Why does a sensor have unused (masked) pixels.

Submitted by Rich Parry on

Forums: 

One of the RD preferences allow the user to see "Masked Pixels". Why does the sensor have unused pixels, the nerd in me wants to know.

I shoot with Canon cameras, do all sensors have unused/masked pixels?

Thanks in advance,

Dear Sir:

Submitted by lexa on

Dear Sir:

Masked pixels are masked from coming light, so they produce signal level corresponding to complete dark at current conditions (sensor temperature, power level, etc). So, data readed from these pixels may be used as a very good 'black level estimation'.

Also, if multi-channel Analog-to-Digital conversion is used (most today cameras), it is possible to estimate ADC channels difference and, as a result, do banding suppression (for banding caused by ADC channels difference).

AFAIK, all modern Canon cameras have masked area (and this data is used in all LibRaw-based products, including RawDigger, to estimate per-channel black level)

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