美文网首页
【色度学】HSP 色彩空间

【色度学】HSP 色彩空间

作者: 罗引杰 | 来源:发表于2020-10-15 17:26 被阅读0次

    由于HSL 和 HSV 的值并不能反应人眼看到的真实亮度(如下图),实际上人眼看青色会很亮, 但是在HSV模型中, 青色表现的亮度和蓝色一样, 为了解决这种亮度表示问题,所以引入了HSP色彩空间, 以反应人眼看到的真实的颜色;

    image.png

    HSP 的亮度公式定义为:


    image.png

    互转公式:

    
    //如果是BT709 或 sRGB 色域参数如下, 不同的色域使用不同的Pr Pg Pb
    #define  Pr  .299
    #define  Pg  .587
    #define  Pb  .114
    
    
    
    //  public domain function by Darel Rex Finley, 2006
    //
    //  This function expects the passed-in values to be on a scale
    //  of 0 to 1, and uses that same scale for the return values.
    //
    //  See description/examples at alienryderflex.com/hsp.html
    
    void RGBtoHSP(
    double  R, double  G, double  B,
    double *H, double *S, double *P) {
    
      //  Calculate the Perceived brightness.
      *P=sqrt(R*R*Pr+G*G*Pg+B*B*Pb);
    
      //  Calculate the Hue and Saturation.  (This part works
      //  the same way as in the HSV/B and HSL systems???.)
      if      (R==G && R==B) {
        *H=0.; *S=0.; return; }
      if      (R>=G && R>=B) {   //  R is largest
        if    (B>=G) {
          *H=6./6.-1./6.*(B-G)/(R-G); *S=1.-G/R; }
        else         {
          *H=0./6.+1./6.*(G-B)/(R-B); *S=1.-B/R; }}
      else if (G>=R && G>=B) {   //  G is largest
        if    (R>=B) {
          *H=2./6.-1./6.*(R-B)/(G-B); *S=1.-B/G; }
        else         {
          *H=2./6.+1./6.*(B-R)/(G-R); *S=1.-R/G; }}
      else                   {   //  B is largest
        if    (G>=R) {
          *H=4./6.-1./6.*(G-R)/(B-R); *S=1.-R/B; }
        else         {
          *H=4./6.+1./6.*(R-G)/(B-G); *S=1.-G/B; }}}
    
    
    
    //  public domain function by Darel Rex Finley, 2006
    //
    //  This function expects the passed-in values to be on a scale
    //  of 0 to 1, and uses that same scale for the return values.
    //
    //  Note that some combinations of HSP, even if in the scale
    //  0-1, may return RGB values that exceed a value of 1.  For
    //  example, if you pass in the HSP color 0,1,1, the result
    //  will be the RGB color 2.037,0,0.
    //
    //  See description/examples at alienryderflex.com/hsp.html
    
    void HSPtoRGB(
    double  H, double  S, double  P,
    double *R, double *G, double *B) {
    
      double  part, minOverMax=1.-S ;
    
      if (minOverMax>0.) {
        if      ( H<1./6.) {   //  R>G>B
          H= 6.*( H-0./6.); part=1.+H*(1./minOverMax-1.);
          *B=P/sqrt(Pr/minOverMax/minOverMax+Pg*part*part+Pb);
          *R=(*B)/minOverMax; *G=(*B)+H*((*R)-(*B)); }
        else if ( H<2./6.) {   //  G>R>B
          H= 6.*(-H+2./6.); part=1.+H*(1./minOverMax-1.);
          *B=P/sqrt(Pg/minOverMax/minOverMax+Pr*part*part+Pb);
          *G=(*B)/minOverMax; *R=(*B)+H*((*G)-(*B)); }
        else if ( H<3./6.) {   //  G>B>R
          H= 6.*( H-2./6.); part=1.+H*(1./minOverMax-1.);
          *R=P/sqrt(Pg/minOverMax/minOverMax+Pb*part*part+Pr);
          *G=(*R)/minOverMax; *B=(*R)+H*((*G)-(*R)); }
        else if ( H<4./6.) {   //  B>G>R
          H= 6.*(-H+4./6.); part=1.+H*(1./minOverMax-1.);
          *R=P/sqrt(Pb/minOverMax/minOverMax+Pg*part*part+Pr);
          *B=(*R)/minOverMax; *G=(*R)+H*((*B)-(*R)); }
        else if ( H<5./6.) {   //  B>R>G
          H= 6.*( H-4./6.); part=1.+H*(1./minOverMax-1.);
          *G=P/sqrt(Pb/minOverMax/minOverMax+Pr*part*part+Pg);
          *B=(*G)/minOverMax; *R=(*G)+H*((*B)-(*G)); }
        else               {   //  R>B>G
          H= 6.*(-H+6./6.); part=1.+H*(1./minOverMax-1.);
          *G=P/sqrt(Pr/minOverMax/minOverMax+Pb*part*part+Pg);
          *R=(*G)/minOverMax; *B=(*G)+H*((*R)-(*G)); }}
      else {
        if      ( H<1./6.) {   //  R>G>B
          H= 6.*( H-0./6.); *R=sqrt(P*P/(Pr+Pg*H*H)); *G=(*R)*H; *B=0.; }
        else if ( H<2./6.) {   //  G>R>B
          H= 6.*(-H+2./6.); *G=sqrt(P*P/(Pg+Pr*H*H)); *R=(*G)*H; *B=0.; }
        else if ( H<3./6.) {   //  G>B>R
          H= 6.*( H-2./6.); *G=sqrt(P*P/(Pg+Pb*H*H)); *B=(*G)*H; *R=0.; }
        else if ( H<4./6.) {   //  B>G>R
          H= 6.*(-H+4./6.); *B=sqrt(P*P/(Pb+Pg*H*H)); *G=(*B)*H; *R=0.; }
        else if ( H<5./6.) {   //  B>R>G
          H= 6.*( H-4./6.); *B=sqrt(P*P/(Pb+Pr*H*H)); *R=(*B)*H; *G=0.; }
        else               {   //  R>B>G
          H= 6.*(-H+6./6.); *R=sqrt(P*P/(Pr+Pb*H*H)); *B=(*R)*H; *G=0.; }}}
    
    

    参考资料:
    http://alienryderflex.com/hsp.html

    相关文章

      网友评论

          本文标题:【色度学】HSP 色彩空间

          本文链接:https://www.haomeiwen.com/subject/zkeopktx.html