7. The Foveon sensor: seeing color like the human eye
SIGMA’s Foveon sensor was named after the Fovea Centralis, the part in the human eye with the highest sensitivity to visual stimuli. Richard Merrill, one of the inventors of the sensor, chose the name to symbolize Foveon’s goal: to create a sensor that can ‘see’ the world just like the sharpest part of our eye.
Digital color information is categorized into primary, secondary and tertiary colors. The three base colors (red, green, blue) of the RGB color model are primary colors. Any color created as a mix of two of these is called a secondary color, and tertiary colors require a mixing of all three primary colors. The human eye sees the world entirely in tertiary colors. Thanks to its vertically stacked photodiodes, the Foveon sensor ‘sees’ visual information in tertiary colors right from the start, and is thereby able to read colors in continuous (i.e., gapless) gradations. Bayer sensors only have one layer to read visual information; they use filters to separate color information into primary colors and then use these to mix the more precise secondary and tertiary colors. This approach is the exact opposite to SIGMA’s, which works with tertiary colors from the start.
In this illustration, I have tried to visualize the journey of light (which is a form of electromagnetic radiation) all the way to the printed product. In principle, SIGMA’s Foveon sensor receives images by sensing light the same way the human eye does. Bayer sensors, in contrast, use digital RGB data as its starting point. This is a fundamentally different approach.
8. The Foveon sensor and continuous color information
Thanks to the vertically stacked photodiodes of the Foveon sensor, it is able to read colors without filtering them first, and as a result there are no gaps (blank space) in the color information saved by the sensor.
To understand what this means for actual images, let’s have a look at Nobuyoshi Araki’s photobook “Shakyo Rojin Nikki: Yoko no Meinichi” (published by Wides Shuppan in 2015; digitized by Shigeru Nishikawa). The photographs in this photobook were digitized by shooting photographic prints with a Foveon-equipped SIGMA camera. In the resulting digitized images, the gradients of each photograph look very clean and natural, even if we zoom in until we can see individual pixels. For comparison, I have added a version of the same photograph that was digitized using a flatbed scanner (with Bayer sensor).
As you can see, when scanning with a Bayer sensor the gradation is nowhere near as clean. This test was done by Shigeru Nishikawa, who digitized the photographs for the photobook, using an industry-standard flatbed scanner. You would expect a high image quality with these conditions, and yet there is no continuous feel to the gradients.
Next, allow me to share a photograph I have taken with a SIGMA dp0 of a stack of boxes of Japanese mandarine oranges (I’ve taken this photo in Uwajima, famous for its mandarine oranges). Even at 5x magnification, the details on the boxes remain clean, without any visible Moiré. Thanks to the Foveon sensor’s continuous gradients, the image can be enlarged beyond what you would expect from its megapixel count.
9. The Foveon sensor’s color space
The Foveon sensor’s RAW data saves color information in a three-dimensional space. I’ve tried to ask SIGMA about details of their method but they wouldn’t tell me. To be fair, it’s probably best for them to keep their trade secrets secret.
However, we can try to understand the principle behind the Foveon’s color space if we take a look at the well-known CIE LAB color space.
In the CIE LAB method, colors are defined using two axes (A and B) that express color in combination with a perpendicular L axis (“L-A-B”) to express lightness. In short, each color in the CIE LAB system is marked within a three-dimensional coordinate system. SIGMA’s RAW data uses a similar color space to save the color information of each image. Behind each color in a photograph hides a three-dimensional information space that defines it with high precision.
Let’s turn our attention towards “Color Photos of the Ancient Ruins” (Tokyo Ancient Orient Museum, 2015). These are color photographs taken by explorer Asashiro Saegusa during an archaeological expedition by Tokyo University to Iraq and Iran in 1955 and 1956, led by Namio Egami.
Saegusa shot the photographs on color slide film — unfortunately, the originals have suffered severe discoloration in the more than 60 years since their creation. Luckily, in 1981, photographic prints were created that still remain today. Using these prints as a calibration standard, Hokkaido-based printing company iWord have done their best to digitize and restore the faded colors of these photographs to their original glory with the Foveon sensor’s unique powers. This case also serves as an example of the astounding permanency of printed matter.
