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diff --git a/doc/info/chap/colour-spaces.texinfo b/doc/info/chap/colour-spaces.texinfo new file mode 100644 index 0000000..5c88a88 --- /dev/null +++ b/doc/info/chap/colour-spaces.texinfo @@ -0,0 +1,765 @@ +@node Colour Spaces +@chapter Colour Spaces + +@menu +* RGB:: Generic RGB colour spaces. +* sRGB:: The Standard RGB colour space. +* CIExyY:: The CIE xyY colour model. +* CIEXYZ:: The CIE 1931 XYZ colour model. +* CIELAB:: The CIE L*a*b* colour model. +* CIELUV:: The CIE 1976 (L*, u*, v*) colour model. +* CIELCh:: The CIE LCh colour model. +* YIQ:: The YIQ colour model. +* YDbDr:: The YDbDr colour model. +* YUV:: The YUV colour model. +* YPbPr:: The YPbPr colour model. +* YCgCo:: The YCgCo colour model. +* CIE 1960 UCS:: The CIE 1960 UCS colour model. +* CIEUVW:: The CIE 1964 (U*, V*, W*) colour model. +@end menu + + + +A colour in @command{libcolour} is represented using + +@example +typedef union libcolour_colour @{ + enum libcolour_model model; + struct libcolour_rgb rgb; + struct libcolour_srgb srgb; + struct libcolour_ciexyy ciexyy; + struct libcolour_ciexyz ciexyz; + struct libcolour_cielab cielab; + struct libcolour_cieluv cieluv; + struct libcolour_cielch cielch; + struct libcolour_yiq yiq; + struct libcolour_ydbdr ydbdr; + struct libcolour_yuv yuv; + struct libcolour_ypbpr ypbpr; + struct libcolour_ycgco ycgco; + struct libcolour_cie1960ucs cie1960ucs; + struct libcolour_cieuvw cieuvw; +@} libcolour_colour_t; +@end example + +@noindent +where @code{.model} is used to select colour model. +Each @code{enum} and @code{struct} is also @code{typedef}:ed +to the same name but with an @code{_t} suffix. + +The macro @code{LIBCOLOUR_LIST_MODELS} can be used to list +all available colour models. It expands to a list of +calls to @code{X} with the appropriate value for @code{.model} +as the first argument and the @code{struct}, using the +@code{typedef} name with the @code{_t} suffix, which is used +to represent colours in that colour model as the second +argument. It can used like this: + +@example +void print_libcolour_srgb_t(libcolour_srgb* colour) +@{ + printf("sRGB(%lf, %lf, %lf, with_gamma = %i)\n", + colour->R, colour->G, colour->B, colour->with_gamma); +@} + +/* ... */ + +void print_colour(libcolour_colour_t* colour) +@{ +#define X(MODEL, TYPE)\ + case MODEL:\ + print_##TYPE((TYPE*)colour);\ + break; +#undef X + switch (colour->model) @{ + LIBCOLOUR_LIST_MODELS + default: + printf("Unknown colour model!\n"); + break; + @} +@} +@end example + +To convert between a colour into another colour space, +the function @code{libcolour_convert} is used. It takes +two arguments, both if the type @code{libcolour_colour_t*}. +The first parameter is @code{const}, it shall be the +colour you want to convert. The second parameter shall +be a different pointer, and it shall have it's @code{.model} +set to the wanted colour model, and any colour space +specific parameter for that model shall also be set. It +can be used like this: + +@example +int to_srgb(const libcolour_colour* from, libcolour_srgb_t* to) +@{ + to->model = LIBCOLOUR_SRGB; + to->with_gamma = 1; + return libcolour_convert(from, to); +@} +@end example + +@code{libcolour_convert} return 0 on success, on error @math{-1} +is returned and @code{errno} is to indicate the error. Possible +errors are: +@table @code +@item EINVAL +Invalid colour model. +@end table + +Colours obtained by conversion can be out of gamut. In RGB +colour spaces, including sRGB, this means that at least one +of the values (@code{.R}, @code{.G}, or @code{.B}) is less +than 0 or greater than 1. @command{libcolour} does not provide +any colour-matching functions for finding an in-gamut colour. + + + +@node RGB +@section Generic RGB + +RGB colours, of any RGB colour space, are presented