rgb2hsl - Something fun I wrote today

[dylanaraps]

This is very likely not perfect but it seems to pass any RGB color I throw at it.

# rgb2hsl - usage: rgb2hsl r g b

rgb_to_hsl() {
    local r g b
    local h s l
    local min max

    # Ensure input is greater than 0.
    ((r=r < 0 ? 0 : ${1:-0}))
    ((g=g < 0 ? 0 : ${2:-0}))
    ((b=b < 0 ? 0 : ${3:-0}))

    # Ensure input is lesser than 255.
    ((r=r > 255 ? 255 : r))
    ((g=g > 255 ? 255 : g))
    ((b=b > 255 ? 255 : b))

    # Convert RGB value to a 0-100 range.
    #
    # This is usually a 0-1 range but we
    # multiply by 100 to "fake" floating
    # point.
    ((r=r * 100 / 255))
    ((g=g * 100 / 255))
    ((b=b * 100 / 255))

    # Give the min variable the maximum
    # possible value. We must set it to
    # something.
    ((min=255))

    # Find the minimum and maximum RGB
    # values for use below.
    ((min=r < min ? r : min))
    ((max=r > max ? r : max))
    ((min=g < min ? g : min))
    ((max=g > max ? g : max))
    ((min=b < min ? b : min))
    ((max=b > max ? b : max))

    # Calculate the luminace using the
    # above values.
    ((l=(min + max) / 2))

    # Calculate the saturation using a
    # different formula based on its
    # value.
    #
    # Again, we multiply the values by
    # 100 to "fake" floating points.
    ((s=min == max
        ? 0
        : l < 50
            ? (max - min) * 100 / (max + min)
            : (max - min) * 100 / (200 - max - min)
    ))

    # Calculate the hue based on which
    # RGB value is the maximum.
    ((h=s == 0 ? 0
        : r == max
            ? (g - b) * 100 / (max - min)
        : g == max
            ? 200 + (b - r) * 100 / (max - min)
        : b == max
            ? 400 + (r - g) * 100 / (max - min)
        : 0
    ))

    # Convert the calculation result into
    # degrees. Divide by 100 to reverse the
    # floating point hacks.
    ((h=h * 60 / 100))

    printf '%s\n' "$h $s $l"
}

rgb_to_hsl 18 233 45

[georgalis]

excellent! color transformations are challenging! here is the best info I have on wavelength to rgb conversion http://www.physics.sfasu.edu/astro/color/spectra.html https://www.noah.org/wiki/Wavelength_to_RGB_in_Python if you search for "wl_to_rgb.py" you'll find repositories with more color libraries... the function I use accepts a numerator and denominator, calculates a value between 0 and 1 and transformers it to nm, then to rgb hex color. (half bash, half python) being able to transform saturation and brightness on a given hue, would be fantastic everyday!

…

On Tue, Oct 1, 2019 at 8:12 AM dylan ***@***.***> wrote: This is very likely not perfect but it seems to pass any RGB color I throw at it. # rgb2hsl - usage: rgb2hsl r g b rgb_to_hsl() { local r g b local h s l local min max # Ensure input is greater than 0. ((r=r < 0 ? 0 : ${1:-0})) ((g=g < 0 ? 0 : ${2:-0})) ((b=b < 0 ? 0 : ${3:-0})) # Ensure input is lesser than 255. ((r=r > 255 ? 255 : r)) ((g=g > 255 ? 255 : g)) ((b=b > 255 ? 255 : b)) # Convert RGB value to a 0-100 range. # # This is usually a 0-1 range but we # multiply by 100 to "fake" floating # point. ((r=r * 100 / 255)) ((g=g * 100 / 255)) ((b=b * 100 / 255)) # Give the min variable the maximum # possible value. We must set it to # something. ((min=255)) # Find the minimum and maximum RGB # values for use below. ((min=r < min ? r : min)) ((max=r > max ? r : max)) ((min=g < min ? g : min)) ((max=g > max ? g : max)) ((min=b < min ? b : min)) ((max=b > max ? b : max)) # Calculate the luminace using the # above values. ((l=(min + max) / 2)) # Calculate the saturation using a # different formula based on its # value. # # Again, we multiply the values by # 100 to "fake" floating points. ((s=min == max ? 0 : l < 50 ? (max - min) * 100 / (max + min) : (max - min) * 100 / (200 - max - min) )) # Calculate the hue based on which # RGB value is the maximum. ((h=s == 0 ? 0 : r == max ? (g - b) * 100 / (max - min) : g == max ? 200 + (b - r) * 100 / (max - min) : b == max ? 400 + (r - g) * 100 / (max - min) : 0 )) # Convert the calculation result into # degrees. Divide by 100 to reverse the # floating point hacks. ((h=h * 60 / 100)) printf '%s\n' "$h $s $l" } rgb_to_hsl 18 233 45 — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub, or mute the thread.

-- George Georgalis, (415) 894-2710, http://www.galis.org/

[dylanaraps]

Bonus!

The entire function inside an arithmetic block (( )). This really starts to look like another language entirely!

The coolest part:

-> time rgb2hsl
186 100 53
real    0m 0.00s
user    0m 0.00s
sys     0m 0.00s

rgb_to_hsl() ((
    r = r < 0 ? 0 : ${1:-0},
    g = g < 0 ? 0 : ${2:-0},
    b = b < 0 ? 0 : ${3:-0},

    r = r > 255 ? 255 : r,
    g = g > 255 ? 255 : g,
    b = b > 255 ? 255 : b,

    r = r * 100 / 255,
    g = g * 100 / 255,
    b = b * 100 / 255,

    min=255,

    min = r < min ? r : min,
    max = r > max ? r : max,
    min = g < min ? g : min,
    max = g > max ? g : max,
    min = b < min ? b : min,
    max = b > max ? b : max,

    mid = max - min,
    tot = max + min,

    l = tot / 2,

    s = min == max ? 0
        : l < 50
            ? mid * 100 / tot
            : mid * 100 / (200 - max - min),

    h = s == 0 ? 0
        : r == max
            ? (g - b) * 100 / mid
        : g == max
            ? 200 + (b - r) * 100 / mid
        : b == max
            ? 400 + (r - g) * 100 / mid
        : 0,

    h = h * 60 / 100
))

rgb_to_hsl 18 233 255
printf '%s\n' "$h $s $l"

[ogdenjosh]

It seems to be failing with "#944B53" (148, 75, 83).
Looks like this is due to g < b when r == max, since the calculation for h will give us a negative value in this scenario.

EDIT: This seems to work as far as I've tested

    # Calculate the hue based on which
    # RGB value is the maximum.
    ((h=s == 0 ? 0
        : r == max
            ? (g - b) * 100 / (max - min)
        : g == max
            ? 200 + (b - r) * 100 / (max - min)
        : b == max
            ? 400 + (r - g) * 100 / (max - min)
        : 0
    ))

    # If hue is negative, add 600.
    ((h=h < 0 ? 600 + h : h))

    # Convert the calculation result into
    # degrees. Divide by 100 to reverse the
    # floating point hacks.
    ((h=h * 60 / 100))