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1. Introduction ……………………………………..3 12. Irrelavancy…………………………………….25

2. The Basics ………………………………………. 4 13. Interface………………………………………..26

3. How it works ………………………………….. 5 14. Image Stabilization……………………..27

4. Image Sensors………………………………… 7 15. Focus……………………………………………….27

5. How the camera captures colour .. 11 16. Macro…………………………………………… .28

6. Some technical details……………….... 16 17. Batteries…………………….………………… 29

7. FAQ’s …………………………………………..…...18 18. Flash………………………………………………..30

8. Output…………………………………………….... 21 19. Software………………………………………...31

9. Storage ………………………………………..…..22 20. Bibliography…………………………………...32

10. Compression …………………………………. 23 21. The End……………………………………………33

11. Repitition………………………………………...24

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Megapixel digital cameras are coming down in price, while the quality and number of features of these cameras keeps going up. Some projections suggest that digital cameras will become as popular as film-based cameras by 2005. A digital camera converts light into an image that can be stored on a computer or printed out on a desktop printer.

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The Basics

If you want to take a picture of your dog and e-mail it to a friend. The first step is to create a digital version of the image, so your computer can process it. You do that by:Using a digital scanner to sample your photograph. Use a device that will sample the original light that bounces off your dog to create a digital image. This device is called a digital camera. Sometimes, it is referred to as a filmless camera.

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The difference between a digital camera and a film-based camera is that the digital camera has no film. Instead, it has a sensor that converts light into electrical charges.

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•charge coupled device (CCD) :Most cameras.

•complementary metal oxide semiconductor (CMOS) technology: Some low-end cameras

Image sensors:

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Differences between CMOS and CCDCCD CMOS

•More expensive•Charge transported across the chip and read at one corner of the array.

•An analog-to-digital converter turns each pixel's value into a digital value

•High-quality, low-noise images

•Less expensive to manufacture•Several transistors at each pixel which amplify and move the charge using more traditional wires.

• The CMOS approach is more flexible because each pixel can be read individually.

•More susceptible to noise

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The CCD is a collection of tiny light-sensitive diodes, which convert photons (light) into electrons (electrical charge). These diodes are called photosites. In a nutshell, each photosite is sensitive to light -- the brighter the light that hits a single photosite, the greater the electrical charge that will accumulate at that site.

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A CMOS image sensor

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How the Camera Captures Color

Unfortunately, each photosite is colorblind. It only keeps track of the total intensity of the light that strikes its surface. In order to get a full color image, most sensors use filtering to look at the light in its three primary colors. Once all three colors have been recorded, they can be added together to create the full spectrum of colors that you've grown accustomed to seeing on computer monitors and color printers.

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Light is directed to the different sensors by placing a beam splitter in the camera. A beam splitter would be like dividing an identical amount of water into three different pipes. Each sensor gets an identical look at the image, but because of the filters, they only respond to one of the primary colors.

The highest quality cameras use three separate sensors, each with a different filter over it.

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In order to digitize the information, the signal must be passed through an analog-to-digital converter (ADC). Interpolation is handled by a microprocessor after the data has been digitized.

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Think of each photosite as a bucket or a well. Now think of the photons of light as raindrops. As the raindrops fall into the bucket, water accumulates (in reality, electrical charge accumulates). Some buckets have more water and some buckets have less water, representing brighter and darker sections of the image. Keeping to the analogy, the ADC measures the depth of the water, which is considered analog information. Then it converts that information to binary form.

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Is the Number of Photosites the Same as the Number of Pixels?The number of pixels and the max resolution numbers don't quite compute. For example, a camera claims to be a 2.1 mega-pixel camera and it is capable of producing images with a resolution of 1600 X 1200. A 1600 x 1200 image contains 1,920,000 pixels. But 2.1 mega-pixel means there ought to be at least 2,100,000 pixels. This isn't an error from rounding off, and it isn't binary mathematical trickery. There is a real discrepancy between these two numbers. If a camera says it has 2.1 mega-pixels, then there really are approximately 2,100,000 photosites on the CCD.