with +@code{struct libcolour_rgb} (@code{libcolour_rgb_t}), and the +@code{.model} member shall be set to @code{LIBCOLOUR_RGB}. In +@code{union libcolour_colour}, @code{.rgb} are used for RGB +colours. RGB colours are additive. + +@code{struct libcolour_rgb} has the following members +@table @code +@item enum libcolour_model model +Shall be set to @code{LIBCOLOUR_RGB}. +@item double R +The red value. In-gamut values are between 0 and 1, inclusively. +@item double G +The green value. In-gamut values are between 0 and 1, inclusively. +@item double B +The blue value. In-gamut values are between 0 and 1, inclusively. +@item int with_gamma +Whether the the transfer function is applied to the values +of @code{.R}, @code{.G}, and @code{.B}, which makes them non-linear. +@item enum libcolour_encoding_type encoding_type +One of the following: +@table @code +@item LIBCOLOUR_ENCODING_TYPE_LINEAR +The colour space does not have a transfer function. +@item LIBCOLOUR_ENCODING_TYPE_SIMPLE +The colour space uses a simple gamma transfer function +that only uses the gamma parameter. +@item LIBCOLOUR_ENCODING_TYPE_REGULAR +The colour space uses a linear–gamma hybrid transfer +function that uses the gamma, offset, slope, and +transition parameters. +@item LIBCOLOUR_ENCODING_TYPE_CUSTOM +The colour space uses a custom transfer function. +@end table +@item double gamma +The gamma parameter of the transfer function. +Ignored unless @code{.encoding_type} is +@code{LIBCOLOUR_ENCODING_TYPE_SIMPLE} or +@code{LIBCOLOUR_ENCODING_TYPE_REGULAR}. +@item double offset +The offset parameter of the transfer function. +Ignored unless @code{.encoding_type} is +@code{LIBCOLOUR_ENCODING_TYPE_REGULAR}. +@item double slope +The slope parameter of the transfer function. +Ignored unless @code{.encoding_type} is +@code{LIBCOLOUR_ENCODING_TYPE_REGULAR}. +@item double transition +The transition parameter of the transfer +function. Ignored unless @code{.encoding_type} +is @code{LIBCOLOUR_ENCODING_TYPE_REGULAR}. +@item double transitioninv +The inverse value of the transition parameter +of the transfer function, that is, where the +transition takes place in the encoded, rather +than linear, values. This value is set +automatically. Ignored unless @code{.encoding_type} +is @code{LIBCOLOUR_ENCODING_TYPE_REGULAR}. +@item double (*to_encoded_red)(double) +Function used to apply the red channels transfer function +to a value. Ignored unless @code{.encoding_type} is +@code{LIBCOLOUR_ENCODING_TYPE_CUSTOM}. +@item double (*to_decoded_red)(double) +Function used to unapply the red channels transfer function +from a value. Ignored unless @code{.encoding_type} is +@code{LIBCOLOUR_ENCODING_TYPE_CUSTOM}. +@item double (*to_encoded_green)(double) +Function used to apply the green channels transfer function +to a value. Ignored unless @code{.encoding_type} is +@code{LIBCOLOUR_ENCODING_TYPE_CUSTOM}. +@item double (*to_decoded_green)(double) +Function used to unapply the green channels transfer function +from a value. Ignored unless @code{.encoding_type} is +@code{LIBCOLOUR_ENCODING_TYPE_CUSTOM}. +@item double (*to_encoded_blue)(double) +Function used to apply the blue channels transfer function +to a value. Ignored unless @code{.encoding_type} is +@code{LIBCOLOUR_ENCODING_TYPE_CUSTOM}. +@item double (*to_decoded_blue)(double) +Function used to unapply the blue channels transfer function +from a value. Ignored unless @code{.encoding_type} is +@code{LIBCOLOUR_ENCODING_TYPE_CUSTOM}. +@item struct libcolour_ciexyy red +The CIE xyY value of the red primarily. +@item struct libcolour_ciexyy green +The CIE xyY value of the green primarily. +@item struct libcolour_ciexyy blue +The CIE xyY value of the blue primarily. +@item struct libcolour_ciexyy white +The CIE xyY value of the white point, the Y value +should usually be 