ADC stands for Analog to Digital Converter and refers to the digital camera's ability to capture an image and convert it into a digital file.
All digital cameras are assigned an ADC number and it is given in the manufacturer's technical specifications for each model.
What Is ADC?
All DSLR and point-and-shoot cameras employ sensors that consist of pixels with photodiodes. These components convert the energy of photons into an electrical charge. That charge is converted to a voltage, which is then amplified to a level at which it can be processed further by the digital camera's Analog to Digital Converter (variously called the ADC, AD Converter, and the A/D Converter).
The ADC is a chip inside your digital camera and its job is to classify the voltages of the pixels into levels of brightness and to assign each level to a binary number, consisting of zeros and ones. Most consumer digital cameras use at least an 8-bit ADC, which allows for up to 256 values for the brightness of a single pixel.
Determining the ADC of a Digital Camera
The minimum bit rate of the ADC is determined by the dynamic range (accuracy) of the sensor. A large dynamic range will need at least a 10-bit ADC to produce a large number of tones and to avoid any loss of information.
However, camera manufacturers usually over-specify the ADC (such as with 12 bits instead of 10 bits) so as to allow for any errors on it. Extra "bits" can also help to prevent banding (posterization) when applying tonal curves to data. However, they will not generate any additional tonal information, apart from noise.
What Does This Mean When Buying a New Camera?
The ADC plays a larger role with higher-end DSLR cameras at the professional and prosumer levels. Many DSLRs have the ability to capture with either higher ADC ranging like 10-bit, 12-bit and 14-bit. These higher ADCs are designed to increase the possible tonal values that the camera can capture, creating deeper shadows and smoother gradients.
The difference between a 12-bit and 14-bit image is going to be very slight and may even be unnoticeable in the majority of photographs. Also, it is all going to depend on that dynamic range of your sensor. If the dynamic range does not increase with the ADC, then it cannot be effective in improving image quality.
As digital technology continues to improve, so will the effective image tonal range and the camera's ability to capture it.
In most DSLR cameras, capturing images using any ADC above 8 bits requires shooting in RAW format. JPGs only allow for an 8-bit channel of data.