Christopher John Ball Fine Arts Photographer and Writer
Glossary of Digital Photography Terms
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Bitmap image
An image with 1 bit of colour information per pixel, also known as a bitmapped image. The only colours displayed in a bitmapped image are black and white.

Brightness
One of three dimensions of colour; the other two are hue and saturation. The term is used to describe differences in the intensity of light reflected from or transmitted through an image independent of its hue and saturation

CMYK
The four process colours used in printing: cyan, magenta, yellow, and black.

CMYK image
A four-channel image containing a cyan, magenta, yellow, and black channel. A CMYK image is generally used to print a colour separation.

Colour correction
The changing of the colours of pixels in an image, including adjusting brightness, contrast, mid-level grays, hue, and saturation to achieve optimum printed results.

Colour proof
A representation of the final printed product, for checking colour accuracy and other elements.

Colour separation
The process of splitting full-colour artwork into its CMYK components; one or all four of the separate pieces of film from which a four-colour version will be printed.

Continuous-tone image
An image containing gradient tones from black to white.

Contrast
The tonal gradation between the highlights, mid-tones, and shadows in an image.

DCS Desktop Colour Separation
A file format that creates four colour separations

DPI
Dots per inch: a measure of image resolution.

Four-colour process printing
The basic method of recreating a broad spectrum of colours on a printing press.

Grayscale image
An image consisting of up to 256 levels or gray, with 8 bits of colour data per pixel.

Halftone
The reproduction of a continuous-tone image, made by using a screen that breaks the image into various size dots.

Highlight
The lightest part of an image, represented in a halftone by the smallest dots, or the absence of dots.

Hue
The main attribute of a colour that distinguishes it from other colours

Image resolution
The amount of data stored in an image file, measured in pixels per inch (ppi).

JPEG
Joint Photographic Experts Group. This group established a standard method for compressing and decompressing digitised photos or images. The high-resolution images provided with Photo Disc are compressed according to JPEG standards.

LPI
Lines per inch.
A measure of resolution, usually screen frequency in halftones.

Luminance
Lightness. The highest of the individual RGB values plus the lowest of the individual RGB values, divided by two; a component of a Hue-Saturation-Lightness image.

Mid tone
Tonal value of dot, located approximately halfway between the highlight value and the shadow value.

Moiré pattern
An undesirable pattern in colour printing, resulting from incorrect screen angles of overprinting halftones. Moiré patterns can be minimized with the use of proper screen angles.

Pixel
A single dot on a computer display or in a digital image.

PICT
A standard file format for exchanging graphics or image information.

PPI
Pixels per inch, a measure of the resolution of a computer display or digital image.

Printer resolution
The amount of detail a printer or image-setter will reproduce, measured in dots per inch (dpi).

Process colour
The four colour pigments cyan, magenta, yellow, and black used in colour printing.

Resample
To change the resolution of an image. Re-sampling down discards pixel information in an image; re-sampling up adds pixel information through interpolation.

Resolution
The number of pixels per inch in an image, or the number of dots per inch used by an output device.

RGB
Red, green, and blue, the additive primaries; RGB is the basic additive colour model used for colour video display, as on a computer monitor.

Saturation
The amount of gray in a colour More gray in a colour means lower saturation; less gray in a colour means higher saturation.

Screen angle
The angle at which the halftone screens are placed in relation to one another.

Screen frequency
The density of dots on the halftone screen, commonly measured in lines per inch (lpi). Also known an screen ruling.

Shadow
The darkest part of an image, represented in a halftone by the largest dots.

Thumbnails
Miniature pictures, resembling slides, that the Light-Box catalog displays. Each thumbnail contains specific information for each image that comes with Photo-Disc.

TIFF
Tagged Image File Format, a file format for exchanging bitmapped and grayscale images among applications.


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