How is it possible to restore the faded colors of reversal film with such dynamic results?
If we were to correct the colors of a photograph using Photoshop, we would have to fix each individual element of the image bit by bit — a time-consuming task. Furthermore, during this process the arbitrary choices of the person in charge would throw off the balance between details and the picture as a whole, and thereby affect the integrity of the image.
But if we think of the colors’ fading as a simple slip within the three-dimensional color space, then we are able to adjust the discoloration (after digitizing the picture with SIGMA’s Foveon sensor) and can restore the image without any damage to its original color balance.
10. Capturing the unpredictable textures in nature and
The natural world knows many textures and substances that defy expectation. How do we capture the finer details of such surfaces and natural materials? Go Itami will share his experiences with this subject in the second talk, but until then I’d like to offer a different angle.
This is the photobook “Kannagara” by Japanese master photographer Issei Suda (published by Place M in 2017; digitized by Shigeru Nishikawa). For the digitization process of the images, Issei Suda was asked to provide the original monochrome negatives which were placed on a light-table and photographed with a SIGMA camera and macro lens.
When making gelatin silver (i.e., black-and-white) photographic prints, inevitably the prints will contain less visual information than the negatives used to create them. However, by digitizing an image straight from the negative, it is possible to capture the original photograph with all its fine gradations and details still intact.
In this picture, for example, we are able to discern the luminous element of the flashgun used in the photograph — even though it was not visible at all in the original photographic print. That is because the luminous element of a firing flash is, so to speak, a “white spot surrounded by white”. But when we look at the photograph’s negative with a SIGMA camera, suddenly this unexpected detail becomes visible. Black-and-white (silver halide) negatives record more visual information than the human eye can see, and SIGMA’s sensor will extract that information ruthlessly. With the Foveon sensor, finally we have a match for the unpredictable depths of silver halide film.
I have one more example to show you. It is a comparison between two photobooks: “Basho (Location)” (published by Banseisha in 2000) and “@aum” (Pot Shuppan, 2015), both photographed by Yoshiaki Koga at former training facilities of the Aum Shinrikyo sect.
“Basho” is old enough still to have been digitized using a drum scanner (see chapter 4), while the newer “@aum” was digitized with a Foveon-equipped camera. Both digitization processes were handled by Shigeru Nishikawa. There are a number of photographs that appear in both series, and when we compare these images, we are allowed a first-hand experience of the difference between the capabilities of drum scanners and the Foveon sensor.
In one particular photograph in the “@aum” series, we are suddenly able to see stars in the night sky that were not there in the photographs “Basho” counterpart. The general sense of depth, too, is dramatically different in both series. Here, again, the Foveon sensor proves its ability to capture the true image, as recorded by the silver halides in photographic film.
11. Expressing depth and three-dimensionality
When creating a photobook, what are the aspects most worthy of your attention? The two most important elements to care about are tone and gradation. If you get these two right, you will be able to express a sense of depth and three-dimensionality. Printed matter is, by nature, a two-dimensional medium. But printing technology has made incredible advances in order to surmount the paradox of expressing depth and perspective on a flat page. Ever since Gutenberg’s printing press, humankind has been looking for ways to show within a flat surface the world in its multiplicity and three-dimensionality.
Continuous, detailed gradients and colors are necessary to give images a spatial feeling, and SIGMA’s Foveon sensor has shown itself an incredible tool to record continuous image tone information, both when creating new photographs and when digitizing existing ones.
I would be very happy if my presentation helped demonstrate the ability of SIGMA’s cameras to produce and digitize images with unprecedented clarity and precision.
Born in Tokyo in 1950. Edited the critical design magazine d/SIGN together with Tsutomu Toda (2001-2011). Visiting scholar at the Kobe Design University. Book publications include “Gamen no Tanjou (‘The Birth of Images’)” (2002), “Pe-ji to Chikara (‘Page and Power’)” (2002), “Juuryoku no dezain (‘The Design of Gravity’)” (2007), “Dezain no Tane (‘The Seeds of Design’)” (together with Tsutomu Toda, Japanese, 2015), “Zettai Heimentoshi (Plane City)” (together with Daido Moriyama, 2016), “The Life and Views of Book Designer Hitoshi Suzuki” (Japanese, 2017) and more.