1. +@item double white_r +The red value of the white point, should usually by 1. +@item double white_g +The green value of the white point, should usually by 1. +@item double white_b +The blue value of the white point, should usually by 1. +@item double M[3][3] +Matrix used to convert a colour to CIE 1931 XYZ. +@item double Minv[3][3] +Matrix used to convert a colour from CIE 1931 XYZ. +@item enum libcolour_rgb_colour_space colour_space +The colour space. Set automatically. +@end table + +@code{libcolour_get_rgb_colour_space} is set the +values in a @code{libcolour_rgb_t} to the those used +to represent a specified RGB colour space. +@code{libcolour_get_rgb_colour_space} has two arguments: +@table @code +@item libcolour_rgb_t* +The @code{struct} whose members shall be set to represent +to selected colour space. +@item enum libcolour_rgb_colour_space +The selected colour space. +@end table + +@code{libcolour_get_rgb_colour_space} return 0 on success, +on error @math{-1} is returned and @code{errno} is to indicate +the error. Possible errors are: +@table @code +@item EINVAL +Invalid colour space. +@item EDOM +The specified colour space parameters cannot be used +as it results in matematical errors. +@end table + +The following values are available for +@code{enum libcolour_rgb_colour_space} (@code{libcolour_rgb_colour_space_t}): + +@table @code +@item LIBCOLOUR_RGB_COLOUR_SPACE_CUSTOM_FROM_MEASUREMENTS +A custom colour space. @code{.red}, @code{.green}, @code{.blue}, +@code{.white}, @code{.white_r}, @code{.white_g} and @code{.white_b} +must be set. The transfer functions, and parameters, must be set +manually. @code{.colour_space} must be set to any negative value, +@code{LIBCOLOUR_RGB_COLOUR_SPACE_CUSTOM_FROM_MEASUREMENTS} (zero), +@code{LIBCOLOUR_RGB_COLOUR_SPACE_CUSTOM_FROM_MATRIX}, or +@code{LIBCOLOUR_RGB_COLOUR_SPACE_CUSTOM_FROM_INV_MATRIX}. +@code{.red.Y}, @code{.green.Y}, @code{.blue.Y} can be any value. +@item LIBCOLOUR_RGB_COLOUR_SPACE_CUSTOM_FROM_MATRIX +A custom colour space. @code{.M}, @code{.white_r}, @code{.white_g} +and @code{.white_b} must be set. The transfer functions, and +parameters, must be set manually. @code{.colour_space} must be +set to any negative value, +@code{LIBCOLOUR_RGB_COLOUR_SPACE_CUSTOM_FROM_MEASUREMENTS} (zero), +@code{LIBCOLOUR_RGB_COLOUR_SPACE_CUSTOM_FROM_MATRIX}, or +@code{LIBCOLOUR_RGB_COLOUR_SPACE_CUSTOM_FROM_INV_MATRIX}. +@item LIBCOLOUR_RGB_COLOUR_SPACE_CUSTOM_FROM_INV_MATRIX +A custom colour space. @code{.Minv}, @code{.white_r}, @code{.white_g} +and @code{.white_b} must be set. The transfer functions, and +parameters, must be set manually. @code{.colour_space} must be +set to any negative value, +@code{LIBCOLOUR_RGB_COLOUR_SPACE_CUSTOM_FROM_MEASUREMENTS} (zero), +@code{LIBCOLOUR_RGB_COLOUR_SPACE_CUSTOM_FROM_MATRIX}, or +@code{LIBCOLOUR_RGB_COLOUR_SPACE_CUSTOM_FROM_INV_MATRIX}. +@item LIBCOLOUR_RGB_COLOUR_SPACE_SRGB +The sRGB colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_ADOBE_RGB +The Adobe RGB colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_APPLE_RGB +The Apple RGB (1998) colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_BEST_RGB +The Best RGB colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_BETA_RGB +The Beta RGB colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_BRUCE_RGB +The Bruce RGB colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_CIE_RGB +The CIE 1931 RGB colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_COLORMATCH_RGB +The ColorMatch RGB colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_DCI_P3_D65 +The DCI-P3 D65 colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_DCI_P3_THEATER +The DCI-P3 Theater colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_DON_RGB_4 +The Don RGB 4 colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_ECI_RGB_V2 +The ECI RGB v2 colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_EKTA_SPACE_PS5 +The Ekta Space PS5 colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_ITU_R_BT_601_625_LINE +The ITU-R Recommendation BT.601, 625 line colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_ITU_R_BT_601_525_LINE +The ITU-R Recommendation BT.601, 525 line colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_ITU_R_BT_709 +The ITU-R Recommendation BT.709 colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_ITU_R_BT_2020 +The ITU-R Recommendation BT.2020 colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_ITU_R_BT_2100_EOTF_PQ +The ITU-R Recommendation BT.2100 colour space, +using the perceptual quantization (PQ) elctro-optical +transfer function (EOTF). +@item LIBCOLOUR_RGB_COLOUR_SPACE_ITU_R_BT_2100_OOTF_PQ +The ITU-R Recommendation BT.2100 colour space, +using the perceptual quantization (PQ) opto-optical +transfer function (OOTF). +@item LIBCOLOUR_RGB_COLOUR_SPACE_ITU_R_BT_2100_OETF_PQ +The ITU-R Recommendation BT.2100 colour space, +using the perceptual quantization (PQ) opto-electronic +transfer function (OETF). +@item LIBCOLOUR_RGB_COLOUR_SPACE_ITU_R_BT_2100_EOTF_HLG +The ITU-R Recommendation BT.2100 colour space, +using the Hybrid Log-Gamma (HLG) elctro-optical +transfer function (EOTF). +@item LIBCOLOUR_RGB_COLOUR_SPACE_ITU_R_BT_2100_OOTF_HLG +The ITU-R Recommendation BT.2100 colour space, +using the Hybrid Log-Gamma (HLG) opto-optical +transfer function (OOTF). +@item LIBCOLOUR_RGB_COLOUR_SPACE_ITU_R_BT_2100_OETF_HLG +The ITU-R Recommendation BT.2100 colour space, +using the Hybrid Log-Gamma (HLG) opto-electronic +transfer function (OETF). +@item LIBCOLOUR_RGB_COLOUR_SPACE_LIGHTROOM_RGB +The Lightroom RGB colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_NTSC_RGB +The NTSC RGB colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_PAL_SECAM_RGB +The PAL/SECAM RGB colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_PROPHOTO_RGB +The ProPhoto RGB colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_SGI_RGB +The SGI RGB colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_SMPTE_240M_RGB +The SMPTE 240M RGB colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_SMPTE_C_RGB +The SMPTE C RGB colour space. +@item LIBCOLOUR_RGB_COLOUR_SPACE_WIDE_GAMUT_RGB +The wide-gamut RGB colour space, also known as +Adobe Wide Gamut RGB. +@end table + +Call @code{libcolour_proper(&c)} on a +@code{struct libcolour_rgb_t c} (done automatically for +predefined colour spaces) sets @code{c.red.model}, +@code{c.green.model}, and @code{c.blue.model} to +@code{LIBCOLOUR_CIEXYY}, and calculate and sets the Y +values for @code{c.red}, @code{c.green}, and @code{c.blue}. +Zero is always normally returned, but of there is something +wrong with with the values of the primaries, @math{-1} +is returned and @code{errno} is set to @code{EDOM}. + + + +@node sRGB +@section Standard RGB + +sRGB colours are presented with @code{struct libcolour_srgb} +(@code{libcolour_srgb_t}), and the @code{.model} member shall +be set to @code{LIBCOLOUR_SRGB}. In @code{union libcolour_colour}, +@code{.srgb} are used for sRGB colours. This is the colour model +and colour space normally used on computers, it is however not +the colour space your monitor have, although it is close to it. +sRGB is designed after the human eye, but fails to take into +account how the brain process the input to figure out which +colour it actually receives. + +@code{struct libcolour_srgb} has the following members +@table @code +@item enum libcolour_model model +Shall be set to @code{LIBCOLOUR_SRGB}. +@item double R +The red value. In-gamut values are between 0 and 1, inclusively. +@item double G +The green value. In-gamut values are between 0 and 1, inclusively. +@item double B +The blue