Sigma SD1 / SD1 Merrill In-depth Review
Real world RAW advantages
Shooting RAW on the SD1 brings all the usual advantages - you can fine-tune processing individually for each shot, adjusting such things as white balance, brightness, and colour tone. It's therefore the format of choice if you're after the best possible image quality from your camera (and let's face it, there's little point in buying the SD1 if you're not). Perhaps the SD1's greatest strength in RAW is its exposure latitude, with RAW files containing considerably more highlight data than JPEGs.
Highlight recovery - studio scene
The SD1 behaves distinctly differently to most other cameras with regards to its ability to recover highlights from RAW that are blown in the camera's JPEGs. With conventional Bayer-sensor cameras we normally expect to see about a stop of luminance information in the highlights, but with ever-decreasing colour inaccuracy (as individual colour channels clip sequentially). The SD1 behaves somewhat-similarly at ISO 100, but switch to 200 or higher and it surpasses this dramatically, offering an extra stop of full-colour information in its RAW files that's simply not used in the JPEGs. This means that, at ISO200 and higher, the highlight range available in RAW at least matches the best APS-C DSLRs.
In the examples below we show how this looks using our standard studio scene. We've shot in JPEG+RAW firstly with correct exposure, then 1 and 2 stops overexposed. We've then pulled-back the RAW files to compensate, using the Exposure slider in Sigma Photo Pro. We're showing side-by-side crops from the Q60 colour checker chart in the upper right of the scene, comparing the overexposed JPEG and the recovered RAWs at ISO 100 and 200. Note that in the 'correctly-exposed' version of these shots, the lightest tones are approximately 1/2 stop from clipping in JPEG.
ISO 100, JPEG
ISO 100, RAW + SPP
ISO 200, RAW + SPP
|1 stop overexposed||+1 EV / -1 EV in SPP||+1 EV / -1 EV in SPP|
|2 stops overexposed||+2 EV / -2 EV in SPP||+2 EV / -2 EV in SPP|
In this example, at ISO 100 overexposure by a stop results in clipping of the lightest tones in the chart on the camera's JPEGs, but this data can be recovered accurately from the RAW file. However 2 stops overexposure and recovery is a complete no-go; some luminance information can be retrieved, but colour information is lost across much of the chart. In contrast, at ISO 200 and 2 stops overexposure, the results are essentially identical to overexposing ISO 100 by one stop. This means that you'll get maximum latitude for overexposure at ISO 200; we'd estimate you can expect to recover at least 1.3 stops above the JPEG clipping point with full colour accuracy. This in turn means that in bright, contrasty conditions we'd recommend using ISO 200 by default.
Real-world highlight recovery
Here we're showing a couple of examples of how the SD1's RAW highlight recovery can benefit your real-world shooting.
This is all very impressive stuff on the face of it, but it has to be kept in context. The SD1's huge RAW highlight recovery ability stems as much from the relatively-limited JPEG highlight range as anything else - the RAW files don't necessarily contain very much more highlight data than those from competing SLRs. We'd actually prefer to see that data used in the camera's JPEG processing, to give better highlight rendition (and therefore more usable images out-of-camera). This would also offer a more-accurate indication of what's in the RAW file when playing back your images.
RAW files for download
Here we provide RAW files, both from the review and the sample shots we take, to allow you to apply your own workflow techniques and see whether your experiences match ours.
- 1 Introduction
- 2 Specifications
- 3 Body and Design
- 4 Viewfinder
- 5 Operation & Controls
- 6 On-screen Controls & Displays
- 7 Menus
- 8 Using the SD1
- 9 Performance (Speed & AF)
- 10 Noise & Noise Reduction
- 11 Resolution
- 12 Dynamic Range
- 13 Raw Mode & Software
- 14 Raw Mode & Software
- 15 Medium & Low-res Raw
- 16 Image Quality Tests
- 17 Image Qual. Compared (JPEG)
- 18 Image Qual. Compared (Hi ISO)
- 19 Image Qual. Compared (Raw)
- 20 Conclusion
- 21 Samples