Glossary of "Portable Network Graphics (PNG) Specification (Second Edition)"

Term entries in the "Portable Network Graphics (PNG) Specification (Second Edition)" glossary

W3C Glossaries

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greyscale

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

image representation in which each pixel is defined by a single sample of colour information, representing overall luminance (on a scale from black to white), and optionally an alpha sample (in which case it is called greyscale with alpha).

image data

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

1-dimensional array of scanlines within an image.

indexed-colour

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

image representation in which each pixel of the original image is represented by a single index into a palette . The selected palette entry defines the actual colour of the pixel.

indexing

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

representing an image by a palette , an alpha table , and an array of indices pointing to entries in the palette and alpha table.

interlaced PNG image

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

sequence of reduced images generated from the PNG image by pass extraction .

lossless compression

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

method of data compression that permits reconstruction of the original data exactly, bit-for-bit.

lossy compression

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

method of data compression that permits reconstruction of the original data approximately, rather than exactly.

luminance

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

formal definition of luminance is in [CIE-15.2] . Informally it is the perceived brightness, or greyscale level, of a colour. Luminance and chromaticity together fully define a perceived colour.

LZ77

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

data compression algorithm described by Ziv and Lempel in their 1977 paper [ZL] .

network byte order

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

byte order in which the most significant byte comes first, then the less significant bytes in descending order of significance ( MSB LSB for two-byte integers, MSB B2 B1 LSB for four-byte integers).

palette

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

indexed table of three 8-bit sample values, red, green, and blue, which with an indexed-colour image defines the red, green, and blue sample values of the reference image . In other cases, the palette may be a suggested palette that viewers may use to present the image on indexed-colour display hardware. Alpha samples may be defined for palette entries via the alpha table and may be used to reconstruct the alpha sample values of the reference image.

pass extraction

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

organizing a PNG image as a sequence of reduced images to change the order of transmission and enable progressive display.

pixel

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

information stored for a single grid point in an image. A pixel consists of (or points to) a sequence of samples from all channels . The complete image is a rectangular array of pixels.

PNG datastream

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

result of encoding a PNG image . A PNG datastream consists of a PNG signature followed by a sequence of chunks .

PNG decoder

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

process or device which reconstructs the reference image from a PNG datastream and generates a corresponding delivered image.

PNG editor

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

process or device which creates a modification of an existing PNG datastream , preserving unmodified ancillary information wherever possible, and obeying the chunk ordering rules, even for unknown chunk types.

PNG encoder

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

process or device which constructs a reference image from a source image , and generates a PNG datastream representing the reference image.

PNG file

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

PNG datastream stored as a file.

PNG four-byte signed integer

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

a four-byte signed integer limited to the range -(2 ³¹ -1) to 2 ³¹ -1. The restriction is imposed in order to accommodate languages that have difficulty with the value -2 ³¹ .

PNG four-byte unsigned integer

From Portable Network Graphics (PNG) Specification (Second Edition) (2003-11-10)

a four-byte unsigned integer limited to the range 0 to 2 ³¹ -1. The restriction is imposed in order to accommodate languages that have difficulty with unsigned four-byte values.

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