Digital PhotographyBasics

Pixels A pixel is a contraction if the term PIcture ELement. Digital

images are made up of small squares, just like a tile mosaic on your kitchen or bathroom wall. Though a digital photograph looks smooth and continuous just like a regular photograph, it's actually composed of millions of tiny squares as shown below.

Pixels Each pixel in the image has a numerical value of between 0

and 255 and is made up of three color channels. So for example a pixel could be 37-red, 76-green and 125-blue.

So for example a pixel could be 37-red, 76-green and 125-blue and it would then look like this

Aspect Ratio The aspect ratio of a camera is the ratio of the length of the

sides of the images. For example, a traditional 35mm film frame is approximately 36mm wide and 24mm HIGH. This has an aspect ratio of 36:24, which can equally well be expressed as 3:2. Some digicams use the same aspect ratio for their digital images. For example most digital SLR (single lens reflex) cameras have a 3:2 aspect ratio. However, video monitors typically use a 4:3 aspect ratio. For example a monitor with a 800x600 display has a 4:3 aspect ratio. With this in mind, most consumer level digicams use a 4:3 aspect ratio for their images.

Digital Zoom and Optical Zoom Most cameras have both optical zoom and digital zoom. Optical zoom

works just like a zoom lens on a film camera. The lens changes focal length and magnification as it is zoomed. Image quality stays high throughout the zoom range. Digital zoom simply crops the image to a smaller size, then enlarges the cropped portion to fill the frame again. Digital zoom results in a significant loss of quality as is clear from the examples below. It's pretty much a last resort, and if you don't have it in camera, you can do a similar job using almost any image editing program

Sensitivity

Sensitivity settings on digital cameras are the equivalent of ISO ratings on film. Just about every digital camera will have settings with a sensitivity equivalent to ISO 100 film and ISO 200 film. Many will have an ISO 400 setting, but above that the images from cameras with small sensors gets pretty noisy. The more expensive digital SLRs with much larger sensors have much higher sensitivity settings. At ISO 400 they are virtually noise free and some can go as high as ISO 3200 or even ISO 6400! Very few cameras have ISO setting lower than ISO 100 because noise levels are so low at ISO 100 there would be no real advantage in a slower setting. Quite a few digital cameras have an "auto" ISO setting, where the camera will pick from ISO 100, ISO 200 and sometimes ISO 400, depending on the light level and the mode in which the camera is operating.

What is ISO

What ISO denotes is how sensitive the image sensor is to the amount of light present. The higher the ISO, the more sensitive the image sensor and therefore the possibility to take pictures in low-light situations.

What Is... Correct Exposure?

A correctly exposed image means that the right amount of light has exposed the image sensor. There are basically two ways your camera can ensure that:

1) open or close the aperture (by making the hole of the iris larger or smaller; or, as is becoming more and more common in point-and-shoot digicams, by using a neutral density filter to restrict the amount of light reaching the image sensor);

2) 2) by deciding how long to leave the shutter open.

3) A third way that we will also briefly look at is by adjusting the ISO (basically boosting the light signal).

Aperture and Shutter Speed When you (or your camera) uses a larger aperture (e.g.

F2.8), the hole of the iris is larger and more light reaches the image sensor.

Conversely, using a smaller aperture (e.g. F8) means that the hole of the iris is smaller and less light reaches the image sensor

Shifting Aperture and Shutter Speed When a fast shutter speed is used (e.g. 1/1,000 sec.),

the image sensor is exposed for only that small amount of time (i.e. 1/1,000 sec.). Conversely, when a slow shutter speed is used (e.g. 1/30 sec.; some cameras allow slow shutter speeds up to 30 sec. or more), the image sensor is exposed for that longer amount of time.

F8 1/30

Info Links

Effects of sensor size on image quality Choosing a Digital Camera Digital and Depth of Field