CMOS Sensor & the MegaPixel Race.......

Yes... u r right... am referring to the Digital Still Cameras (DSC) here... So does the title make u think what the relation is between CMOS sensor and the MegaPixels ?? Well..... there is a very strong relation between the two... Megapixels is to DSC as CPU Speed is to Computers. Both of these are a measure of quality & expected throughput of the system.

Now coming to the topic of MegaPixels.... suppose you see two cameras from two vendors with same MegaPixels, how do u compare them ? are they both same in terms of quality of picture they can produce ? They may or may not be same..... other features of the DSC can help us determine which is the best. CMOS Sensor used in the camera is as vital as the MegaPixels itself in defining the quality of image, the gradations, resolution, dynamic range etc. Lets see how...

CMOS Sensor is that part of the camera which captures the light and converts it in the form of digital image. So naturally more the amount of light is captured, better the quality of image it produces. CMOS Sensor is made of silicon, hence it is called as "silicon eye" also. On the top layer we can find the micro-lenses and below it the pixels. Each pixel is made of light capturing element or bucket, a photo diode and some circuitry.

If you see the below arrangement, C stands for circuitry, P stands for microlens and photodiode. This is how the CMOS sensor will appear. Every C, P pair corresponds to 1 pixel.

CMOS Sensor => |CP|CP|CP|CP|CP|CP|CP|CP|CP|CP|

As we started with the example of 2 cameras with same MegaPixel ratings, lets how they can be different. In the below representation, in camera 1, the CMOS sensor has a larger circuitry size than compared to the micro-lense & photodiode size. So the amount of light it can capture is less, which means signal to noise ratio is small. However in case of camera 2, micro-lense size is larger, and the circuitry size is squeezed..... though there are same number of pixels as in case of camera 1. This will enable higher light capturing efficiency, and hence better signal to noise ratio.

Camera 1 => |CCP|CCP|CCP|CCP|CCP|CCP|CCP|CCP|CCP|CCP|

Camera 2 => |CPP|CPP|CPP|CPP|CPP|CPP|CPP|CPP|CPP|CPP|

At the same time the overall size of the CMOS sensor can also be made larger inorder to increase the pixel bucket size or the P size. This again results in better image quality. So always look for the CMOS sensor size along with the MegaPixel ratings..

My camera [Canon EOS 350D] specs are.... 8 MegaPixel and CMOS Sensor size is 22.2 x 14.8 mm