20 Sep 08 Digital Camera Basics-images
Author: Brian Lee
In the past twenty years, most of the major technological breakthroughs in consumer electronics have been built around the same basic process: converting conventional analog information (represented by a fluctuating wave) into digital information (binary information represented by ones and zeros, or bits). This fundamental shift in technology has changed how we handle visual and audio information — it completely redefined what is possible.
The digital camera is one of the most notable examples of this shift because it is so truly different from its predecessor. Conventional film cameras depend entirely on chemical and mechanical processes — you don’t need any electricity whatsoever to operate them, other than for a flash. On the other hand, all digital cameras have a built-in computer, and all of them record images electronically.
The new approach has been enormously successful. Since film usually provides better picture quality, digital cameras have not completely replaced conventional cameras. But, as digital imaging technology has improved, and prices dramatically decreased, digital cameras have rapidly become more popular.
In this article, we’ll find out exactly what’s going on inside these amazing digital-age devices.
Understanding the Basics
Let’s say you want to take a picture and e-mail it to a friend. To do this, you need the image to be represented in the language that computers recognize — bits and bytes, or binary information. Essentially, a digital image is just a long string of 1s and 0s that represent all the tiny colored dots — or pixels — that collectively make up the image. If you want to get a picture into this form, you have two options:
1) You can take a photograph using a conventional film camera, take the film to a developing lab that processes the film chemically, prints it onto photographic paper, and then place the picture on a digital scanner to sample the print (record the pattern of light as a series of pixel values).
2) You can directly sample the original light that bounces off your subject, immediately breaking that light pattern down into a series of pixel values — in other words, you can use a digital camera.
At its most basic level, this is all there is to a digital camera. Just like a conventional film camera, it has a series of lenses that focus light to create an image of a scene. But instead of focusing this light onto a piece of film, it focuses it onto a semiconductor device that records light electronically. A computer then breaks this electronic information down into digital data. All the fun and interesting features of digital cameras come as a direct result of this process.
Instead of film, a digital camera has a sensor that converts light into electrical charges.
The image sensor employed by most digital cameras is a charge coupled device (CCD). Some cameras use complementary metal oxide semiconductor (CMOS) technology instead. Both CCD and CMOS image sensors convert light into electrons. Without getting too technical, a simplified way to think about these sensors is to think of a 2-dimentional array of thousands or millions of tiny solar cells.
Once the sensor converts the light into electrons, it reads the value (accumulated charge) of each cell in the image. This is where the differences between the two main sensor types become a factor:
A CCD transports the charge across the chip and reads it at one corner of the array. An analog-to-digital converter (ADC) then turns each pixel’s value into a digital value by measuring the amount of charge at each photosite and converting that measurement to binary form. CCD sensors create high-quality, low-noise images. 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 devices use several transistors at each pixel to amplify and move the charge using ordinary wires. The CMOS signal is digital, so it needs no ADC. Because each pixel on a CMOS sensor has several transistors located next to it, the light sensitivity of a CMOS chip is lower (many of the photons hit the transistors instead of the photodiode.) CMOS sensors traditionally consume little power. CCDs, on the other hand, use a process that consumes lots of power.
The amount of detail that the camera can capture is called the resolution, and it is measured in pixels. The more pixels a camera has, the more detail it can capture and the larger pictures can be without becoming blurry or “grainy.” High-end consumer cameras can capture over 12 million pixels. Some professional cameras support over 16 million pixels, or 20 million pixels for large-format cameras. For comparison, Hewlett Packard estimates that the quality of 35mm film is about 20 million pixels.
Exposure and Focus
Just as with film, a digital camera has to control the amount of light that reaches the sensor. The two components it uses to do this, the aperture and shutter speed, are also present on conventional cameras.
Aperture: The size of the opening in the camera. The aperture is automatic in most digital cameras, but some allow manual adjustment to give professionals and hobbyists more control over the final image.
Shutter speed: The amount of time that light can pass through the aperture. Unlike film, the light sensor in a digital camera can be reset electronically, so digital cameras have a digital shutter rather than a mechanical shutter.
These two aspects work together to capture the amount of light needed to make a good image. In photographic terms, they set the exposure of the sensor.
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19 Sep 08 How Do I Choose a Digital Camera?
Author: J Adams
A digital camera might look like a film camera but they are actually quite different. Both freeze light to make a photograph. Film cameras do this chemically using film. Digital cameras use a light sensitive CCD or CMOS silicon chip to convert light and digital information into pixels.
