MEGA PIXELS & IMAGE SENSOR SIZE And their effect on image quality

 The image sensor. A camera's lens projects an image on the surface of an image sensor. This surface is pretty small and a collection of millions of separate sensors. Each sensor is like a solar cell, producing an analog electrical signal that is then converted into a digital value. All these values together make the photo. MegaPixels. The more pixels on the image sensor, the more details a picture can have. We want sharp pictures, so we need lots of pixels; MegaPixels. One MegaPixel = 1,000,000 pixels. But how many MP is enough? For high quality snap shots, 8 MP is more than enough. Photographers may need much more pixels depending on what they are working on. For many professional jobs 8 MP is fine too, as long as the pixels are quality pixels. To double the resolution of a 1 MegaPixel sensor, the amount of pixels both length and width must go times two! So: 4 MegaPixels is double as sharp as 1 MegaPixels. To double the resolution, the amount of MegaPixels must be times 4 To double the resolution of a 4 MegaPixels sensor, you'll need 4*4 = 16 MP To double the resolution of a 16 MegaPixels sensor, you'll need 16*4 = 64 MP To double the resolution of a 64 MegaPixels sensor, you'll need 64*4 = 256 MP So, when having an 8 MP camera, buying a 10 MP camera will not give you much sharper pictures, you'll probably not notice the difference.

 The picture above shows how much the image sensor sizes differ in digital photo cameras. Most compact cameras have tiny sensors, with too many pixels, and are therefore not able to produce good quality pixel data, especially in low light situations. "Full frame" sounds like the biggest possible sensor, but there are bigger ones. The size is equal to the by now old 35 mm film format: 24 x 36 mm. It's called 35 mm because that's how wide the film rol was cut. I once had an analog 8 * 10 inch camera, 203 * 254 mm, THAT is big. What is called "Full frame" today, used to be the smallest option in the last years of analog photography.

Examples:
 Type Size example MP MP/cm2 Full frame 36 x 24 mm Canon EOS 5D Mark II 21 2.4 APS-C (Nikon DX) 23.1 x 15.4 mm Nikon D7000 16.2 4.6 Micro Four Thirds 18 x 13.5 mm Panasonic Lumix DMC-G2 12.1 5 1/1.6" (1/1.63") ±8 x 6 mm Panasonic Lumix DMC-LX5 10.1 24

 MISSING PIXELS

 Because a 10 MP camera produces 10,000,000 RGB pixels, and every pixel contains color information from 1 location, one would expect there to be: 10,000,000 Red sensors 10,000,000 Green sensors 10,000,000 Blue sensors All together 30,000,000 sensors (3 sensors in the same location) But in reality, there are only: 2,500,000 Red sensors 5,000,000 Green sensors 2,500,000 Blue sensors That's all together only 10,000,000 color sensors.. There are 20,000,000 color sensors missing!! The missing 20,000,000 measurements are simply 'predicted' (guessed). 2/3 of a typical photo's data is made up... Why? Because most digital cameras have a "Bayer filter arrangement" in front of the image sensor, arranged like the picture below (the colors show to what color the area is sensitive):

 In every block of 4 cells, there are: 2 sensitive for Green, 1 for Red, and 1 for Blue. This explains why the green channel often has the highest quality. Each Bayer-MegaPixel sold to us, should produce only 0.25 MegaPixels, so that for every RGB pixel, there is at least 1 sensor for each color. And one more thing: because each cell in only sensitive for 1/3 of the visible spectrum, 2/3 of the light and image information is wasted! Now go out and shoot some cool photos!

 Giesbert Nijhuis