September 18 2007
Kodak recently announced a major development in digital camera sensor design that allows the capture of more light per pixel for faster shutter speed and better noise performance.
The new sensor from Kodak increases the sensitivity to light from two to four times as much when compared to digital camera sensors in common use today. This is equivalent to raising the ISO setting requiring one to two f-stops less of aperture than is the case with current cameras.
The image senor is the heart of the camera converting light into the electrical signals used to construct the digital image.
The basis for most current digital cameras is the “Bayer Pattern” of red green and blue pixels originally developed by Kodak’s Dr. Bryce Bayer in 1976.
The principle of this design is the use of color filters over the light sensitive receptor sites to give a signal equivalent to each of the three main colors for each point on the image. Combining the ratio of the intensity of the three colors produces an accurate representation of the brightness and color of the light at that point of the image.
The problem is that color filters work by blocking some of the light and only allowing a portion of the light through. For example, a blue filter only allows bluish light through, blocking the red and green sections of the light from a scene.
This produces a lower signal from the sensor and makes the inherent electrical noise large by comparison, the signal to noise ratio. We see noise in our digital images as speckles in darker areas of the image.
Kodak’s new design adds a clear receptor to the sensor array to measure white light. Because it has no colored filter, it collects more light and produces a larger signal resulting in a better signal to noise ratio, or less noise.
The clever bit is that Kodak engineers have developed a method of combining the information from the color receptors with the intensity information from the extra sensor to produce a color digital image.
Noise is increasingly a problem in sensor design for digital cameras as manufacturers seek to increase the resolution of a sensor while keeping the size of the sensor the same. To achieve this, the light receptors in the sensor must be smaller to fit more in the same space. Smaller size receptors mean less light for each individual receptor and a worse signal to noise ratio, so more noise in the images from the camera.
Despite increasing the number of receptors, if Kodak’s new design can provide a greater useable electrical signal from smaller receptors then high-resolution digital cameras will be useable in what are now marginal lighting conditions.