Pixels are the tiniest areas of light that your digital camera can recognize and change into information. The greater amount of pixels the more detail and higher the resolution the photograph. A low resolution color printout of tree will show that it is green but in a high resolution photograph the leaves and texture of the bark will be more sharply defined.
With digital photographs your have the ability to use software like Adobe Photoshop Deluxe and Microsoft Picture to edit photos and make corrections.
Choosing Your Camera
Important considerations when choosing a digital camera are: What do you want the camera to do? What features do you require? How much do you wish to spend on your camera?
There are professional high end cameras that cost thousands of dollars, cheap throwaway cameras and a huge selection of mid-level cameras available to choose from.
Will you be photographing images for the internet and for email? Will your photos be printed? For regular print size snapshots and web photos a one to two megapixel camera will do. In fact for the web a lower megapixel would be better as higher resolution photos are slow to download.
Do you want a point-and-click camera? Are you someone who just wants to get the picture taken with the least amount of bother. Do you want a camera that does everything automatically and you simply have to press a button? Or, are you someone who would rather figure out the best settings for your camera and make the adjustments manually? It’s always best to find a camera that suits your purpose, need and ability.
High or Low Resolution
High end, high resolution cameras are good for photographs that are to be printed. The greater the number of pixels the higher the resolution. High resolution does not make sense on the web as the extra resolution does not make images appear any sharper. Also, high resolution photos are slow to download on the web.
To print your photographs you will need a good quality color printer. If photos are to be printed, high resolution does make a difference depending how large you want the picture to be. High resolution will give a large print better definition. High resolution cameras cost more. Expect to pay more for high resolution. You also need to check that your printer can handle high resolution prints.
Lenses
Low-end digital cameras have fixed focus lenses made of plastic. With these lenses everything is focused and you don’t need to make a decision what to focus on.
Variable focused lenses are made of glass or high quality plastic. These lenses focus on whatever object you are trying to capture in a photograph.
Most mid-range digital cameras come with auto focus and manual focus built in. Auto focus is for point-and-click photos of whatever is in the middle of the frame. Or, by turning the ring over the lens, you can manually focus the camera. These cameras allow users to switch between auto and manual focus.
Zoom Lenses
Digital cameras have optical zoom and digital zoom lenses. Optical zoom costs more, give a better quality picture, and works the same way as on non-digital cameras with lens adjustments. A digital zoom comes about when the camera makes calculations to manipulates the pixels. Digital zoom gives a less sharp image. Some cameras include both optical and digital zoom.
View Finder
The view finder is what you look through to see what you are photographing. The view finder on both digital and regular film cameras will approximate the picture your lens is viewing. Digital cameras will also come with an LCD display that you can use to check your photographs and decide weather or not to keep them.
Lighting
When it comes to lighting you might not want the camera to make the decision automatically for you. On an auto setting you camera might not make the best lighting choice given the location and environment. At times like this you can appreciate being able to switch between manual and automatic settings.
Digital cameras allow you to test exposure and view a picture on LCD prior to pressing the button fully and committing to a photograph.
Flash
There will be a built in flash that comes with your digital camera. In addition, the better cameras have a location for a flash attachment. This is a good option for producing better quality photographs.
Connecting to Your Computer
You will need a PC USB cable, or for Mac’s - Firewire or Mac USB cable, to connect to your computer. You will also need a cable adapter for your camera’s CF (Compact Flash) or SM (Smart Media) card .
The CF or SM cards are removable high capacity storage cards for your photos. Your camera will use one type of card or the other. Not both. Check to see which type of storage card your camera uses.
USB connections are fast and easy to set up. Older cameras connect through a serial port. USB is faster and does not require that the computer be rebooted before it recognizes the camera.
Batteries and AC Adapters
Digital cameras often come with rechargeable batteries. It is best to have two sets of batteries. One set to use while the other is recharging. AC adapters make it easy to plug into an electrical outlet when you are near by one.
Main Drawback of Digital Camera
The main drawback of digital cameras is shutter lag delays when the camera delays responding after you squeeze the button. It is possible you may miss the moment when photographing moving objects due to shutter lag. Some of the newer cameras are beginning to address the problem.
Select a camera that does what you want it to do, has features you will use and is priced in the range you want to pay. This will be the right camera for you. If your experience is limited and you do not want to take a lot of time learning how to use the camera, go with a point-and-shoot camera. Something without too many features. If you are a camera enthusiast who wants to do more with your camera or is willing to take the time to learn how to use the feature then, by all means go all out.
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