What happens is that some of the photosites are not being used for imaging. The CCD is an analog device. It's necessary to provide some circuitry to the photosites so that the ADC can measure the amount of charge. This circuitry is dyed black so that it doesn't absorb any light and distort the image.

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How Big Are the Sensors?

The current generation of digital sensors are smaller than film. Typical film emulsions that are exposed in a film-based camera measure 24 mm X 36 mm. If you've look at the specifications of a typical 1. 3 mega-pixel camera, you'll find that it has a CCD sensor that measures 4.4 mm X 6.6 mm. A smaller sensor means smaller lenses.

You should keep track of the current literature, because things change fast in this field. At the time of this writing, there is a CCD sensor that contains over 6 million photosites and is approximately the size of standard 35 mm film.

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Most digital cameras on the market today have an LCD screen, which means that you can view your picture right away. This is one of the great advantages of a digital camera: You get immediate feedback on what you capture. Once the image leaves the CCD sensor (by way of the ADC and a microprocessor), it is ready to be viewed on the LCD.

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To get the pictures out, they need to be hooked up directly to a computer by cables so that the images could be transferred. Although most of today's cameras are capable of the connecting to a serial, parallel, SCSI, and/or USB ports, they usually provide you with some sort of removable storage device. The main rival technologies are CompactFlash, SmartMedia and Memory Sticks, but there are others. These three are all small, removable, solid-state flash memory devices that have no moving parts. They are fast, inexpensive ways of storing your photos so that you can transfer them to a computer or printer later on.

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It takes a lot of memory to store a picture with over 1.2 million pixels. Almost all digital cameras use some sort of data compression to make the files smaller. There are two features of digital images that make compression possible:

• repetition.

•irrelevancy.

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RepititionYou can imagine that throughout a given photo, certain patterns develop in the colors. For example, if a blue sky takes up 30 percent of the photograph, you can be certain that some shades of blue are going to be repeated over and over again. When compression routines take advantage of patterns that repeat, there is no loss of information and the image can be reconstructed exactly as it was recorded in the camera. Unfortunately, this doesn't reduce files any more than 50 percent, and sometimes it doesn't even come close to that level.

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IrrelevancyIrrelevancy is a trickier issue. A digital camera

records more information than is easily detected by the human eye. Some compression routines take advantage of this fact to throw away some of the more meaningless data. If you need smaller files, you need to be willing to throw away more data. Most cameras offer several different levels of compression, although they may not call it that. More likely they will offer you different levels of resolution. This is the same thing. Lower resolution means more compression. And more compression means lower resolution.

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The interface allows you to connect the camera to your computer and transfer the images. There are different ways to move images from the camera to the computer:

•USB connection - fast, easy way to download images. Need USB port.

•Serial connection - slow way to download images, but works on almost any computer.

•Floppy disk - If your camera uses a floppy disk (or writeable CD/DVD), then simply pop the floppy disk into any computer.

•Flash memory slots - It is possible to add a box to your computer that will let you remove a Compact Flash card from the camera and attach it directly to the computer.

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Image StabilizationSome cameras offer a "steady cam" image stabilization system like video cameras have. A system like this can help you take clearer images

FocusMost cameras have fixed focus, so you can not adjust the focus at all, or automatic focus. If you would like more control, choose a camera with a manual focus feature.

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Digital cameras, especially those that use a CCD sensor and an LCD display, tend to use lots of power -- which means they eat batteries. Rechargeable batteries help to lower the cost of using the digital camera, but rechargeable batteries are sometimes expensive.

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Most cameras come with a built-in flash. Normal modes are:

Automatic Forced flash Fill flash No flash

You definitely want to be able to turn off the flash -- some completely automatic cameras do not allow this.

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Most cameras come with some sort of software. You use the software to download images from the camera and manipulate them on the computer. Unless you already have software that you are comfortable with, you want to make sure that your camera comes with something.

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1.Http://www.howstuffworks.com

2.Http://www.digitalcamera.com

3.Http://www.olympus.com

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