143 lines
3.9 KiB
Groff
143 lines
3.9 KiB
Groff
.TH IM_XYZ2disp 3 "2 Decemder 1992"
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.SH NAME
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im_XYZ2disp, im_disp2XYZ, im_Lab2XYZ, im_XYZ2Lab, im_XYZ2Yxy, im_Yxy2XYZ,
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im_XYZ2sRGB, im_sRGB2XYZ,
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im_Lab2LCh, im_LCh2Lab, im_LCh2UCS, im_UCS2LCh \- convert images between
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various colour spaces
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.SH SYNOPSIS
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#include <vips/vips.h>
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int im_XYZ2disp(in, out, display)
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.br
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IMAGE *in, *out;
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.br
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struct im_col_display *display;
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int im_disp2XYZ(in, out, display)
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.br
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IMAGE *in, *out;
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.br
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struct im_col_display *display;
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int im_Lab2XYZ(in, out)
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.br
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IMAGE *in, *out;
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int im_XYZ2Lab(in, out)
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.br
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IMAGE *in, *out;
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int im_XYZ2Yxy(in, out)
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.br
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IMAGE *in, *out;
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int im_Yxy2XYZ(in, out)
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.br
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IMAGE *in, *out;
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int im_XYZ2sRGB(in, out)
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.br
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IMAGE *in, *out;
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int im_sRGB2XYZ(in, out)
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.br
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IMAGE *in, *out;
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int im_Lab2LCh(in, out)
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.br
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IMAGE *in, *out;
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int im_LCh2Lab(in, out)
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.br
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IMAGE *in, *out;
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int im_LCh2UCS(in, out)
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.br
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IMAGE *in, *out;
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int im_UCS2LCh(in, out)
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.br
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IMAGE *in, *out;
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.SH DESCRIPTION
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Functions to convert images between the different colour spaces supported by
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VIPS: RGB, sRGB, XYZ, Yxy, Lab, LCh and UCS. RGB and sRGB are three band uchar
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files. XYZ, Lab, LCh and UCS are three band float files.
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These are the basic conversion routines provided by VIPS. Other conversions,
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such as im_Lab2disp(3), are built by composing these functions and are provided
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as a convenience to the programmer.
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The VIPS colour spaces inter-convert as follows:
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+------- sRGB
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LabQ ----- Lab ----- XYZ ----- RGB
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| | +------- Yxy
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| +------- LCh ----- UCS
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+-------- LabS
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The colour spaces are:
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LabQ --- This is the principal VIPS colorimetric storage format. See
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im_LabQ2Lab(3) for an explanation. You cannot perform calculations on LabQ
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images. They are for storage only.
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LabS --- This format represents coordinates in CIE Lab space as 16-bit
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integers. It is the best format for computation, being relatively compact,
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quick, and accurate. Colour values expressed in this way are hard to
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visualise. See the page for im_LabQ2LabS().
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Lab --- Coordinates in CIE Lab space are represented as float values in the
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usual range. This is the easiest format for general work: adding 50 to the L
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channel, for example, has the expected result.
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XYZ --- CIE XYZ colour space.
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Yxy --- CIE Yxy colour space.
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RGB --- This format is compatible with the RGB colour systems used in other
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packages. If you want to export your image to a PC, for example, convert your
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colorimetric image to RGB, then turn it to TIFF with vips2TIFF(1). You need to
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supply a structure which characterises your display. See the manual page for
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im_col_XYZ2rgb(3) for hints on these guys.
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sRGB --- This is a standard RGB, as defined by:
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http://www.color.org/contrib/sRGB.html
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it's handy for carrying colour information through JPEG compressors, for
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example.
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LCh --- Like Lab, but the rectangular ab coordinates are replaced with the
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polar Ch (Chroma and hue) coordinates. Hue angles are expressed in degrees.
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UCS --- A colour space based on the CMC(1:1) colour difference measurement.
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This is a highly uniform colour space, much better than Lab for expressing
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small differences. Conversions to and from UCS are extremely slow.
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These conversions set the Type field in the image header to LABQ, LABS, LAB,
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XYZ, RGB, sRGB, LCH and UCS respectively. The Type field is for user
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information only --- no function reads the Type field to determine its
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behaviour. Visualisation programs, such as ip(1), use the Type field to help
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present the information to the user.
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All VIPS colour spaces are based around D65.
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VIPS has functions for finding colour difference images. See
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im_dE_fromLab(3).
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.SH RETURN VALUE
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The functions return 0 on success and -1 on error.
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.SH SEE ALSO
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im_col_XYZ2rgb(3), im_dE_fromLab(3), im_LabQ2Lab(3), im_Lab2disp(3).
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.SH COPYRIGHT
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National Gallery and Birkbeck College, 1990 - 1993
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.SH AUTHOR
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K. Martinez \- 2/12/1992
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.br
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J. Cupitt \- 21/7/93
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