| Operators |
trans_to_rgb — Transform an image from an arbitrary color space to the RGB color space.
trans_to_rgb(ImageInput1, ImageInput2, ImageInput3 : ImageRed, ImageGreen, ImageBlue : ColorSpace : )
trans_to_rgb transforms an image from an arbitrary color space (ColorSpace) to the RGB color space. The three channels of the image are passed as three separate images on input and output.
The operator trans_to_rgb supports the image types byte, uint2, int4, and real. The domain of the input images must match the domain provided by a corresponding transformation with trans_from_rgb. If not, the results of the transformation may not be reasonable.
This includes some scalings in the case of certain image types and transformations:
Considering byte and uint2 images, the domain of color space values is expected to be spread to the full domain of [0..255] or [0..65535], respectively. This includes a shift in the case of signed values, such that the origin of signed values (e.g., CIELab) may not be at the center of the domain.
Hue values are represented by angles of [0..2PI[ and are coded for the particular image types differently:
byte-images map the angle domain on [0..255].
uint2/int4-images are coded in minutes of arc [0..21600[, except for the transformations 'cielchab' and 'cielchuv' for int4-images, where they are coded in seconds of arc [0..1296000[.
real-images are coded in radians [0..2PI[, except for the transformations 'cielchab' and 'cielchuv', where the standards ISO 11664-4:2008 and ISO 11664-5:2009 require the hue to be specified in degrees.
Saturation values are represented by percentages of [0..100] and are coded for the particular image type differently:
byte-images map the saturation values to [0..255].
uint2/int4-images map the saturation values to [0..10000].
real-images map the saturation values to [0..1].
The following transformations are supported:
(All domains are based on RGB values scaled to [0; 1]. To obtain the domains for a certain image type, they must be multiplied with the maximum of the image type, e.g., 255 in the case of a byte image)
Black point B: (Rb, Gb, Bb) = (0, 0, 0)
White point W = (Rw, Gw, Bw), according to image type:
byte:=(255, 255, 255), uint2:=(2^16-1, 2^16-1, 2^16-1),
int4:=(2^31-1, 2^31-1, 2^31-1), real:=(1.0, 1.0, 1.0)
(Scaled to the maximum gray value in the case of byte and uint2. In the case of int4 L and a are scaled to the maximum gray value, b is scaled to the minimum gray value, such that the origin stays at 0.)
Black point B: (Rb, Gb, Bb) = (0, 0, 0)
White point W = (Rw, Gw, Bw), according to image type:
byte:=(255, 255, 255), uint2:=(2^16-1, 2^16-1, 2^16-1),
int4:=(2^31-1, 2^31-1, 2^31-1), real:=(1.0, 1.0, 1.0)
(Scaled to the maximum gray value in the case of byte and uint2. In the case of int4, L and C are scaled to the maximum gray value, while h is given in seconds of arc.)
Black point B: (Rb, Gb, Bb) = (0, 0, 0)
White point W = (Rw, Gw, Bw), according to image type:
byte:=(255, 255, 255), uint2:=(2^16-1, 2^16-1, 2^16-1),
int4:=(2^31-1, 2^31-1, 2^31-1), real:=(1.0, 1.0, 1.0)
(Scaled to the maximum gray value in the case of byte and uint2. In the case of int4 L and u are scaled to the maximum gray value, v is scaled to the minimum gray value, such that the origin stays at 0.)
Black point B: (Rb, Gb, Bb) = (0, 0, 0)
White point W = (Rw, Gw, Bw), according to image type:
byte:=(255, 255, 255), uint2:=(2^16-1, 2^16-1, 2^16-1),
int4:=(2^31-1, 2^31-1, 2^31-1), real:=(1.0, 1.0, 1.0)
(Scaled to the maximum gray value in the case of byte and uint2. In the case of int4, L and C are scaled to the maximum gray value, while h is given in seconds of arc.)
Hi := floor(H/rad(60))
Hf := H/rad(60) - Hi
if (L <= 0.5)
Max := L * (S + 1)
else
Max := L + S - (L * S)
endif
Min := 2 * L - Max
if (S == 0)
R := L
G := L
B := L
else
if (Hi == 0)
R := Max
G := Min + Hf * (Max - Min)
B := Min
elseif (Hi == 1)
R := Min + (1 - Hf) * (Max - Min)
G := Max
B := Min
elseif (Hi == 2)
R := Min
G := Max
B := Min + Hf * (Max - Min)
elseif (Hi == 3)
R := Min
G := Min + (1 - Hf) * (Max - Min)
B := Max
elseif (Hi == 4)
R := Min + Hf * (Max - Min)
G := Min
B := Max
elseif (Hi == 5)
R := Max
G := Min
B := Min + (1 - Hf) * (Max - Min)
endif
endif
if (S == 0)
R := V
G := V
B := V
else
Hi := floor(H/rad(60))
Hf := H/rad(60) - Hi
if (Hi == 0)
R := V
G := V * (1 - (S * (1 - Hf)))
B := V * (1 - S)
elseif (Hi == 1)
R := V * (1 - (S * Hf))
G := V
B := V * (1 - S)
elseif (Hi == 2)
R := V * (1 - S)
G := V
B := V * (1 - (S * (1 - Hf)))
elseif (Hi == 3)
R := V * (1 - S)
G := V * (1 - (S * Hf))
B := V
elseif (Hi == 4)
R := V * (1 - (S * (1 - Hf)))
G := V * (1 - S)
B := V
elseif (Hi == 5)
R := V
G := V * (1 - S)
B := V * (1 - (S * Hf))
endif
endif
As the calculations are made with a different numerical precision, the OpenCL implementation of the cielab transformation for images of type int4 is slightly less accurate than the pure C version.
Input image (channel 1).
Input image (channel 2).
Input image (channel 3).
Red channel.
Green channel.
Blue channel.
Color space of the input image.
Default value: 'hsv'
List of values: 'argyb', 'cielab', 'cielchab', 'cielchuv', 'cieluv', 'ciexyz', 'ciexyz4', 'hls', 'hsi', 'hsv', 'lms', 'yiq', 'yuv'
List of values (for compute devices): 'cielab', 'cielchab', 'cieluv', 'cielchuv', 'hsv', 'hsi'
* Transformation from rgb to hsv and conversely read_image(Image,'patras') dev_display(Image) decompose3(Image, Image1, Image2, Image3) trans_from_rgb(Image1,Image2,Image3,ImageH,ImageS,ImageV,'hsv') trans_to_rgb(ImageH,ImageS,ImageV,ImageR,ImageG,ImageB,'hsv') compose3(ImageR,ImageG,ImageB,Multichannel) dev_display(Multichannel)
trans_to_rgb returns 2 (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 is raised.
ITU-R BT.470-6: “Conventional Television Systems”, 1998.
ISO 11664-4:2008: “Colorimetry --- Part 4: CIE 1976 L*a*b* Colour
space”, 2008.
ISO 11664-5:2009: “Colorimetry --- Part 5: CIE 1976 L*u*v* Colour
space and u',v' uniform chromaticity scale diagram”, 2009.
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