NAME

hltorgb -- Convert brightness and hue images to red, green, and blue.

USAGE

hltorgb lightness hue saturation rgbroot

DESCRIPTION

Convert a pair of images representing brightness and hue into three images representing red, green, and blue. This task assumes that the images are the same size and registered.

Any range of input brightness and color values can specified and will map to any range of hue and lightness. Ranges are mapped linearly between specified values. If any of the input scaling limits is specified as INDEF, the limit is taken from the data. If an output scaling limit is specified as INDEF, the limit is set to the limit of the natural range of that parameter.

Hue is a circular function whose range is [0:360] in degrees, with zero representing red, traversing through yellow, green, cyan, blue, magenta, and back to red (including all intermediate colors). The range of lightness is [0:1]. Note that the range in output lightness specified by olmin and olmax do not represent the data values in the output red, green, and blue images. Rather they represent the range of the lightness values which map to RGB together with the hue and saturation values. The output RGB image values are always in the range [0:1]. Any input color values outside the specified range should map to INDEF, which means the output color triples will have the same value and represent the scaled gray value of the input intensity image.

This task uses the standard transformation between the Hue, Saturation, and Lightness (HLS) and Red, Green, and Blue (RGB) color systems.

Note that the output image can only be displayed if you are using a "true color" display with appropriate software, i.e., "red" images are mapped only to red phosphors, green to green, and blue to blue. This is different from displaying an image with a frame buffer that supports color maps (look-up tables), although you could convert the three images to a single image using "color quanitization" or "color dithering".

PARAMETERS

lightness = "" [file name]

The input brightness image. This is an image that represents brightness or intensity values in the color representation.

hue = "" [file name]

The input hue image. This is an image that represents the hues or color values in the color representation.

saturation = [real, min=0, max=1]

The constant saturation value in the range [0:1]. The higher the saturation value, the more intense, or bright, the colors. Lower saturation values result in more pastel colors.

rgbroot = "" [file]

The root name of of the red, green and blue output image files. The suffix "_r", "_g", and "_b" will be appended to this root for the three output images. Note that the suffix is applied to the root file name, not the extension, so you may specify any standard IRAF image format extension. For example, if rgbroot = "test.imh", the output files will be named test_r.imh, test_g.imh, and test_b.imh.

(ihmin = INDEF) [real]

The minimum value to scale in the input color image. This will map to the minimum hue value specified by ohmin. If ihmin = INDEF, the minimum input data value is used.

(ihmax = INDEF) [real]

The maximum value to scale in the input color image. This will map to the maximum hue value specified by ohmax. If ihmax = INDEF, the minimum input data value is used.

(ilmin = INDEF) [real]

The minimum value to scale in the input intensity image. This will map to the minimum lightness value specified by olmin. If ilmin = INDEF, the minimum input data value is used.

(ilmax = INDEF) [real]

The maximum value to scale in the input intensity image. This will map to the maximum lightness value specified by olmax. If ilmax = INDEF, the minimum input data value is used.

(ohmin = INDEF) [real]

The hue value that represents the input image pixel value specified in ihmin, the highest input color value. Hue is a circular function whose range is [0:360] in degrees, with zero representing red, traversing through yellow, green, cyan, blue, magenta, and back to red. If 'ohmin = INDEF', the lowest data value in the input file is used.

(ohmax = INDEF) [real]

The hue value that represents the input image pixel value specified in ihmax, the highest input color value. Hue is a circular function whose range is [0:360] in degrees, with zero representing red, traversing through yellow, green, cyan, blue, magenta, and back to red. If 'ohmax = INDEF', the lowest data value in the input file is used.

(olmin = INDEF) [real]

The lightness value that represents the input image pixel value specified in ilmin. Lightness ranges from [0:1]. If olmin = INDEF, the minimum input data value is used. Note that this is not the range in values in the output red, green, and blue images. Those are always in the range [0:1]. Rather this is the minimum lightness value that subsequently maps to RGB together with the hue and saturation.

(olmax = INDEF) [real]

The lightness value that represents the input image pixel value specified in ilmax. If olmax = INDEF, the minimum input data value is used. Note that this is not the range in values in the output red, green, and blue images. Those are always in the range [0:1]. Rather this is the maximum lightness value that subsequently maps to RGB together with the hue and saturation.

EXAMPLES

1. Convert two images representing hue and brightness named hue and light to three images representing red, green, and blue using the maximum saturation:

pl> hltorgb hue light 1 myim

This will result in three images named myim_r, myim_g, myim_b.

BUGS

SEE ALSO

Type "help playpen option=sys" for a higher-level description of the playpen package.