Aspect ratio

The ratio of width to height.  A standard 35mm film frame is 36 x 24mm so the aspect ratio is 3:2.   A 4x5”  camera has an aspect ration of 5:4.  2¼ square cameras have an aspect ration of 1:1.

Bit depth

Bit depth is the number of computer bits used for color and tonal information.  This can be expressed per channel (8 bits for example) or as a total for all channels. RGB can have 8 bits/channel so can be referred to as 24-bit color.  It can also have 16 bits/channel for a total of 48 bits.  Note that a higher bit depth does not mean more information, but rather the same information in finer increments.

Black point

The tone at which a printer no longer distinguishes any other darker tone.  White point is the exact opposite.  Remember that the whitest point in a print is the paper itself.

Brightness

The amount of light being reflected off a subject.

Capture

To record an image with a digital device, either by taking a picture with a digital camera or by scanning.

Clipping

When an image has been either over or under exposed to the point that there is loss of detail in the highlights or shadows.

CMYK

Cyan, magenta, yellow, and black (black is sometimes referred to as “key”).  The colors of a “four color printing press.”

File format

Describes how information is arranged and stored in a file.  Some standard imaging file formats are JPEG, TIFF, PSD (Photoshop Document).  RAW is not a file format but rather a description of the data captured by a device.  Each camera company has a RAW file format such as Nikon’s NEF (Nikon Electronic Format).

Full frame

An argumentative term used in web forums.  By definition all cameras are full frame.  Full frame standard 35mm film cameras have a frame size of 24x36mm.  Full frame 4x5” cameras have a frame size of 4x5 inches.  If you’re not getting “full frame” then either the shutter is not opening all the way or the recording media was not properly inserted.  There is no such thing as a “non-full-frame” digital camera.  Some web forum users insist that only a 35mm film camera is full frame.  If that is true does it follow that medium format is then “big frame” while 4x5 is “super frame” and 8x10 “super-deluxe-biggie-humongous”?

Gamut

The colors included out of all possible colors.

Histogram

A graph plotting the distribution of a image’s tones against the digital tonal scale from tone 0 (black) on the left to tone 255 (white) on the right.

Hue

One of three basic descriptions of a color: hue, saturation, and lightness.  Hue is what we generally think of as the “color” of something, such as “green” or “red.”  Saturation is how pure the hue is, while lightness is how light or dark it is.

Luminance

A measurement of an object’s brightness.

Out of gamut

A color that cannot be reproduced by the current device.

Pixel

A picture element.

Posterization

The visible banding in an image caused by not having a smooth gradation between tones.

PPI

Pixels per inch.  Not to be confused with DPI (dots per inch), although often used interchangeably.  Digital files are measured in ppi, while prints are measured in dpi.  A Nikon scanner yields 4000 ppi.  Files for printing are commonly in the 240-300 ppi range while the printer could be set for 1440 dpi.  File size remains the same when the PPI alone is changed; a 10 x 10” image at 100 ppi has the exact same number of pixels as a 20 x 20” image file at 50 ppi.

RGB

Red, Green, Blue.  Notice that these are letter-for-letter the complimentary colors (the exact opposites on the color wheel) of CMY.
 

Saturation

How pure a hue is.  100% saturated hues are very vivid.  When all saturation is removed what is left is monochrome, i.e., black and white.

Stop

A doubling or halving of an amount of light.  Two 100 watt light bulbs are one stop more light than one 100 watt light bulb.

Tonal range

A tonal scale.  In the digital world this runs from value 0 (black) to 255 (white) for a total of 256 steps.

Tone

A measurement of an object’s lightness.