Capturing razor-sharp and colour-accurate photos can
be a challenge, even with today’s multimillion-pixel digital cameras. But Foveon, an image-sensor company, promises to change all that with its much-anticipated Foveon X3 sensor. This is supposed to yield sharper photos with truer-to-life colour than existing technologies can deliver.
But in our tests of the 3.4-megapixel Sigma SD9, the first digital camera equipped with X3, we obtained mixed results. Images were sharp, but colour accuracy varied. We compared the Sigma’s images with output from the highly regarded £1,494, 6.1-megapixel Nikon D100. We shot images at the cameras’ highest resolutions – 2,268-x-1,512 pixels for the Sigma, and 3,008-x-2,000 for the Nikon. Both are digital SLR cameras intended for professionals, and buying either one counts as a serious investment – especially since the prices don’t include lenses (from £300 to £500).
At the heart of the Sigma SD9 is the Foveon X3 image sensor. The X3 uses a new method for capturing information on a digital camera: every pixel has three layers of photo detectors, each of which senses one of the three primary colours of light – red, green, or blue.
Foveon’s X3 then uses the data from these three layers
to re-create the actual colours of the image.
Current digital cameras use either a CMOS (complementary metal-oxide semiconductor) or – more commonly – a CCD (charge-coupled device) sensor whose pixels have one layer of photo detectors. To capture colour information, a filter for one of three colours (red, green, or blue) is placed on top of the pixel in a grid that looks like a three-colour checkerboard. By measuring the red, green, and blue levels in three or more adjacent pixels, the camera calculates the original colour. In some cases, the method a camera uses to interpret this data leads to artifacts and loss of detail in pictures – problems we’ve seen in many of our test images using cameras with a CCD or CMOS sensor.
In theory, the Foveon X3’s approach, which offers three times the RGB information, should lead to a far
better looking picture than existing technologies can provide.
The theory proved true – at least where sharpness was concerned. The images captured with the pre-production Sigma SD9 maintained their crisp edges both on screen and in print, even at 150 per cent magnification, while photos taken with Nikon’s D100 appeared a tad blurry when magnified to this value.
Moreover, the SD9 captured fine details on an assortment of greyscale bars and wheels, as well as B&W text, with minimum colour interference. Other cameras that we’ve tested, including the D100, produced images with varying degrees of colour distortion.
Colour accuracy, however, was another story. Both cameras’ pictures were impressive, but not perfect (see comparison photos, left). In comparing both sets of prints and on-screen images to the real McCoys, we saw that in some tests the SD9 accurately reproduced shades of red and green, but left yellows and oranges washed out.
We processed the images in Auto mode, as recommended by Foveon. The SD9’s images were duller than those of the D100, and their colours didn’t pop out as much. The D100’s images, on the other hand, looked too yellow.
We did find the Nikon camera a little faster at some tasks, as well as more intuitive, making it easier to use. And the Sigma saves images only in the X3’s proprietary X3F format, which Photoshop can’t read. You must convert the X3F files to either JPEG or TIFF format using the cumbersome Sigma Photo Pro bundled software (which was developed by Foveon) before you can open them in other applications.
Overall, the SD9 produced some good images and some bad. Variations in colour, detail, and sharpness involve multiple factors: camera, lens, software, accuracy of colour calibration between monitors and printers, and even the human eye. If you spot a flaw in an image, figuring out the cause of that imperfection can be extremely difficult.
Digital SLR cameras such as the Sigma SD9 provide a great deal of manual control, however, so users can capture the best possible picture. Although our tests indicate that both Foveon and Sigma still have work to do in improving performance and usability, if you’re willing to tweak, you can enhance your results and enjoy sharper pictures now.
But to ensure that they get the most for their money, many users are probably better off waiting until a few more firmware upgrades are released. Don’t expect to see Foveon’s sensor in cameras from big-name vendors in the near future, either; companies such as Nikon and Olympus are watching, but have made no announcements.