the lower end of the tone curve. The A100 provided just three options (Off, Standard and Advanced), the A700 expands this to Off, Standard, Advanced Auto and then five manual levels (Lv1 - Lv5). The A100 also imposed limits on when you could use DRO (certain metering modes, not RAW etc.), the A700 has no such limitations.

As you can see from the graph below (using our standard step wedges test shot) the A700 actually achieves this brighter shadow response by modifying the tone curve, each of its five levels enhancing this shadow boost (we were only able to plot the first three levels as the last two lifted our reference black levels too high for measurement to be made accurately). As you can also see from these plots the Standard and Advanced Auto settings produced slightly lighter midtones but didn't affect shadow response. Note that the big advantage to doing this kind of tonal manipulation in-camera is that it is applied to RAW data before it becomes a JPEG.

Dynamic Range Optimization studio samples

Sony's DRO system appears to be able to work at either end of the tonal range (lifting / maintaining highlights as well as boosting shadows). The most likely scenario for use however is to boost dark shadow areas of the image. We designed simple studio test scene to test DRO's ability to lift shadow detail. Half of the scene is directly lit, the other half in direct shadow. Looking at the first shot in the sequence below (DRO Off) you can see how the histogram looks in this scenario, a large gap in the center.

Take a little time to look down this sequence and you'll see that Sony's DRO options really do work (for this kind of scene). What didn't work in this scenario were the 'Standard' and 'Advanced Auto' options.

  Thumbnail Luminosity histogram
O
f
f

S
t
d

A
d
v

A
u
t
o

A
d
v

1

A
d
v

2

A
d
v

3

A
d
v

4

A
d
v

5

When DRO Standard works

The two images below have identical exposures (1/100 sec, F8 @ ISO 200) however the second image which has the DRO 'Standard' setting is clearly lighter, in this scenario DRO is apparently looking at the histogram and deciding that the image is slightly underexposed and adjusting the tone curve accordingly.

  Thumbnail Luminosity histogram
O
f
f

S
t
d

DRO Advanced Level 5 comparison across the ISO range

Of course one disadvantage to lifting the shadows is that you are also amplifying noise by the same amount, and because so few bits 'describe' the dark areas of the image this means that at its highest setting the DRO level will inevitably lead to increased noise in those lifted areas. As you can see from the crops below noise levels in these lifted areas becomes pretty much unacceptable from ISO 800 upwards.

  Thumbnail 100% crop
1
0
0
2
0
0
4
0
0
8
0
0
1
6
0
0
3
2
0
0
6
4
0
0

Dynamic Range Optimization real world samples

As you can see from the samples below (this mirrored our experience using this feature numerous times in the field) the 'Advanced Auto' mode seldom made any difference to shadow brightness, instead we would recommend using the manual ('Advanced') DRO option which can be surprisingly successful for scenes like this with huge differences in brightness.

DRO Off DRO Advanced Auto
 
DRO Advanced Lv5  
   
DRO Off DRO Advanced Auto
 
DRO Advanced Lv5  
Previous page Next page

Comments