Transform an image from the RGB color space to an arbitrary color space.

::trans_from_rgb transforms an image from the RGB color space to an arbitrary color space (ColorSpace). The three channels of the image are passed as three separate images on input and output.

The following transformations are supported:

  'yiq'
     |Y|   |0.299   0.587   0.144|   |R| 
     |I| = |0.595  -0.276  -0.333| * |G| 
     |Q|   |0.209  -0.522   0.287|   |B|  

  'argyb'
     |A |   |0.30   0.59   0.11|   |R|
     |Rg| = |0.50  -0.50   0.00| * |G|
     |Yb|   |0.25   0.25  -0.50|   |B|

  'ciexyz'
     |X|   |0.476   0.299   0.175|   |R|
     |Y| = |0.262   0.656   0.082| * |G|
     |Z|   |0.020   0.161   0.909|   |B| 

  'hls'
     min = min(R,G,B)
     max = max(R,G,B)
     L = (min + max) / 2
     if (max == min)
        H = 0
        S = 0
     else
        if (L > 0.5)
           S = (max - min) / (2 - max - min)
        else
           S = (max - min) / (max + min)
        fi
        if (R == max)
           H = ((G - B) / (max - min)) * 60
        elif (G == max)
           H = (2 + (B - R) / (max - min)) * 60
        elif (B == max)
           H = (4 + (R - G) / (max - min)) * 60
        fi
     fi

  'hsi'
     |M1|   |2/Sqrt(6)  -1/Sqrt(6)  -1/Sqrt(6)|   |R|
     |M2| = |0           1/Sqrt(2)  -1/Sqrt(2)| * |G|
     |I1|   |1/Sqrt(3)   1/Sqrt(3)   1/Sqrt(3)|   |B|
     H = ATan(M1/M2)
     S = Sqrt(Sqr(M1) + Sqr(M2))
     I = I1 * Sqrt(3)                                           

  'hsv'
     min = min(R,G,B)
     max = max(R,G,B)
     V = max
     if (max == min)
        S = 0
        H = 0
     else
        S = (max - min) / max
        if (R == max)
           H = ((G - B) / (max - min)) * 60
        elif (G == max)
           H = (2 + (B - R) / (max - min)) * 60
        elif (B == max)
           H = (4 + (R - G) / (max - min)) * 60
        fi
     fi

  'ihs'
     min = min(R,G,B)
     max = max(R,G,B)
     I = (R + G + B) / 3
     if (I == 0)
        H = 0
        S = 1
     else
        S = 1 - min / I
        if (S == 0)
           H = 0
        else
           A = (R + R - G - B) / 2
           B = (R - G) * (R - G) + (R - B) * (G - B)
           C = sqrt(B)
           if (C == 0)
              H = 0
           else
              H = acos(A / C)
           fi
           if (B > G)
              H = 2 * pi - H
           fi
        fi
     fi

  'isfeuklid'
     min = min(R,G,B)
     max = max(R,G,B)
     I = sqrt(R * R + G * G + B * B) / sqrt(3)
     if (I == 0)
        S = 0
        F = 0
     else
        S = acos(max(1, (R + G + B) / (I * 3))) / (pi / 2)
        if (R == min)
           F = acos(max(1, B / sqrt(G * G + B * B))) / (pi * 3 / 2) + 1 / 3
        elif (G == min)
           F = acos(max(1, R / sqrt(B * B + R * R))) / (pi * 3 / 2) + 2 / 3
        else
           F = acos(max(1, G / sqrt(R * R + G * G))) / (pi * 3 / 2)
        fi
     fi

  'isfdiff'
     if (R >= B && B >= G)
        I = R
        S = R - G
        F = (R - B) / 6
     elif (R >= G && G >= B)
        I = R
        S = R - B
        F = (2 - (R - G)) / 6
     elif (G >= R && R >= B)
        I = G
        S = G - B
        F = (2 + (G - R)) / 6
     elif (G >= B && B >= R)
        I = G
        S = G - R
        F = (4 - (G - B)) / 6
     elif (B >= G && G >= R)
        I = B
        S = B - R
        F = (4 + (B - G)) / 6
     else
        I = B
        S = B - G
        F = (6 + (B - R)) / 6
     fi

 'cielab'
     |X|   |0.476   0.299   0.175|   |R|
     |Y| = |0.262   0.656   0.082| * |G|
     |Z|   |0.020   0.161   0.909|   |B| 

     L = 116 * (Y ^ (1 / 3)) - 16
     a = 500 * (((X / 0.95) ^ (1 / 3)) - (Y ^ (1 / 3)))
     b = 200 * ((Y ^ (1 / 3)) - ((Z / 1.09) ^ (1 / 3)))

 'i1i2i3'
     |I1|   | 0.333 0.333 0.333|   |R|
     |I2| = | 1.0   0.0  -1.0  | * |G|
     |I3|   |-0.5   1.0  -0.5  |   |B|

 'ciexyz2'
     |X|   |0.620   0.170   0.180|   |R|
     |Y| = |0.310   0.590   0.110| * |G|
     |Z|   |0.000   0.066   1.020|   |B|

 'ciexyz3'
     |X|   |0.618   0.177   0.205|   |R|
     |Y| = |0.299   0.587   0.114| * |G|
     |Z|   |0.000   0.056   0.944|   |B|

/* Tranformation from rgb to hsv and conversely */
read_image(Image,"patras") ;
disp_color(Image,WindowHandle) ;
decompose3(Image,&Rimage,&Gimage,&Bimage) ;
trans_from_rgb(Rimage,Gimage,Bimage,&Image1,&Image2,&Image3,"hsv") ;
trans_to_rgb(Image1,Image2,Image3,&ImageRed,&ImageGreen,&ImageBlue,"hsv") ;
compose3(ImageRed,ImageGreen,ImageBlue,&Multichannel) ;
disp_color(Multichannel,WindowHandle);

::trans_from_rgb returns H_MSG_TRUE if all parameters are correct. If the input is empty the behaviour can be set via ::set_system('no_object_result',<Result>). If necessary, an exception handling is raised.

::decompose3

::compose3

::rgb1_to_gray, ::rgb3_to_gray

::trans_to_rgb

Image filters