MaskHS

MaskHS(clip [, int startHue, int endHue, int maxSat, int minSat, bool coring ] )

int  startHue = 0

int  endHue = 360

The resulting mask will contain source values in the range [startHue, endHue] when startHue<endHue. Note that the hue is periodic, thus a hue of 360 degrees corresponds with a hue of zero degrees.

If endHue<startHue then the range [endHue, 360] and [0, startHue] will be selected (thus anti-clockwise). If you need to select a range of [350, 370] for example, you need to specify startHue=370, endHue=350.

Range 0 to 360 (degrees), default 0, 360; thus when using the default values all pixels will be processed.

As a guide, the following table shows approximate values for the basic colors:

Color	startHue	endHue
Red	075	115
Yellow	150	172
Green	191	258
Cyan	279	300
Blue	316	004
Magenta	028	052

int  maxSat = 150

int  minSat = 0

The resulting mask will contain source values in the range [minSat, maxSat].

Practically the saturation of a pixel will be in the range [0,100] (thus 0-100%), since these correspond to valid RGB pixels (100% corresponds to R=255, G=B=0, which has a saturation of 119). An overshoot (up to 150%) is allowed for non-valid RGB pixels (150% corresponds to U=V=255, which has a saturation of sqrt(127²+127²) = 180).

Range 0 to 150 (percent), default 150, 0; thus when using the default values all pixels will be processed.

bool  coring = true

When set to true, the luma (Y) is clipped to [16,235]; when set to false, the luma is left untouched.

• Suppose we want to create a mask of the skin of the girl below. The proper way to do this is to look at the vectorscope of Histogram:

clip = ... Histogram(clip, mode="color2")

and estimate the hue range you want to select. As can be seen, the orange hue is between (about) 105 and 165 degrees.

Note: axis labels have been added to the vectorscope as a guide – they are not generated by the above script

Start with a wide hue range and narrow it until the output of MaskHS isolates the range of interest. You can also use Tweak to preview the affected range (with sat=0), as the arguments are compatible.

In our example we arrive at startHue=105, endHue=138, and the following mask is obtained:

clip = ... MaskHS(startHue=105, endHue=138)

• Looking at the blue screen example in Overlay the following can be used

testcard = ColorBars

# example subtitle file with blue background:
subs = ImageSource("F:\TestClips\blue.jpg").ConvertToYV24

# subs.Histogram(mode="color2").ConvertToRGB # blue in [345,359]
mask_hs = subs.MaskHS(startHue=340, endHue=359).Levels(0, 1, 255, 255, 0)

Overlay(testcard, subs, mask=mask_hs, mode="blend", opacity=1)