trans_to_rgbtrans_to_rgbTransToRgbTransToRgb (Operator)

Name

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

Signature

Description

trans_to_rgbtrans_to_rgbTransToRgbTransToRgbTransToRgb transforms an image from an arbitrary color space (ColorSpaceColorSpaceColorSpaceColorSpacecolorSpace) 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_rgbTransToRgbTransToRgbTransToRgb 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_rgbTransFromRgbTransFromRgbTransFromRgb. 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].

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)

'yiq'

Domain:

'yuv'

Domain:

'argyb'

Domain:

'ciexyz'

Domain:

'cielab'

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)

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: (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)

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: (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)

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: (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)

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)

* 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_rgbTransToRgbTransToRgbTransToRgb 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>:)set_system("no_object_result", <Result>)SetSystem("no_object_result", <Result>)SetSystem("no_object_result", <Result>)SetSystem("no_object_result", <Result>). If necessary, an exception is raised.

Possible Predecessors

decompose3decompose3Decompose3Decompose3Decompose3

Possible Successors

compose3compose3Compose3Compose3Compose3, disp_colordisp_colorDispColorDispColorDispColor

Alternatives

linear_trans_colorlinear_trans_colorLinearTransColorLinearTransColorLinearTransColor

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