Thursday, June 14, 2012

Crowded Pixels Don't Make a Pretty Picture


Today’s camera brochures and specs  lead us to think that the number of megapixels makes all the difference in the world; like a raucous party - the more the better.  But this isn’t entirely true – in either case. 



The number of megapixels does make a difference, but only up to a point. We need to consider the size of the image sensor. Remember, pixels are photo-receptors etched into the silicon of the image processors. The job of the pixel is to record the photons (light) reflected through the lens. 



We can compare it to a jigsaw puzzle, with each pixel holding a piece or an element of the picture.  


A digital image is made up of numbers, millions of 1’s and 0’s that determine the colors of the composite pixels, their placement, and light intensity.  When digitally processed, each pixel’s signal is interpreted as to color and light intensity and, collectively, processed back into a recognizable image of the captured scene.

Pixel Over-crowding

 More pixels may mean more information but they don’t necessarily mean a clearer image or higher resolution. If you increase the size or the amount of pixels without increasing the size of the sensor the pixels are going to be crowded together and pixel overcrowding leads to digital noise. When pixels are in too close proximity, in some cases, the digital signals of the photons can interfere  with each other, resulting in noise. In other instances, some of  the  light can spill  off the sides of the pixels leading to  image degradation.

Digital Noise

We are not aware of them per se, but electronic signals are being transmitted around us non-stop. If your television is on,  broadcast data is being transmitted over cable or through an antenna. Switch on your car radio and an  audio signal  the transmitter’s station  en route to the cars receiver via the antenna. For digital cameras, the signal is the light that travels through the lens and hits the camera sensor.


No matter what type, some degree of noise is always present in these transmission. In terms of TV when an antenna, rabbit ears or roof,  was the receiver, we experienced noise   in the guise of a “snowy” picture or  visual static. Noise in radio transmission produces a crackling sound often painful to the ear.
When it comes to the digital camera,  noise can affect a video frame in a variety of ways.
It can result in a frame of randomly spaced brightly colored pixels:



It can obscure small features and skew the color


It can result in a lack of clarity in darker areas


One way to combat digital noise in today’s megapixel world is to use larger image sensors while at the same time, improving  image quality.



Larger sensors are a win-win solution:
·         Larger sensors not only hold more pixels  they can hold bigger pixels.  
·         Bigger pixels hold more light.
·         The more light, the stronger the digital signal.
·         The stronger the digital signal, the greater the chance of overcoming the digital noise.
In addition, photosites themselves can be spaced farther apart on a larger sensor, creating less electrical contamination resulting in a stronger signal and less noise from the start; a higher signal to noise ratio.

Signal to Noise Ratio

The term signal to noise ratio is one we come across in electronics, and it’s a good thing. It’s relatively easy to comprehend, A higher signal to noise ratio means the signal overwhelms  the noise,  resulting  in clearer transmission of whatever type of signal is involved. In the case of video, relatively little digital noise translates into better clarity and more detail.
To sum it up, the larger the sensor you have in your camera, the less noise,  greater detail,  and more superior  the image quality you will obtain. But human nature being human nature, although you'll have so much more than you did just a few years earlier, you'll still want more.

Next post –  larger sensors, more dynamic range

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