Digital camera part 1

Hmm haven't wrote for the past 2 days... well think today's topic on digital camera should be quite easy for most ppl. As I look through the article, I think there are certainly more than meets the eye...

First, the difference b/n a digital camera and a normal camera. Well, digital camera has a built-in computer which can store images in electronic form rather than rely on chemical and mechanical processes. Instead of focusing light on a film(normal camera), digital camera focuses light onto a semiconductor device. The computer then breaks this electronic info into digital data. Most digi cam use the image sensor known as charge coupled device (CCD). Some low-end cam use complementary metal oxide semiconductor(CMOS) technology.CCD is basically a group of tiny light-sensitive diodes(photosites) which convert photons(light) into electrons(electrical charge). Photosite is sensitive to light, so the brighter the light that hits onto a photosite, the more electrical charge the photosite accumulate.

CCD vs. CMOS Sensors
"Charge is transported across the chip and read at one corner of array. An analog-to-digital converter turns each pixel's value into a digital value. In most CMOS devices, there are several transistors at each pixel that amplify and move the charge using more traditional wires.The CMOS approach is more flexible because each pixel can be read individually. "

• CCD sensors create high quality, low-noise images while CMOS sensors are more prone to noise.
• Light sensitivity of CMOS lower due to the fast that many photons hitting the chip hit the transistor rather than the photodiode.
• CCDs consume as much as 100 times more power than an equivalent CMOS sensor.
• CMOS chips can be fabricated on just about any standard silicon production line, so they tend to be extremely inexpensive compared to CCD sensors.
• CCD sensors have been mass produced for a longer period of time, so they are more mature. They tend to have higher quality pixels, and more of them.

CMOS are less expensive and have a longer battery life than CCD.

The amount of detail a camera captures is called resolution which is measured in pixel. Typical resolutions that you find:

• 256x256 pixels - This is 65,000 total pixels.
  
• 640x480 pixels - This is the low end on most "real" cameras. This resolution is great if you plan to e-mail most of your pictures to friends or post them on a Web site. This is 307,000 total pixels.
  
• 1216x912 pixels - If you are planning to print your images, this is a good resolution. This is a "megapixel" image size -- 1,109,000 total pixels.
  
• 1600x1200 pixels - This is "high resolution." Images taken with this resolution can be printed in larger sizes, such as 8x10 inches, with good results. This is almost 2 million total pixels. You can find cameras today with up to 10.2 million pixels.

There are five ways to capture colours for digital cam.

1. Light is directed to the different sensors by placing a beam splitter in the camera. Picture light entering camera as water flowing through a pipe. Beam splitter would be like dividing an identical amt of water into three diff pipes. Each sensor gets an identical look at the image. Each sensor only responds to one of the primary colors due to the filters.
2. This method is known as spinning disk. Basically, it is to rotate a series of red, blue and green filtersin front of a sensor.

A spinning disk filter

3. Interpolation is to permanently place a filter over each individual photosite. This is the process of looking at the other pixels in the neighborhood of a sensor and making an educated guess.

4. Bayer filter pattern alternates a row of red and green filters with a row of blue and green filters.Only one sensor is required, and all the color information (red, green and blue) is recorded at the same moment. That means the camera can be smaller, cheaper, and useful in a wider variety of situations.

5. "Digital cameras use specialized demosaicing algorithms to convert the mosaic of separate colors into an equally sized mosaic of true colors. The key is that each colored pixel can be used more than once. The true color of a single pixel can be determined by averaging the values from the closest surrounding pixels. "