value. In-gamut values are between 0 and 1, inclusively. +@item int with_gamma +Whether the the transfer function is applied to the values of +@code{.R}, @code{.G}, and @code{.B}, which makes them non-linear. +@end table + +The RGB color model, of which sRGB is a specific colour space, +is an additive colour model. + +For your convenience, the sRGB transfer function and its inverse +function is available for your use: + +@table @code +@item double libcolour_srgb_encode(double x) +Applies the sRGB transfer function. +It's full code is +@example +return x <= 0.0031306684425217108 + ? 12.92 * x + : 1.055 * pow(x, 1 / 2.4) - 0.055; +@end example + +@item double libcolour_srgb_decode(double x) +Unapplies the sRGB transfer function. +It's full code is +@example +return x <= 0.040448236277380506 + ? x / 12.92 + : pow((x + 0.055) / 1.055, 2.4); +@end example +@end table + + + +@node CIExyY +@section CIE xyY + +CIE xyY colours are presented with @code{struct libcolour_ciexyy} +(@code{libcolour_ciexyy_t}), and the @code{.model} member shall +be set to @code{LIBCOLOUR_CIEXYY}. In @code{union libcolour_colour}, +@code{.ciexyy} are used for CIE xyY colours. This colour space is +derived from CIE 1931 XYZ and is primarily used for representing +chromaticities. + +@code{struct libcolour_ciexyy} has the following members +@table @code +@item enum libcolour_model model +Shall be set to @code{LIBCOLOUR_CIEXYY}. +@item double x +The x value. +@item double y +The y value. +@item double Y +The Y value. +@end table + +CIE xyY is not additive. CIE xyY is defined by +@math{x = X/(X + Y + Z)}, @math{y = Y/(X + Y + Z)} +where X, Y, and Z are CIE XYZ values. + + +@node CIEXYZ +@section CIE 1931 XYZ + +CIE 1931 XYZ colours are presented with @code{struct libcolour_ciexyz} +(@code{libcolour_ciexyz_t}), and the @code{.model} member shall +be set to @code{LIBCOLOUR_CIEXYZ}. In @code{union libcolour_colour}, +@code{.ciexyz} are used for CIE 1931 XYZ colours. This colour space +is derived from CIE 1931 RGB and is used as an intermediary +representation when converting between many colour spaces and +colour models, making it very useful for device independent colour +representation. + +@code{struct libcolour_ciexyz} has the following members +@table @code +@item enum libcolour_model model +Shall be set to @code{LIBCOLOUR_CIEXYZ}. +@item double X +The X value. +@item double Y +The Y value. +@item double Z +The Z value. +@end table + +CIE 1931 XYZ is additive, since it is defined by matrix +multiplication with CIE 1932 RGB which is additive because +it is an RGB colour space. + + + +@node CIELAB +@section CIE L*a*b* + +CIE L*a*b* colours are presented with @code{struct libcolour_cielab} +(@code{libcolour_cielab_t}), and the @code{.model} member shall +be set to @code{LIBCOLOUR_CIELAB}. In @code{union libcolour_colour}, +@code{.cielab} are used for CIE L*a*b* colours. CIE L*a*b* +approximates human colour perception with a lightness parameter +(L*) and two chromaticity parameters (a* and b*), it is therefore +useful in image manipulation applications. + +@code{struct libcolour_cielab} has the following members +@table @code +@item enum libcolour_model model +Shall be set to @code{LIBCOLOUR_CIELAB}. +@item double L +The L* value. 0 is black, 100 is white. +@item double a +The a* value. Negative values are green, positive values are red. +@item double b +The b* value. Negative values are blue, positive values are yellow. +@end table + +CIE L*a*b* is not additive, since conversion from +CIE 1931 XYZ is non-linear. It's white point is the CIE Standard +Illuminant D50. + + + +@node CIELUV +@section CIE 1976 (L*, u*, v*) + +CIE 1976 (L*, u*, v*) colours are presented with @code{struct libcolour_cieluv} +(@code{libcolour_cieluv_t}), and the @code{.model} member shall be set to +@code{LIBCOLOUR_CIELUV}. In @code{union libcolour_colour}, @code{.cieluv} +are used for CIE 1976 (L*, u*, v*) colours. CIE 1976 (L*, u*, v*) +approximates uniform human colour perception. + +@code{struct libcolour_cieluv} has the following members +@table @code +@item enum libcolour_model model +Shall be set to @code{LIBCOLOUR_CIELUV}. +@item double L +The L* value. 