Man Linux: Main Page and Category List


       im_XYZ2disp,    im_disp2XYZ,    im_Lab2XYZ,   im_XYZ2Lab,   im_XYZ2Yxy,
       im_Yxy2XYZ,   im_XYZ2sRGB,   im_sRGB2XYZ,    im_Lab2LCh,    im_LCh2Lab,
       im_LCh2UCS, im_UCS2LCh - convert images between various colour spaces


       #include <vips/vips.h>

       int im_XYZ2disp(in, out, display)
       IMAGE *in, *out;
       struct im_col_display *display;

       int im_disp2XYZ(in, out, display)
       IMAGE *in, *out;
       struct im_col_display *display;

       int im_Lab2XYZ(in, out)
       IMAGE *in, *out;

       int im_XYZ2Lab(in, out)
       IMAGE *in, *out;

       int im_XYZ2Yxy(in, out)
       IMAGE *in, *out;

       int im_Yxy2XYZ(in, out)
       IMAGE *in, *out;

       int im_XYZ2sRGB(in, out)
       IMAGE *in, *out;

       int im_sRGB2XYZ(in, out)
       IMAGE *in, *out;

       int im_Lab2LCh(in, out)
       IMAGE *in, *out;

       int im_LCh2Lab(in, out)
       IMAGE *in, *out;

       int im_LCh2UCS(in, out)
       IMAGE *in, *out;

       int im_UCS2LCh(in, out)
       IMAGE *in, *out;


       Functions  to  convert  images  between  the  different  colour  spaces
       supported by VIPS: RGB, sRGB, XYZ, Yxy, Lab, LCh and UCS. RGB and  sRGB
       are  three band uchar files. XYZ, Lab, LCh and UCS are three band float

       These are  the  basic  conversion  routines  provided  by  VIPS.  Other
       conversions,  such  as  im_Lab2disp(3),  are  built  by composing these
       functions and are provided as a convenience to the programmer.

       The VIPS colour spaces inter-convert as follows:

                               +------- sRGB
         LabQ ----- Lab ----- XYZ ----- RGB
          |          |         |
          |          |         +------- Yxy
          |          |
          |          +------- LCh ----- UCS
          +-------- LabS

       The colour spaces are:

       LabQ --- This is the principal VIPS colorimetric  storage  format.  See
       im_LabQ2Lab(3)  for  an explanation. You cannot perform calculations on
       LabQ images. They are for storage only.

       LabS --- This format represents coordinates in CIE Lab space as  16-bit
       integers.  It  is  the  best  format  for computation, being relatively
       compact, quick, and accurate. Colour values expressed in this  way  are
       hard to visualise. See the page for im_LabQ2LabS().

       Lab --- Coordinates in CIE Lab space are represented as float values in
       the usual range. This is the easiest format for general work: adding 50
       to the L channel, for example, has the expected result.

       XYZ --- CIE XYZ colour space.

       Yxy --- CIE Yxy colour space.

       RGB  ---  This format is compatible with the RGB colour systems used in
       other packages. If you want to export your image to a PC, for  example,
       convert  your  colorimetric  image  to  RGB,  then turn it to TIFF with
       vips2TIFF(1). You need to supply a structure which  characterises  your
       display.  See  the manual page for im_col_XYZ2rgb(3) for hints on these

       sRGB --- This is a standard RGB, as defined by:

       it’s handy for carrying colour information  through  JPEG  compressors,
       for example.

       LCh  --- Like Lab, but the rectangular ab coordinates are replaced with
       the polar Ch (Chroma and hue) coordinates. Hue angles are expressed  in

       UCS  ---  A  colour  space  based  on  the  CMC(1:1)  colour difference
       measurement.  This is a highly uniform colour space, much  better  than
       Lab  for  expressing small differences. Conversions to and from UCS are
       extremely slow.

       These conversions set the Type field in the image header to LABQ, LABS,
       LAB,  XYZ,  RGB,  sRGB, LCH and UCS respectively. The Type field is for
       user information only --- no function reads the Type field to determine
       its  behaviour.   Visualisation  programs,  such as ip(1), use the Type
       field to help present the information to the user.

       All VIPS colour spaces are based around D65.

       VIPS  has  functions  for  finding  colour   difference   images.   See


       The functions return 0 on success and -1 on error.


       im_col_XYZ2rgb(3), im_dE_fromLab(3), im_LabQ2Lab(3), im_Lab2disp(3).


       National Gallery and Birkbeck College, 1990 - 1993


       K. Martinez - 2/12/1992
       J. Cupitt - 21/7/93

                                2 Decemder 1992                 IM_XYZ2disp(3)