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Digital Picture Basics Lesson 1 - How Does A Digital Camera Work?

Digital cameras have really caught on with the general public since electronic pictures can be loaded onto a computer, which eliminates the need for expensive photo development equipment. Pictures can also be easily shared through the help of the internet, especially now with social networking sites being so popular.

Since film still provides better picture quality, digital cameras have not completely replaced conventional cameras. But, as digital imaging technology has improved, digital cameras have rapidly become more popular.

The digital camera truly different from its a conventional camera which depends entirely on chemical and mechanical processes. In fact, you don't even need electricity to operate conventional cameras. To truly appreciate how digital cameras have made our lives easier, we will have a look at how conventional film cameras work.

Conventional Film Cameras

A conventional camera would use a roll of film (a very light-sensitive material) that would rotate a a single film frame across a shutter for each picture. When you pushed the button to take the photo, the shutter would open and the light that came in would burn an image into the film frame.

Traditional film camera body
Light-sensitive film material is separated into frames


The film is stored in a roll to protect it from light
Inside the camera body, the film is rolled one frame at a time across the closed shutter.
When the shutter opens the light coming through the lens burns an image of whatever the lens sees onto the exposed film frame

After this, the film roll would be taken into a "Dark Room" to be processed into prints using special chemicals.

A Dark Room With Film Processing Equipment

Seems like a lot of work, doesn't it? Now let's look at how digital cameras have changed the way we take and view photos.

Digital Camera Basics

So how do these things work? 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.

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, process the film chemically, print it onto photographic paper and then use a digital scanner to scan 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 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.

CCD and CMOS: Filmless Cameras

Instead of film, a digital camera has a sensor that converts light into electrical charges.

There are two devices that can be used for this. The first and most popular choice among camera manufacturers is the charge coupled device (CCD). Some cameras use complementary metal oxide semiconductor (CMOS) technology instead.

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A simplified way to think about these sensors is to think of a grid of millions boxes.

Close Up Image of A CCD

Think of the CCD as being a grid of millions of little squares. Each of those little squares on the CCD takes light energy and converts it to electrical energy. Each condition of the light – like brightness and intensity – generates a very specific electrical charge. Those charges for each little square are then transported processing chip which can interpret the electrical charges. The tranlation includes information such as colour and other qualities of the light that the CCD picked up.

In short, every box on the CCD grid senses light energy and then the processor assigns that grid box a value for each RGB colour (Red Green and Blue). The image that is stored is now simply a grid of boxes, each with their own piece of colour information (recorded in 0s and 1s).

efThis grid is what gives your computer the ability to re-create the colours and definition of a photo.

Below you will see a digital photo that has been magnified so that you can see that it is nothing more than a collection of individual dots (pixels).




Image that is 400 pixels wide by 300 pixels high.



A magnified view of the dog's eye. You can see that the whole image above is made up of tiny boxes (pixels) that contain only one piece of information (the RGB value).



Advantages to Digital Cameras

• Instant review of pictures, with no wait for the film to be developed: if there's a problem with a picture, the photographer can immediately correct the problem and take another picture

• Minimal ongoing costs for those wishing to capture hundreds of photographs for digital uses, such as computer storage and e-mailing, but not printing

• If one already owns a newer computer, permanent storage on digital media is considerably cheaper than film.

• Photos may be copied from one digital medium to another without any degradation

• Pictures do not need to be scanned before viewing them on a computer

• Ability to print photos using a computer and consumer-grade printer

• Ability to embed metadata within the image file, such as the time and date of the photograph, model of the camera, shutter speed, flash use, and other similar items, to aid in the reviewing and sorting of photographs. Film cameras have limited ability to handle metadata, though many film cameras can "imprint" a date over a picture by exposing the film to an internal LED array (or other device) that displays the date.

• Ability to capture and store hundreds of photographs on the same media device within the digital camera; by contrast, a film camera would require regular changing of film (typically after every 24 or 36 shots)

• Many digital cameras now include an AV-out connector (and cable) to allow the reviewing of photographs to an audience using a television

• Anti-shake functionality (increasingly common in inexpensive cameras) allow taking sharper hand-held pictures where previously a tripod was required

• Ability to change ISO speed settings more conveniently in the middle of shooting, for example when the weather changes from bright sunlight to cloudy. In film photography, film must be unloaded and new film with desired ISO speed loaded.

• Ability to use the same device to capture video as well as still images.

• Ability to convert the same photo from color to sepia to black & white