Reduced-resolution Raw

Unusually, the SD1 can record Raw files in three different resolutions, which Sigma calls High, Medium and Low. Changing the Image Size setting affects both Raw and JPEG - so you can't record a full-size Raw alongside a small JPEG for indexing purposes, for example. Medium-sized files are 3264 x 2176 pixels (~7MP), while the Small setting offers 2336 x 1568 px (3.7MP). File sizes are variable, but roughly proportional to the pixel count; so for a scene that would give a full-size Raw of 50 MB, Medium would give 25 MB and Low 12 MB.

The big question is whether it's worth shooting at these reduced sizes. We've addressed this using three tests; resolution (using our standard resolution chart), sharpness and detail (using our studio test scene) and high ISO noise (using our occasional low-light test scene).


Here we're showing our standard resolution test chart at Medium and Low resolution, looking at Raws processed using Sigma Photo Pro. The corresponding out-of-camera JPEGs are also available for comparison.

Medium (3264 x 2176), Camera JPEG Low (2336 x 1568), Camera JPEG
Medium (3264 x 2176), Raw + SPP Low (2336 x 1568), Raw + SPP
Medium, SPP-converted Raw, 100% crops Low, SPP-converted Raw, 100% crops

In Small, the camera gives very clean output in both JPEG and Raw. In contrast, when shooting at Medium resolution the camera's JPEG output looks markedly cleaner than its Raws, which show odd artefacts on diagonals. The crops below show that these 'jaggies' are strongly dependent upon the angle of the lines, and those with a shallow gradient are worst-affected. Jaggies on resolution charts are in no way the sole arbiter of image quality, but this isn't very good.

Medium Raw + SPP, 100% crops

Sharpness and Detail

Medium (3264 x 2176), Camera JPEG Low (2336 x 1568), Camera JPEG
Medium (3264 x 2176), Raw + SPP Low (2336 x 1568), Raw + SPP
Medium, SPP-converted Raw, 100% crops Low, SPP-converted Raw, 100% crops

There's really no getting away from the fact that, while Small is providing crisp, detailed output, Medium looks disappointingly soft, and isn't as good as we'd hope given the level of detail the SD1 can resolve at full resolution. To show this more clearly, here's a side-by-side comparison of a couple more 100% crops against a High resolution image downsampled in Photoshop (using the default Bicubic algorithm), which shows finer detail and fewer artefacts (e.g. jaggies). To an extent this can be rectified simply by sharpening the converted Medium Raws in Photoshop, of course, but that will also have the affect of accentuating any artefacts in the Medium file.

Medium, SPP-converted Raw, 100% crop Downsampled full-resolution Raw, 100% crop

Low light High ISO

Here we're looking to see whether using lower resolution offers improved results when using high ISOs in low light. This scene was lit by halogen light, with a colour temperature of about 3000K. We're comparing the reduced-size Raw files converted using Sigma Photo Pro with a full resolution Raw converted then downsampled to the same size. The crops shown are also downsampled (50% rather than 100%).

Low-light comparison: 1/6 sec F8 ISO 3200; colour temperature ~3000K
Medium High, downsampled
50% crop 50% crop
Low High, downsampled
50% crop 50% crop

The SD1's biggest problem at high ISO is low-frequency green and purple colour blotching in shadow areas, which renders many images unusable and is difficult to treat effectively in post-processing. Interestingly, shooting reduced resolution Raw appears to reduce its intensity in these comparisons. Sadly, though, it's in no way a cure; the effect is still very much there, and none of these files would make an acceptable print.

Neither does reducing the resolution do anything to help the severe drop in colour saturation that plagues the SD1's files at high ISO. Of course it's possible to combat this by changing the colour mode to one that's more vibrant, or increasing saturation in post-processing, but this just accentuates the chroma blotching even more.

Overall Verdict

These three tests aim to give some kind of indication of the effects of shooting reduced-resolution Raw on image quality. We find Medium resolution to give unexpectedly soft results and to be subject to some odd artefacting, most obviously 'jaggies' on shallow-gradient diagonal lines. Low resolution, however, gives much cleaner images - but at less than 4 MP, they're only really going to be suitable for web use or small prints.

Using smaller image sizes does have some operational advantages - you get faster continuous shooting, and shorter write times which makes the camera less-objectionable to use. So in certain circumstances it may well make perfect sense. Overall, though, we can't help but conclude that the moment you choose to use a smaller image size with the SD1, you discard its greatest strength and therefore the most compelling reason to buy the camera in the first place, i.e. its impressive low-ISO detail resolution.