CCD vs CMOS, Which One is Better?

Every digital camera has at its heart a solid-state device which, like film, captures the light coming in through the lens to form an image. This device, called a sensor. An image sensor is a device that converts an optical image into an electronic signal. It is used mostly in digital cameras and other imaging devices. Early analog sensors were video camera tubes, most currently used are digital charge-coupled device (CCD) or complementary metal–oxide–semiconductor (CMOS) active pixel sensors.

CCD vs CMOS

As you may have know, today, most digital still cameras use either a CCD image sensor or a CMOS sensor. 

A CCD image sensor is an analog device. When light strikes the chip it is held as a small electrical charge in each photo sensor. The charges are converted to voltage one pixel at a time as they are read from the chip. 

A CMOS image sensor is a type of active pixel sensor, made using the CMOS semiconductor process. Extra circuitry next to each photo sensor converts the light energy to a voltage. 

Both CCD and CMOS have their own advantage in creating image quality. CCD sensors are more susceptible to vertical smear from bright light sources when the sensor is overloaded; high-end frame transfer CCDs in turn do not suffer from this problem. On the other hand, CMOS sensors are susceptible to undesired effects that come as a result of rolling shutter. But, more importantly, CMOS sensors are less expensive to manufacture than CCD sensors and consume less power, thus helping camera batteries live longer.

Because of the manufacturing differences, there have been some noticeable differences between CCD and CMOS sensors.

• CCD sensors create higher quality images and lower noise images than CMOS sensors. CMOS sensors on the other hand, are more susceptible to noise.
• Because each pixel on a CMOS sensor has several transistors located next to it, the light sensitivity of a CMOS chip tends to be lower.
• CMOS traditionally consumes little power. On the other hand,  CCDs consume as much as 100 times more power than an equivalent CMOS sensor. Simply said, camera batteries will live longer in CMOS based camera than CCD based camera
• CMOS chips can be fabricated on just about any standard silicon production line, so they tend to be extremely inexpensive compared to CCD sensors.
• CCD sensors have been mass produced for a longer period of time, so they are more mature.

Based on these differences, you can see that CCDs tend to be used in cameras that focus on high-quality images with lots of pixels and excellent light sensitivity. CMOS sensors traditionally have lower quality, lower resolution and lower sensitivity. CMOS sensors are just now improving to the point where they reach near parity with CCD devices in some applications. CMOS cameras are usually less expensive and have great battery life.

 

Foveon X3 sensor

Foveon X3 is based on CMOS technology and used in Sigma's compact cameras and DSLRs. The Foveon X3 system does away with the Bayer filter array, and opts for three layers of silicon in its place. 

Shorter wavelengths are absorbed nearer to the surface while longer ones travel further through. As each photosite receives a value for each red, green and blue colour, no demosaicing is required.

 

LiveMOS sensor

LiveMOS technology has been used for the Four Thirds and Micro Four Thirds range of cameras.  LiveMOS is claimed to give the image quality of CCDs with the power consumption of CMOS sensors.

Sensors and Pixels

At one point it was necessary to develop sensors with more and more pixels, as the earliest types were not sufficient for the demands of printing. That barrier was soon broken but sensors continued to be developed with a greater number of pixels, and compacts that once had two or three megapixels were soon replaced by the next generation of four of five megapixel variants.

More pixels can mean more detail, but the size of the sensor is crucial for this to hold true: this is essentially because smaller pixels are less efficient than larger ones. The main attributes which separate images from compacts and those from a DSLR are dynamic range and noise, and the latter type of camera fares better with regards to each. As its pixels can be made larger, they can hold more light in relation to the noise created by the sensor through its operation, and a higher ratio in favour of the signal produces a cleaner image.

The increased capacity of larger pixels also means that they can contain more light before they are full - and a full pixel is essentially a blown highlight. When this happens on a densely populated sensor, it's easy for the charge from one pixel to overflow to neighbouring sites, which is known as blooming. By contrast, a larger pixel can contain a greater range of tonal values before this happens, and certain varieties of sensor will be fitted with anti-blooming gates to drain off excess charge. The downside to this is that the gates themselves require space on the sensor, and so again compromise the size of each individual pixel.