| In the past twenty years, most of the major | | | | Some cameras use complementary metal oxide |
| technological breakthroughs in consumer | | | | semiconductor (CMOS) technology instead. Both |
| electronics have really been part of one | | | | CCD and CMOS image sensors convert light into |
| larger breakthrough. When you get down to it, | | | | electrons. If you've read How Solar Cells |
| CDs, DVDs, HDTV, MP3s and DVRs are all built | | | | Work, you already understand one of the |
| around the same basic process: converting | | | | pieces of technology used to perform the |
| conventional analog information (represented | | | | conversion. A simplified way to think about |
| by a fluctuating wave) into digital | | | | these sensors is to think of a 2-D array of |
| information (represented by ones and zeros, | | | | thousands or millions of tiny solar cells. |
| or bits). This fundamental shift in | | | | |
| technology totally changed how we handle | | | | Once the sensor converts the light into |
| visual and audio information -- it completely | | | | electrons, it reads the value (accumulated |
| redefined what is possible. | | | | charge) of each cell in the image. This is |
| | | | where the differences between the two main |
| The digital camera is one of the most | | | | sensor types kick in: |
| remarkable instances of this shift because it | | | | |
| is so truly different from its predecessor. | | | | A CCD transports the charge across the chip |
| Conventional cameras depend entirely on | | | | and reads it at one corner of the array. An |
| chemical and mechanical processes -- you | | | | analog-to-digital converter (ADC) then turns |
| don't even need electricity to operate them. | | | | each pixel's value into a digital value by |
| On the other hand, all digital cameras have a | | | | measuring the amount of charge at each |
| built-in computer, and all of them record | | | | photosite and converting that measurement to |
| images electronically. | | | | binary form. |
| | | | |
| The new approach has been enormously | | | | CMOS devices use several transistors at each |
| successful. Since film still provides better | | | | pixel to amplify and move the charge using |
| picture quality, digital cameras have not | | | | more traditional wires. The CMOS signal is |
| completely replaced conventional cameras. | | | | digital, so it needs no ADC. |
| But, as digital imaging technology has | | | | |
| improved, digital cameras have rapidly become | | | | Differences between the two types of sensors |
| more popular. | | | | lead to a number of pros and cons: |
| | | | |
| In this article, we'll find out exactly | | | | CCD sensors create high-quality, low-noise |
| what's going on inside these amazing | | | | images. CMOS sensors are generally more |
| digital-age devices. | | | | susceptible to noise. |
| | | | |
| Understanding the Basics | | | | Because each pixel on a CMOS sensor has |
| | | | several transistors located next to it, the |
| Let's say you want to take a picture and | | | | light sensitivity of a CMOS chip is lower. |
| e-mail it to a friend. To do this, you need | | | | Many of the photons hit the transistors |
| the image to be represented in the language | | | | instead of the photodiode. |
| that computers recognize -- bits and bytes. | | | | |
| Essentially, a digital image is just a long | | | | CMOS sensors traditionally consume little |
| string of 1s and 0s that represent all the | | | | power. CCDs, on the other hand, use a process |
| tiny colored dots -- or pixels -- that | | | | that consumes lots of power. CCDs consume as |
| collectively make up the image. (For | | | | much as 100 times more power than an |
| information on sampling and digital | | | | equivalent CMOS sensor. |
| representations of data, see this explanation | | | | |
| of the digitization of sound waves. | | | | CCD sensors have been mass produced for a |
| Digitizing light waves works in a similar | | | | longer period of time, so they are more |
| way.) | | | | mature. They tend to have higher quality |
| | | | pixels, and more of them. |
| If you want to get a picture into this form, | | | | |
| you have two options: | | | | Although numerous differences exist between |
| | | | the two sensors, they both play the same role |
| You can take a photograph using a | | | | in the camera -- they turn light into |
| conventional film camera, process the film | | | | electricity. For the purpose of understanding |
| chemically, print it onto photographic paper | | | | how a digital camera works, you can think of |
| and then use a digital scanner to sample the | | | | them as nearly identical devices. |
| print (record the pattern of light as a | | | | |
| series of pixel values). | | | | Resolution |
| | | | |
| You can directly sample the original light | | | | The amount of detail that the camera can |
| that bounces off your subject, immediately | | | | capture is called the resolution, and it is |
| breaking that light pattern down into a | | | | measured in pixels. The more pixels a camera |
| series of pixel values -- in other words, you | | | | has, the more detail it can capture and the |
| can use a digital camera. | | | | larger pictures can be without becoming |
| | | | blurry or "grainy." |
| At its most basic level, this is all there is | | | | |
| to a digital camera. Just like a conventional | | | | Some typical resolutions include: |
| camera, it has a series of lenses that focus | | | | |
| light to create an image of a scene. But | | | | 256x256 - Found on very cheap cameras, this |
| instead of focusing this light onto a piece | | | | resolution is so low that the picture quality |
| of film, it focuses it onto a semiconductor | | | | is almost always unacceptable. This is 65,000 |
| device that records light electronically. A | | | | total pixels. |
| computer then breaks this electronic | | | | |
| information down into digital data. All the | | | | 640x480 - This is the low end on most "real" |
| fun and interesting features of digital | | | | cameras. This resolution is ideal for |
| cameras come as a direct result of this | | | | e-mailing pictures or posting pictures on a |
| process. | | | | Web site. |
| | | | |
| In the next few sections, we'll find out | | | | 1216x912 - This is a "megapixel" image size |
| exactly how the camera does all this. | | | | -- 1,109,000 total pixels -- good for |
| | | | printing pictures. |
| Cool Facts | | | | |
| | | | 1600x1200 - With almost 2 million total |
| With a 3-megapixel camera, you can take a | | | | pixels, this is "high resolution." You can |
| higher-resolution picture than most computer | | | | print a 4x5 inch print taken at this |
| monitors can display. | | | | resolution with the same quality that you |
| | | | would get from a photo lab. |
| You can use your Web browser to view digital | | | | |
| pictures taken using the JPEG format. | | | | 2240x1680 - Found on 4 megapixel cameras -- |
| | | | the current standard -- this allows even |
| The first consumer-oriented digital cameras | | | | larger printed photos, with good quality for |
| were sold by Kodak and Apple in 1994. | | | | prints up to 16x20 inches. |
| | | | |
| In 1998, Sony inadvertently sold more than | | | | 4064x2704 - A top-of-the-line digital camera |
| 700,000 camcorders with a limited ability to | | | | with 11.1 megapixels takes pictures at this |
| see through clothes. | | | | resolution. At this setting, you can create |
| | | | 13.5x9 inch prints with no loss of picture |
| A Filmless Camera | | | | quality. |
| | | | |
| A CMOS image sensor | | | | High-end consumer cameras can capture over 12 |
| | | | million pixels. Some professional cameras |
| Instead of film, a digital camera has a | | | | support over 16 million pixels, or 20 million |
| sensor that converts light into electrical | | | | pixels for large-format cameras. For |
| charges. | | | | comparison, Hewlett Packard estimates that |
| | | | the quality of 35mm film is about 20 million |
| The image sensor employed by most digital | | | | pixels . |
| cameras is a charge coupled device (CCD). | | | | |