Smoke and Mirrors

For those of you who may have an allergic reaction, or break out in hives at the thought of deep tech information you might want to take a pass on today's blog. For you others that have more than a passive interest in how their digital camera function stick around. This may not have any real value in day to day photography but it is pretty cool stuff.

No, this is not a multicolor game of checkers. It is what is termed as a Bayer filter. Back in the day (1975) at Kodak, a Dr. Bryce E. Bayer came up with a way to digitally filter light so a light absorbing diode could register an electrical charge that could be translated into a digital value. Ok, so that was a mouthful and what is with the grid.

I'm glad you asked! I'll save you the time, there are twice as many green filter blocks than there are either red or blue. BTW this is where we get our RGB color gamut. Why is this you ask. The human eye is much more in tune with a green color when it comes to brightness or luminance. Meanwhile red and blue colors react to the human eye better in tonality or chrominance.

Once the light is filtered, the sensor diode receives a charge, is amplified and transmitted to the cameras processor for interpretation. This all happened back in the late 60's by some guys by the name of Peter Noble and Savvas Chamberlain. This is the area that we will focus on next as this is the foundation of out CMOS sensors in most all digital Cameras. Without getting into arrays and how the interact and provide the information to a camera processor we will focus just on the APS or Active Pixel Sensor shown below.

This is where the smoke and mirrors comes into play but is really cool stuff. When the sensor is exposed, light photons strike the sensor and place a charge on the photodiode (triangle above). The specifics of how this all works is greek to me but the process happens something like this.

The transistor marked as MSF amplifies the signal based on the voltage provided by the VDD bus. This amplification provides a much improved quality of information than that of the older sensors that amplified the signal at the end of the array of APS's. The second transistor marked MSEL is what directs the information out on the line to be received by the processor. If anyone id familiar with a computer network and how it handles packets of information will appreciate how this all works. Once the information is dispatched the transistor marked MRST activates and resets the photodiode to a neutral state awaiting the next exposure.

I know what you are asking yourself... Why would I put this information up on my blog when it is so deep into tech. Well it is not necessarily to demonstrate my advanced knowledge because I really am not! It is though a sample of a photographic training presentation I have been working on and this APS was just a couple of slides that I will have available if I need to delve that for into it.

That more or less wraps up today. Take care.

Doug