KEY SENSOR TECHNOLOGI ES
A charge-coupled device (CCD) image sensor uses a global shutter to capture an entire frame in one instance. It is the more mature technology and was used in early digital cameras, but has since been overshadowed by the rise of CMOS sensors in recent years. CCD sensors are prone to vertical smear, where bright lights can create a vertical line from the top to the bottom of the image, but it does not suffer from the rolling shutter effect that plague CMOS sensors.
Backside-illuminated (BSI) sensors move the light-blocking wires on CMOS sensors to the back of the sensor, making them more efficient at capturing light in low-light situations, producing less image noise in the process.
Complementary metal-oxide semiconductor (CMOS) image sensors are the predominant technology used in digital cameras today. It uses a rolling shutter to capture a frame from top to bottom, recording each pixel one-by-one.
With CMOS sensors, additional circuitry can be built onto the sensor to perform additional tasks, like focusing and image-processing. Compared to CCDs, CMOS sensors are more power effcient and cheaper to produce. CMOS sensors however, are prone to the ‘rolling-shutter effect’, which makes the image tilt and distort when capturing video of a fastmoving subject or when panning the camera while shooting.
4 BAYER ARRAY
The photosites on a sensor capture light, but a color lter is required to capture color images. The most common color filters is the Bayer Array, which consists of alternating rows of red-green and bluegreen filters. Bayer demosaicing is the process of translating these primary colors into a full-color image, by deducing each pixel’s color from the value captured by it and its neighbours. However, this process can reduce image resolution, because of the blurring that inevitably occurs when combining capture data.
The Leica M Monochrom is famously known for removing the color lter array entirely, shooting only black and white images. Removing the color lter brings certain advantages, like reducing image noise and increasing ne resolution, as none of the pixels need to be demosaiced.
6 OPTICAL LOW-PASS FILTER
The optical low-pass lter, also known as the AA lter, is found in almost every digital camera. It reduces the appearance or moiré artifacts, which can appear in photographs of repeating patterns, at the cost of blurring of ne detail. The optical low-pass lter is signi cant today, not so much for its inclusion, but its exclusion from cameras like the Leica M9 and the Sony RX1R. By removing the lter, the sensor can capture more ne details.
7 X-TRANS SENSOR
To do away with the optical lowpass lter and reduce the risk of moiré artifacts, FUJIFILM invented the X-Trans sensor, found in its cameras like the X-Pro1 and X100S. Inspired by the random arrangement of ne lm grain, the new array’s RGB pixels are arranged in 6 x 6 pixel sets with a high degree of randomness when compared to conventional sensors. This eliminates the incidence of moiré, as well as resulting in better color reproduction.
5 FOVEON SENSOR
The Foveon CMOS sensor is significantly different from the digital sensors found in most cameras today. Designed by Foveon, the sensor’s photosites consist of three vertically stacked RGB photodiodes. Each photodiode responds to different wavelengths of light, and the resulting data produces the nal color information of the pixel.
Because demosiacing is not required to produce a full-color image, a Foveon sensor doesn’t suffer from the disadvantages of having a Bayer array lter, like loss of detail. The optical low-pass lter is also not needed in a Foveon sensor, which means the sensor can capture a high amount of detail.
However, Foveon sensors can have problems with color accuracy, due to possible color contamination within the stacked photodiodes. Because more light is absorbed by the stacked photodiodes, a Foveon sensor can also be prone to image noise in low-light shooting.
A Bayer Array color filter.