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