The Foveon against attack ... Sony?

The rumor for months on forums and other specialized blogs regularly resurfaces: Sony would work on Foveon sensor types. The father of the Nex and Alpha and seems to take over and in its way, a technology exclusive sensors Sigma today. In order to understand the issues behind these rumors, a review of troops is necessary.

Who?

This is Sony.

And Foveon?

This is an American company bought in 2008 by Sigma, forming a strictly independent multidisciplinary duo giant Nippon (aka Sony). By abuse of language, the name of the brand has become one of the sensor (code name X3), the name of the sensor technology, the technology becomes gradually turn myth, grail, a demonstration exotic unique know-how (though in fact not, we shall see below), or simply an unusual photographic curiosity (this means it has a certain charm and endearing but there are gaps in preventing to impose on a large scale). So he should write Foveon ® or in our case today, and because it must try to live with the times, we talk about Foveon sensors like or Foveon technology.

What is special about this technology?

To distinguish the exception, we must remember the general rule. On all sensors, all devices capable of taking pictures, the photosites derive their ability to distinguish colors because they are covered with a color filter (Red, Green, Blue) which prémâche their work. Before demosaicing, interpolation and long before the mill processor, so each pixel has only one color component (depending on the filter he had on his head). And this is true for CCD, CMOS, lit, backlit, the filter is Bayer (so everyone except Fuji) or XTrans (Fuji way, except everyone). Foveon sensors like, them, do not use filter (colored)! They are based on quantum properties of silicon (material that are made sensors and microprocessors, in fact, the very sandy, very, very clean and worked).

Um, quantum properties?

Do not go, it has not complicated. Silicon is a semiconductor capable of converting electromagnetic waves into electrical current. However, light is an electromagnetic wave, so the sensor converts light into electricity. Foveon sensors like go much further: silicon reacts to electromagnetic waves differently depending on its thickness. In fact, theoretically, a sliver of silicon is able to distinguish between blue, green, red in thickness and in that order.

The consequences?

Need to filter the photosites, so everyone can individually register the three colors, resulting in an almost total elimination of color artifacts in the final image. In addition, since no color filter lets you see only one color, it also means that each photosite only receives one third of the incident light. The second benefit of the disappearance of the color filter is a theoretical increase in sensitivity. It is, for example, what happens on the Leica M Monochrom: removing the Bayer filter, the German digital rangefinder camera made a leap in sensitivity (almost two IL). It is usually at this point that their happy owners realize they have a Foveon like, but do not see colors.

So, if everything is so beautiful and everything is so much better, why not everyone does him likes Foveon?

For two reasons all animals: long, nobody believed him. Foveon (the company), like many small innovative companies, has knocked on many doors remained closed desperately (including Hasselblad, for example). Only Sigma has believed in it since 2008 enjoying a right of exclusive use of the technology. Ouch problem. Second obstacle: the theory is nice, the practice is better. However, according to Paul Valéry "everything that is wrong is simple, everything that is not useless" tame the silicon so that it is capable of perceiving and especially distinguish and marring the blue, green and red individually, it is a challenge that requires a high level of technical and very important ways. And this is where Sony comes in!

Sony will he buy Sigma Foveon?

Not. A thousand times no. Sony has decided to opt for elegant from scratch and developing its own technology. After all, it is not because Sigma Foveon has some technology patents that silicon will suddenly stop to distinguish colors. With this truism, Sony is working very hard to improve its sensor since at least 2009. The curious may consult directly with several patents here, here, here, and here. It is especially the latter that interests us as dated January 10, 2013.

This patent describes various options and alternatives for the internal structural organization of photosites, with a recurring pattern: from the surface to the "depths" is the blue component first, then green, then red, in this effect, which is captured. Logical path as consistent with the visible light spectrum, lower wavelengths at higher.

What Sony sensors they are distinguished?

What we teach US20130009263A1 patent is a Foveon like a very good sensitivity across the entire visible light. Problem? It is very complicated to design photosites capable, in their thickness, perfectly distinguish each primary color from each other. For example, for a wavelength of 550 nm (corresponding to a green vest assistance, or the color that the human eye is most sensitive), the photosite cannot see that it is green bright, but a half-and-half mixture of green and red. In other words, the orange. It is easier to see with a chart directly from the patent:

Sony and offers multiple options for the internal structure of its photosites. Many variations that recall some publicity for a sandwich, the place upside, above, from below, with individual discharge circuits, shared ... In the midst of these, appears even a hybrid solution using a matrix-color filters:

And yes. This is a mosaic of color filters; even though we explained that the interest of Foveon sensors was like not to be used. So why technical choices from Sony? Small optical recall. The magenta is complementary to green, and vice versa. A green filter passes only the green light and blocks the rest, so a magenta filter blocks green light and passes the blue and red. The underlying idea? Rather than using photosites able to discern the three colors, use photosites are distinguished as green (under the green filter) and photosites not distinguishing the blue and red (in magenta filters). In short, the best of both worlds: minimizing color artifacts and better color discrimination. To see if the final solution adopted by Sony retain this option.

What is (was) the interest to the end user?

If Sony achieves its research and technology markets its new home, it will prove first that Foveon (and Sigma) held excellent developing sensors. In terms of results, we can expect a quantum leap in color rendering (loyalty, reduced chromatic aberration, reduced artifacts), in terms of sharpness (great progress in terms of aliasing) and in terms of definition. The same number of photosites provides superior image quality, so no need to further reduce and even their size (which will very soon reach a critical threshold). With the industrial power of Sony, sensors like Foveon can finally get rid of their current biggest flaw, namely poor performance in high sensitivity.

Many beautiful promise so we are rumors. In Digital, we are in favor of such a move, and expect to firm up that all this is reflected in the near future, for better photography. We already have the mouthwatering.