0 is black, 100 is white. +@item double u +The u* value. +@item double v +The v* value. +@item struct libcolour_ciexyz white +The white point. +@end table + +CIE L*u*v* is not additive, since conversion from +CIE 1931 XYZ is non-linear. + +Call @code{libcolour_proper(&c)} on a +@code{struct libcolour_cieluv_t c} sets +@code{c.white.model} to @code{LIBCOLOUR_CIEXYZ}. +Zero is always returned in this case. + + + +@node CIELCh +@section CIE LCh@sub{uv} + +CIE LCh@sub{uv} (also known as CIE HLC@sub{uv}) colours are presented +with @code{struct libcolour_cielch} (@code{libcolour_cielch_t}), and +the @code{.model} member shall be set to @code{LIBCOLOUR_CIELCH}. In +@code{union libcolour_colour}, @code{.cielch} are used for CIE LCh@sub{uv} +colours. CIE LCh@sub{uv} approximates uniform human colour perception +using cylindrical representation. + +@code{struct libcolour_cielch} has the following members +@table @code +@item enum libcolour_model model +Shall be set to @code{LIBCOLOUR_CIELCH}. +@item double L +The L* value. 0 is black, 100 is white. +@item double C +@iftex +The @math{{\rm C}^{*}_{\rm uv}} value, the chroma. +@end iftex +@ifnottex +The C*@sub{uv} value, the chroma. +@end ifnottex +@item double h +The h@sub{uv} value, the hue. +@item struct libcolour_ciexyz white +The white point. +@end table + +CIE LCh@sub{uv} is not additive. It is a cylindrical +representation of CIE 1976 (L*, u*, v*). + +Call @code{libcolour_proper(&c)} on a +@code{struct libcolour_cielch_t c} sets +@code{c.white.model} to @code{LIBCOLOUR_CIEXYZ}. +Zero is always returned in this case. + + +@node YIQ +@section YIQ + +YIQ colours are presented with @code{struct libcolour_yiq} +(@code{libcolour_yiq_t}), and the @code{.model} member shall +be set to @code{LIBCOLOUR_YIQ}. In @code{union libcolour_colour}, +@code{.yiq} are used for YIQ colours. + +@code{struct libcolour_yiq} has the following members +@table @code +@item enum libcolour_model model +Shall be set to @code{LIBCOLOUR_YIQ}. +@item double Y +The Y value, the luma. 0 is black, 1 is white. +@item double I +The I (in-phase) value. Negative values are blue, positive values are orange. +@item double Q +The Q (quadrature) value. Negative values are green, positive values are purple. +@end table + +YIQ is additive, since conversion from CIE 1931 XYZ is done +with a matrix multiplication. It's white point is the CIE +Standard Illuminant D65. + + + +@node YDbDr +@section YDbDr + +YDbDr colours are presented with @code{struct libcolour_ydbdr} +(@code{libcolour_ydbdr_t}), and the @code{.model} member shall +be set to @code{LIBCOLOUR_YDBDR}. In @code{union libcolour_colour}, +@code{.ydbdr} are used for YDbDr colours. + +@code{struct libcolour_ydbdr} has the following members +@table @code +@item enum libcolour_model model +Shall be set to @code{LIBCOLOUR_YDBDR}. +@item double Y +The Y value, the luma. 0 is black, 1 is white. +@item double Db +The Db value. Difference (with a factor) between Y and blue. +@item double Dr +The Dr value. Difference (with a factor) between Y and red. +@end table + +YDbDr is additive, since conversion from CIE 1931 XYZ is done +with a matrix multiplication. It's white point is the CIE +Standard Illuminant D65. + + + +@node YUV +@section YUV + +YUV colours are presented with @code{struct libcolour_yuv} +(@code{libcolour_yuv_t}), and the @code{.model} member shall +be set to @code{LIBCOLOUR_YUV}. In @code{union libcolour_colour}, +@code{.yuv} are used for YUV