trans_to_rgbtrans_to_rgbTransToRgbTransToRgbtrans_to_rgb (Operator)

Name

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

Signature

Description

trans_to_rgbtrans_to_rgbTransToRgbTransToRgbtrans_to_rgb transforms an image from an arbitrary color space (ColorSpaceColorSpaceColorSpacecolorSpacecolor_space) 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_rgbtrans_to_rgbTransToRgbTransToRgbtrans_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_rgbtrans_from_rgbTransFromRgbTransFromRgbtrans_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'"cielchab""cielchab""cielchab""cielchab" and 'cielchuv'"cielchuv""cielchuv""cielchuv""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'"cielchab""cielchab""cielchab""cielchab" and 'cielchuv'"cielchuv""cielchuv""cielchuv""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].

Supported are the transformations listed below. Note, all domains are based on RGB values scaled to [0; 1]. To obtain the domain of a certain image type, they must be scaled accordingly with the value range. Due to different precision the values obtained using the given equations may slightly differ from the values returned by the operator.

'yiq'

Domain:

'yuv'

Note, this implies that , , and are not independent of each other.

Domain:

'argyb'

Domain:

'ciexyz'

Domain:

'cielab'

Black point B: (, , ) = (0, 0, 0)

White point W (according to image type):

• byte: (, , ) = (255, 255, 255)

• uint2: (, , ) = (, , )

• int4: (, , ) = (, , )

• real: (, , ) = (1.0, 1.0, 1.0)

Domain:

(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.)

'cielchab'

Black point B: (, , ) = (0, 0, 0)

White point W (according to image type):

• byte: (, , ) = (255, 255, 255)

• uint2: (, , ) = (, , )

• int4: (, , ) = (, , )

• real: (, , ) = (1.0, 1.0, 1.0)

Domain:

(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.)

'cieluv'

Black point B: (, , ) = (0, 0, 0)

White point W (according to image type):

• byte: (, , ) = (255, 255, 255)

• uint2: (, , ) = (, , )

• int4: (, , ) = (, , )

• real: (, , ) = (1.0, 1.0, 1.0)

Domain:

(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.)

'cielchuv'

Black point B: (, , ) = (0, 0, 0)

White point W (according to image type):

• byte: (, , ) = (255, 255, 255)

• uint2: (, , ) = (, , )

• int4: (, , ) = (, , )

• real: (, , ) = (1.0, 1.0, 1.0)

Domain:

(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.)

'hls'

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

Domain:

'hsi'

Range of values:

'hsv'

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

Domain:

'ciexyz4'

Domain:

'lms'

Domain:

Attention

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.

Execution Information

• Supports OpenCL compute devices.
• Multithreading type: reentrant (runs in parallel with non-exclusive operators).
• Multithreading scope: global (may be called from any thread).
• Automatically parallelized on tuple level.
• Automatically parallelized on domain level.

Parameters

* 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)

/* Transformation 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);

* 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)

* 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)

Result

trans_to_rgbtrans_to_rgbTransToRgbTransToRgbtrans_to_rgb returns 2 ( H_MSG_TRUE) if all parameters are correct. If the input is empty the behavior can be set via set_system(::'no_object_result', <Result>:)set_system("no_object_result", <Result>)SetSystem("no_object_result", <Result>)SetSystem("no_object_result", <Result>)set_system("no_object_result", <Result>). If necessary, an exception is raised.

Possible Predecessors

decompose3decompose3Decompose3Decompose3decompose3

Possible Successors

compose3compose3Compose3Compose3compose3, disp_colordisp_colorDispColorDispColordisp_color

Alternatives

linear_trans_colorlinear_trans_colorLinearTransColorLinearTransColorlinear_trans_color

See also

decompose3decompose3Decompose3Decompose3decompose3

References

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.

Module

Foundation