Function

Summary

Returns an external image containing color information from an image.

Package

graphics-ports

Signature

externalize-image gp image &key maximum-colors important-colors type quality &allow-other-keys => external-image

Arguments

gp

A CAPI pane.

image

An image.

maximum-colors

An integer or nil. The default is nil.

important-colors

An integer or nil

type

One of the keywords :bmp, :jpg, :jpeg, :png and :tiff. Other keywords may be supported, depending on the platform.

quality

An integer in the range [0,100].

Values

external-image

An external image.

Description

The function externalize-image returns an external-image containing color information from image .

If maximum-colors is nil or if the screen has no palette, an external-image using all the colors in image is created.

If maximum-colors is an integer, the external-image containing image will be created using no more than that number of colors. If the image contains more than maximum-colors colors, the maximum-colors most frequently used colors will be accurately stored; the remainder will be approximated by nearest colors out of the accurate ones, using internal Color System parameters as the weighting factors for the color distance.

The value of important-color is recorded in the external-image for later use, and specifies the number of colors required to draw a good likeness of the image. The default value is the number of colors in the image.

If type is supplied, it must be a keyword which specifies a known type, as returned by list-known-image-formats with for-writing-too t. The types :bmp, :jpg, :png and :tiff are known on all platforms (except Motif). Additionally, :jpeg is an as alias for :jpg.

quality is used for writing a JPG image on GTK+. It must be an integer in the inclusive range [0,100]. High values generate better images and larger files.

See also

make-image-from-port
write-external-image
Drawing - Graphics Ports