Mixed Verdict on Photo Sensor
Capturing razor-sharp and color-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, which is supposed to yield sharper photos with truer-to-life color than existing technologies can deliver.
But in our tests of the 3.4-megapixel Sigma SD9 ($1800), the first digital camera equipped with X3, we obtained mixed results: Images were sharp, but color accuracy varied. We compared the Sigma's images with output from the highly regarded 6.1-megapixel Nikon D100 ($2000). We shot images at the cameras' highest resolutions--2268 by 1512 for the Sigma, and 3008 by 2000 for the Nikon. Both are digital single-lens reflex cameras intended for professionals and advanced hobbyists, and buying either one counts as a serious investment, especially since the prices don't include lenses (from $400 to $600) or memory cards ($70 for a 128MB CompactFlash card).
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 colors of light--red, green, or blue. Foveon's X3 then uses the data from these three layers to re-create the actual colors of the image (see "How It Works," below).
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 color, a filter for one of three colors (red, green, or blue) is placed on top of the pixel in a grid that looks like a three-color checkerboard. By measuring the red, green, and blue levels in three or more adjacent pixels, the camera calculates the original color. 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 preproduction Sigma SD9 maintained their crisp edges both on screen and in print, even at 150 percent magnification, while photos taken with Nikon's D100 appeared a tad blurry when magnified at 150 percent.
Moreover, the SD9 captured fine details on an assortment of gray-scale bars and wheels, as well as black-and-white text, with minimum color interference. Other cameras that we've tested, including the D100, produced images with varying degrees of color distortion.
Color accuracy was another story: Both cameras' pictures were impressive but not perfect (see comparison photos, below). 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 colors 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 common image editing programs such as Adobe 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 and the D100 each produced some good images and some bad. Variations in color, detail, and sharpness involve multiple factors: camera, lens, software, accuracy of color 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 like the Sigma and Nikon 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 pics 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; companies like Nikon and Olympus are watching it but have made no announcements.
