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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. You can compare the dynamic range of images captured using the camera's various parameters, or you can select up to three other cameras to compare. 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).


The SD1's JPEG tone curve offers about 3.3 stops of highlight range above metered middle-grey, which is a slightly pedestrian performance compared to its peers. Both the Nikon D7000 and the Sony SLT-A77, for example, offer substantially greater highlight range. The SD1 is closer to the Canon EOS 7D's default behaviour, but lacks any kind of highlight-expansion mode analogous to Canon's Highlight Tone Priority. In the shadows, all of the cameras use very similar tone curves.

The upshot of this is that when shooting JPEG with the SD1 in contrasty conditions, you have a choice of either allowing highlights to clip, or underexposing to protect them. If you shoot Raw, it's important to appreciate that all of the feedback the camera offers about exposure in playback mode - i.e. the highlight clipping warning and the image histogram - is based on the camera's JPEG processing, as its generated from the preview image that's embedded in the Raw file. We'll look at the practical implications of this later in the review.

Color Modes


Here we're showing that all of the SD1's Color Modes are based on essentially the same tone curve, and therefore the JPEGs clip at the same point in the highlights. Instead the modes differ based mainly on saturation and colour tone, with Landscape being warm and saturated, for example.

JPEG contrast settings compared to SPP-converted RAW


This graph compares the SD1's range of JPEG contrast settings with a Raw file converted through Sigma Photo Pro at default settings (i.e. Standard Color Mode, Contrast =0). There are some notable points here that have a real operational impact for both JPEG and Raw shooters:

  • The in-camera Contrast setting doesn't just change the steepness of the tone curve, it also changes the highlight clipping point. This is mostly a problem if you increase the contrast setting; highlights will clip earlier.
  • Setting contrast to -1 clips at about the same point as the default setting (or perhaps a tad higher), but does so quite abruptly, with no roll-off.
  • Raw files converted using Sigma Photo Pro use a different tone curve that resembles the default contrast setting in the highlights, but the +1 setting in the shadows.

One less-obvious, but useful point to come out of this relates to the highlight clipping warning in playback, which is triggered at a distinctly conservative value of 248. If you shoot Raw, then setting contrast to -1 will make this warning more-closely reflect where highlight data actually clips at ISO 100.

However, it's also worth bearing in mind that, because the SD1 retains a stop more highlight data in its Raw files at all higher ISOs that's simply not represented in its JPEG output, the clipping warning doesn't really mean anything useful for Raw shooters at these ISOs.

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Comments

Total comments: 3
Birtrum

I purchased an SD1 for my business of photographing textiles in a studio situation and I feel totally deflated. The actual image quality is excellent, but the tethering capabilities are pathetic. I expected to be able to click from my PC to launch a shot, then instantly see what I had taken, before moving on to the next item, which sadly is not the case. Their software application known as Sigma Capture Pro should be reported to the trading standards council, as there is nothing 'Pro' about it as it is just a glorified remote shutter release program. Furthermore in order to have access to your images on a PC, you need to go into the menu function on the camera and disable the 'remote capture program' then select mass storage to view your images. Going through this process with every shot, may be good for you cardiovascular system, but for someone who relies on seamless throughput to make a living, this camera is junk.

1 upvote
Scottelly

I was looking at the photo comparison today, comparing the SD1 against the new Canon 5 D Mk III, the Nikon D800E, and the Pentax 645 D . . . at ISO 800 . . . and I just can not believe my eyes. Take a look at this:

http://sbkart.com/sd1/SD1-screencap.jpg

The SD1 never ceases to amaze me.

2 upvotes
Scott Greiff

Why won't the comparisons load?

0 upvotes
Total comments: 3