colours. + +@code{struct libcolour_yuv} has the following members +@table @code +@item enum libcolour_model model +Shall be set to @code{LIBCOLOUR_YUV}. +@item double Y +The Y value, the luma. 0 is black, 1 is white. +@item double U +The U value. Difference (with a factor) between Y and blue. +@item double V +The V value. Difference (with a factor) between Y and red. +@end table + +YUV is additive, since conversion from YDbDr is done +with a diagonal matrix multiplication. It's white point is +the CIE Standard Illuminant D65. + + + +@node YPbPr +@section YP@sub{B}P@sub{R} + +YP@sub{B}P@sub{R} colours are presented with @code{struct libcolour_ypbpr} +(@code{libcolour_ypbpr_t}), and the @code{.model} member shall +be set to @code{LIBCOLOUR_YPBPR}. In @code{union libcolour_colour}, +@code{.ypbpr} are used for YP@sub{B}P@sub{R} colours. + +@code{struct libcolour_ypbpr} has the following members +@table @code +@item enum libcolour_model model +Shall be set to @code{LIBCOLOUR_YPBPR}. +@item double Y +The Y value, the luma. 0 is black, 1 is white. +@item double Pb +The P@sub{B} value. Difference between Y and blue. +@item double Pr +The P@sub{R} value. Difference between Y and red. +@end table + +YPbPr is additive, since conversion from CIE 1931 XYZ is done +with a matrix multiplication. It's white point is the CIE +Standard Illuminant D65. + + + +@node YCgCo +@section YCgCo + +YCgCo colours are presented with @code{struct libcolour_ycgco} +(@code{libcolour_ycgco_t}), and the @code{.model} member shall +be set to @code{LIBCOLOUR_YCGCO}. In @code{union libcolour_colour}, +@code{.ycgco} are used for YCgCo colours. + +@code{struct libcolour_ycgco} has the following members +@table @code +@item enum libcolour_model model +Shall be set to @code{LIBCOLOUR_YCGCO}. +@item double Y +The Y value, the luminance. 0 is black, 1 is white. +@item double Cg +The Cg (chrominance green) value. +@item double co +The Co (chrominance orange) value. +@end table + +YCgCo is additive, since conversion from CIE 1931 XYZ is done +with a matrix multiplication. It's white point is the CIE +Standard Illuminant D65. + + + +@node CIE 1960 UCS +@section CIE 1960 UCS + +CIE 1960 UCS colours are presented with @code{struct libcolour_cie1960ucs} +(@code{libcolour_cie1960ucs_t}), and the @code{.model} member shall +be set to @code{LIBCOLOUR_CIE1960UCS}. In @code{union libcolour_colour}, +@code{.cie1960ucs} are used for CIE 1960 UCS colours. + +@code{struct libcolour_cie1960ucs} has the following members +@table @code +@item enum libcolour_model model +Shall be set to @code{LIBCOLOUR_CIE1960UCS}. +@item double u +The u value. +@item double v +The v value. +@item double Y +The Y value, the luminance. +@end table + +CIE 1960 UCS is not additive. CIE 1960 UCS is defined by +@math{u = 4X/(X + 15Y + 3Z)}, @math{v = 6Y/(X + 15Y + 3Z)} +where X, Y, and Z are CIE XYZ values. + + + +@node CIEUVW +@section CIE 1964 (U*, V*, W*) + +CIE 1964 (U*, V*, W*) colours are presented with @code{struct libcolour_cieuvw} +(@code{libcolour_cieuvw_t}), and the @code{.model} member shall +be set to @code{LIBCOLOUR_CIEUVW}. In @code{union libcolour_colour}, +@code{.cieuvw} are used for CIE 1964 (U*, V*, W*) colours. + +@code{struct libcolour_cieuvw} has the following members +@table @code +@item enum libcolour_model model +Shall be set to @code{LIBCOLOUR_CIEUVW}. +@item double U +The U* value. +@item double V +The V* value. +@item double W +The W* value. +@item double u0 +The u' chromaticity coordinate of a ``specified white object''. +u' is defined as @math{4X/(X + 15Y + 3Z)} where X, Y, and Z +are CIE 1931 XYZ values. +@item double v0 +The v' chromaticity coordinate of a ``specified white object''. +u' is defined as @math{9Y/(X + 15Y + 3Z)} where X, Y, and Z +are CIE 1931 XYZ values. +@end table + +CIE 1960 UCS is not additive. + |