Bits & Bytes (are not junk food!)

Bit is short for binary digit, the smallest unit of information in the digital world. A single bit can hold only one of two values: 0 or 1. (On or Off) A bit-mapped image is made up of dots. A dot is a single point, the smallest identifiable part of an image. Image files are often described by the number of bits used to represent each dot or pixel.

Bit depth -- also called pixel depth or color depth -- measures how much color information is available to display or print each pixel in an image. Greater bit depth (more bits of information per pixel) means more available colors and more accurate color representation in the digital image.

A 1-bit image is monochrome, each dot is either on or off; hence the image is only rendered in black and white, with no shades of gray. An 8-bit image supports 256 grayscales or 256 colors.

256?????

2x2x2x2x2x2x2x2 = 256 or 2 to the power of 8 256?????

2x2x2x2x2x2x2x2 = 256 or 2 to the power of 8 We often call an RGB image 8- bit. Actually it is 8-bits per color channel (8x3). 256?????

This is also referred to as a 24-bit image. Each dot or pixel is represented by 24 bits. Using 24 bits means that more than 16 million unique colors can be represented. Since humans can only distinguish a few million colors, this is more than enough to accurately represent a color image.

A 16-bit per channel image actually has 48 bits (16x3) of color information in each pixel. A 48 bit image is capable of billions of colors. This is available with RAW files and high end cameras.

RESOLUTION or REZ for short

A camera that captures 1600 x 1200 pixels produces an image with a resolution of 1.92 million pixels and would be referred to as a 2.0 megapixel camera. You get to 1.92 million pixels by multiplying the vertical and horizontal dimensions. That number is then rounded off to 2 for marketing purposes.

There is true resolution and interpolation. Interpolation is the process of "sizing up" a digital image by adding pixels that were not there originally. Since every pixel must have a color, this process usually involves assigning an intermediate color to the "invented" pixels based upon the colors of the pre-existing pixels surrounding the new ones.

The result is a larger image in terms of resolution, but one that now has less clarity because you simply cannot produce something from nothing.

Need more info? On-line resources: Textbook pages

Exposure When light is allowed to pass through the lens, and through the opened shutter curtain in the camera, you have exposed light to the film (CCD, CMOS, or Foveon sensor with digital). The amount of light you allow to reach the film or sensor is a result of two basic functions, aperture and shutter speed; both play a part in creating an exposure.

Aperture: The size of the opening in a lens through which light passes is controlled by the aperture setting. It controls the volume of light transmitted to your film or sensor, in terms of stops such as f/2.8, f/4, f/5.6, f/8 and so forth.

Shutter Speed: The duration of time that the shutter curtain is open in your camera, allowing light to hit the film or sensor is controlled by shutter speed. This is reflected in the fractional term such as 1/30th of a second, 1/60th, 1/125th, 1/250th and so forth. 4. Correct Exposure: The proper combination of aperture and shutter speed to get the results you desire is correct exposure. 5. Bracketing: The over- or under-exposing of the camera's metered choice for correct exposure. How much or how far you bracket is up to you, i.e., 1/3, 1/2, or 1 full stop, for example.

So…. Aperture controls how much. Shutter speed controls how long. The proper combination of aperture and shutter speed to get the results you desire is correct exposure.

Bracketing: The over- or under-exposing of the camera's metered choice for correct exposure. How much or how far you bracket is up to you, i.e., 1/3, 1/2, or 1 full stop, for example.

With a film camera you change the type of film in order to match the type of light you're photographing in. With a digital camera you adjust the white balance to match the light that you're shooting in.