Direct Image Sensor | SIGMA DP1x : Special Contents

You might be surprised to learn that the sensors in most digital cameras on the market, apart from Sigma’s SD and DP series, are basically monochrome. Because monochrome sensors do not capture color data, a color filter with a mosaic of pixels for the three primary colors – red, green and blue (RGB) – is mounted on top so that color data can be represented. But each light-sensing photodiode has a one-color filter, which means that each pixel can only capture one color, and data for the other two colors is discarded.

Until this stage, of course, as in the Autochrome process, the RGB color “particles”, or pixels, are recorded unmodified, forming the photo. A color interpolation process known as demosaicing is therefore performed in the latter stage of the image processing, and this restores the colors lost by individual pixels. This interpolation process basically consists of guessing the missing colors from the neighboring pixels, and adding them back in.

Having been continuously improved over an extended period, this image-processing method has matured to a certain extent, so the color interpolation is now performed fairly accurately. But because colors are interpolated from neighboring pixels, the subtle color nuances of the original subject are lost.

Conventional digital cameras using color filter arrays also generate color artifacts – colors not found in the original subject – during the demosaicing processing. This is due to the action of the color filter (generally a Bayer filter),

which tries to regulate the color distribution if the subject contains too much detail (high-frequency areas).

A conventional digital camera using a Bayer color filter has yet another filter, known as an optical low-pass filter, interposed between the lens and the sensor, in order to suppress color artifacts. The optical low-pass filter acts on the images resolved at a high level by the imaging lens, its job being to eliminate any detailed elements likely to generate color artifacts (high-frequency areas above a certain level), immediately before they reach the sensor. So it can effectively suppress the generation of color artifacts, but the downside is that it naturally reduces the resolution of the image.

Images produced by Sigma’s SD and DP series cameras have what’s been called an “emotional quality”. This phrase expresses the distinctive image-quality you only get with the Foveon X3® direct image sensor. In terms of clarity and fine detail, it goes far beyond the capabilities of conventional digital cameras. This level of image quality reproduces the scene you shot, right down to the feeling in the air. It’s only possible in a vertical color-capture system that does not require color interpolation, and an image-processing system that does not require an optical low-pass filter.

A conventional image-sensor, on the other hand, fudges the colors, and even cuts out high-frequency areas. To compensate, the sharpness processing is ramped up to give some overall nuancing and a general impression of high resolution. This explains the tendency to generate images that, as a whole, have an unnatural feel. The colors can be adjusted to some extent in post-processing, but the detailed data previously lost cannot be recovered. No wonder the images produced by conventional digital cameras, despite their emphasized edges and clever nuancing, look so unnatural, so subtly wrong, It’s all about basic principles.

The DP1x’s Foveon X3® direct image sensor utilizes the special features of silicon, which is penetrated to different depths by different wavelengths of light, to successfully achieve full-color capture for the first time ever in a single-chip configuration. No color filter is required. Like modern color film cameras, it uses a method that captures all the colors vertically.

Because it does not need color interpolation or a low-pass filter, the X3 image sensor produces images that are sharp right from the start. Therefore, sharpness processing in the latter stages of the image processing – creating edges and emphasizing contours – can be reduced to a minimum. This is why reviewers have evaluated the images captured by the X3 image sensor as having a truly nuanced, sharp feel, and praised them as very natural and demonstrating superior image quality.

The Foveon X3® direct image sensor reproduces pure, rich data and nothing else. The image quality it delivers is breathtaking. You really need to see it for yourself.