Hue

Hue (clip, float "hue", float "sat", float "intensity", string "channels")

Version 1.0. January 2nd, 2005
Copyright (C) 2005 Wilbert Dijkhof.
contact: wilbertdijkhof at yahoo.com

Description of filter

Hue is a port of Graft's Hue VirtualDub filter [Hue link]. It let's you adjust the hue, saturation and intensity.

Parameters

channels = "RYGCBM"

The selectable color flavors: red (R), yellow (Y), green (G), cyan (C), blue (B), magenta (M) and combinations (GCM, etc.).

hue = 0.0

The hue is the color flavor (restricted here to the ones listed above).

Example:

# should change pixels with red hue into yellows, but it doesn't
Colorbars(300,200).ConvertToRGB32
Hue(hue=60, channels="R")

# should rotate all six hue 60 degrees (thus red into yellow, yellow into green, green into cyan,
# cyan into blue, blue into magenta and magenta into red), but it doesn't
Colorbars(300,200).ConvertToRGB32
Hue(hue=60, channels="RYGCBM")

sat = 1.0

The saturation (sat) is the dominance of the hue in the color. It should be noted that this is NOT the same as the saturation in the HSV color format. Setting the saturation to zero converts the clip to (R,G,B) = (Y,Y,Y) where Y is the luminance (ie Y = 0.3086*R + 0.6094*G + 0.0820*B) of the clip [*]. Setting it to one leaves the clip untouched. For values inside [0,1] it just performs linear interpolation, and for values outside [0,1] it performs linear extrapolation.

Example:

# decreases the red pixels of the clip to match the luminance
Colorbars(300,200).ConvertToRGB32
Hue(sat=0, channels="R")

# doesn't do anything
Colorbars(300,200).ConvertToRGB32
Hue(sat=1, channels="R")

# increases the red pixels of the clip to 255
Colorbars(300,200).ConvertToRGB32
Hue(sat=1.5, channels="R")

A pixel is called red if the hue of a pizel is red. It is defined here as follows:

• Assuming blue is the minimum: around the color wheel we get red, yellow, green. red + green makes yellow. So it is broken up as 1/3, 1/3, 1/3. If g < 2/3 r then the hue of the pixel is red. If r < 2/3 g then the pixel is green. Else it is both, so it is yellow.
• Assuming green is the minimum: around the color wheel we get red, magenta, blue. red + blue makes magenta. So it is broken up as 1/3, 1/3, 1/3. If b < 2/3 r then the hue of the pixel is red. If r < 2/3 b then the pixel is blue. Else it is both, so it is magenta.

The same holds for the hue of the other colors.

intensity = 1.0

The intensity indicates how light or dark a color is. Setting it to zero will decrease the red pixels (if you asked for the red color flavor) to black, and setting it to one will leave the clip untouched. Setting it higher than one will increase the red pixels to white.

[*] Usually the luminance is defined as Y = 0.299*R + 0.587*G + 0.114*B (using Rec.601 coefficients), but according Haeberli the used transformation is better for linear RGB colors.

References

Matrix Operations for Image Processing (by Haeberli): I guess this is the references where the used transformations are coming from.
Graft link: Original VirtualDub version of this plugin.

Version

v1.0, 2nd January 2005

• Initial release.

Limitations

* requires progressive video