| Foveon’s General Manager, Shri Ramaswami, and Vice President of Applications, Rudy Guttosch, were in the Netherlands for a day, which gave me the opportunity to speak with them. “When we talk in photography about image quality, then we’re talking about Realism. At Foveon, we believe that photography distinguishes itself from other art forms in that it’s capable of showing a scene as faithfully to nature as possible. With increases in sensor resolution, pictures are becoming more realistic. Contrast and micro-contrast contribute to that.” That’s how Shri began. | |
Progress through daring choices |
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Daring choices sometimes lead to revolutionary changes. At the beginning of digital photography, camera manufacturers were convinced that only expensive CCD sensors were suitable for high-quality shots. CMOS sensors delivered too much noise. Canon at that time made an unorthodox choice, to correct the noise of a CMOS sensor per pixel. With that, Canon developed a lead over other camera brands, because Canon could spectacularly lower the production costs of a good digital SLR camera. Currently, all SLR cameras and compact system cameras are equipped with CMOS sensors. The current CMOS sensors are not perfect in terms of recording color. Each individual pixel of a CMOS sensor registers only 1 color: red, green or blue. Because our eyes are more sensitive to green than to red or blue, camera sensors are fitted with just as many green pixels as red and blue together. A 36-megapixel sensor thus contains 18 megapixels green, 9 megapixels red and 9 megapixels blue. That perfectly matches how the human eye registers color, but it doesn’t always work at the detail level. At Foveon, they are convinced that this makes a picture less natural than with a sensor where each pixel records all colors. That has to do with the feeling that you get when looking at a photograph. You can’t always explain why one picture looks more natural, more realistic than another. Even so, you see the difference. Is the time ripe for a new daring choice? |
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Shortcomings of CMOS sensors |
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| On CMOS sensors in modern cameras, the pixels are spread over the sensor in a particular pattern, the Bayer matrix, which you see shown here. To deliver a color shot, each pixel of a CMOS sensor peeks at the other two colors of the neighboring pixels. That works very well: modern digital cameras deliver an image quality that we did not think possible a few years ago. But it can also go wrong. If you photograph a fine-woven fabric that is pure red or blue, then a 36-megapixel camera has just 9 megapixels that register the image. In the case of pure red fabric, you see nothing from the green and blue pixels (3/4 of the total number of pixels). Happily, we almost never encounter pure red or blue fabric in practice. |  |
Another disadvantage of CMOS sensors with a Bayer matrix is the introduction of color moiré. In the photographing of very fine pattersn, with CMOS sensors an interference pattern arises with false colors that don’t really exist in practice. Thanks to low-pass filters and/or software correction in digital cameras, you rarely find visible color moiré in practice. Even so, it would be nicer if you didn’t need to sharpen your pictures at all or have to remove false colors. The less software comes into play, the more natural the image. |
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Foveon: (in theory) better than CMOS |
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At Foveon, a natural image is the primary focus. That’s why Foveon has made a radically different choice in sensor design. Every pixel of a Foveon sensor sees all colors and consists of 3 layers with different color sensitivity. The pixels on a Foveon sensor don’t need to peek at the colors of surrounding pixels—with a more natural image as the result. Shri Ramaswami explains that in the past, Foveon oversimplified that by stating that there were blue, green and red layers. In fact, each of the 3 layers is panchromatic: they register all colors, but in different ratios.
The disadvantage of 3 light-sensitive layers on top of each other on one pixel is that there is little light left over for the lowest layer—with a bad signal-to-noise ratio as a consequence. Pictures made with the Sigma Merrill cameras devilver really beautiful images, as long as you’re limited to low ISO values. Above 400 ISO, the noise becomes a spell-breaker. Foveon has significantly improved the signal-to-noise ratio of the Quattro sensor in comparison to the Merrill sensor. Shri Ramaswami emphasizes that the new Foveon sensor also shows more noise at high ISO values than traditional CMOS sensors. With that, he begins the explanation of how Foveon succeeded in improving the signal-to-noise ratio of the sensor. |
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Foveon X3: radically different |
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The Sigma Quattro sensor consists of 3 layers, of which the upper layer consists of 19.5 megapixels, and the middle and lower layers each have 4.88 megapixels. All 3 of the layers absorb all colors, but in different ratios. That is shown in the picture below with a blue, green and red layer. The Foveon Quattro registers just as many colors as the human eye, and does that in 14 bits. That ensures a very natural tone scale. In order to get the maximum possible benefit from this, a good monitor, a good printer, and good color management are obviously needed. Most of us (still) use a monitor that is not capable of showing all the colors that the human eye can see. That means it’s possible that you only see a color difference in print, while on the screen there was no visible difference. But never mind. The camera’s processor puts all the information in a 19.5-megapixel RGB picture. With this, the Foveon Quattro sensor delivers a 16% higher resolution than the previous Foveon sensor, accurate color reproduction and a better signal-to-noise ration than the previous version of the Foveon sensor, the Sigma DP Merrill. Because all 19.5 megapixels include complete color information, there is no sign of color moiré and the detailing of red and blue subjects is remarkably better than with a CMOS sensor that is used in a system camera or an SLR camera. According to the gentlemen from Foveon, the resolution of a 20-megapixel Foveon Quattro sensor compares with the resolution of a 39-megapixel Bayer sensor. |
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Camera with lens: Sigma dp2 Quattro |
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The quality of a sensor only comes into its own when you use at least an equally good lens with it. Another daring choice is that the Sigma Quattro sensor is only delivered with a fixed lens, which is perfectly aligned with and matched to the sensor. If you want to photograph at another focal length, then you buy another Quattro camera. Soon the Sigma dp2 Quattro will be released: the first luxury compact camera with a fixed, 30-mm lens and a 20-megapixel Quattro (Foveon X3) sensor. The field of view of this combination compares with the field of view of a 45-mm standard lens on a camera with a full-frame sensor. The DP2 Quattro is thus an obvious camera to release first. The Sigma DP2 Quattro is a mirrorless camera, with which you use Liveview for focusing. Both the lack of mirror and the focusing on the basis of the sensor signal make positive contributions to the final sharpness. Flash synchronization is possible to 1/2000 of a second, meaning you can keep photographing at full aperture for longer. In comparison to an SLR camera, with a flash synchronization of 1/250 of a second, that saves 3 stops! By limiting the fastest shutter time to 1/250 of a second, with the use of a fill flash you’ll be forced to stop dwn. The difference in bokeh between a flash-picture at f/2.8 and 1/2000 of a second or one at f/8 and 1/250 of a second is enormous. |
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| Sigma is aiming with this camera for the quality-conscious photographer who wants to have a compact camera with uncompromising quality. At the press conference in Houten, Shri and Rudy showed different prints that were made with the Sigma DP2 Quattro. The prints were more than a meter in size and really lifelike. The image quality is clearly impressive. And the bokeh looked great in the shots that were made at full aperture. |  |
| Where the full-frame sensors of the Nikon D800E and the Sony A7R medium-format cameras compete for the crown, Sigma is now doing that with an APS-C camera. Is this an advancement that’s owed to the daring choice by Foveon to produce a revolutionarily different kind of sensor? Will Foveon X3 become the new benchmark for images faithful to nature? I’m curious. | |
