module ChunkyPNG::Color
The Color
module defines methods for handling colors. Within the ChunkyPNG
library, the concepts of pixels and colors are both used, and they are both represented by a Integer.
Pixels/colors are represented in RGBA components. Each of the four components is stored with a depth of 8 bits (maximum value = 255 = {ChunkyPNG::Color::MAX}). Together, these components are stored in a 4-byte Integer.
A color will always be represented using these 4 components in memory. When the image is encoded, a more suitable representation can be used (e.g. rgb, grayscale, palette-based), for which several conversion methods are provided in this module.
Constants
- BLACK
@return [Integer] Black pixel/color
- HEX3_COLOR_REGEXP
@private @return [Regexp] The regexp to parse 3-digit hex color values.
- HEX6_COLOR_REGEXP
@private @return [Regexp] The regexp to parse 6- and 8-digit hex color values.
- HTML_COLOR_REGEXP
@private @return [Regexp] The regexp to parse named color values.
- MAX
@return [Integer] The maximum value of each color component.
- MAX_EUCLIDEAN_DISTANCE_RGBA
Could be simplified as
MAX
* 2, but this format mirrors the math in {#euclidean_distance_rgba} @return [Float] The maximum Euclidean distance of two RGBA colors.- PREDEFINED_COLORS
@return [Hash<Symbol, Integer>] All the predefined color names in HTML.
- TRANSPARENT
@return [Integer] Fully transparent pixel/color
- WHITE
@return [Integer] White pixel/color
Public Instance Methods
Returns the alpha channel value for the color value.
@param [Integer] value The color value. @return [Integer] A value between 0 and MAX
.
# File lib/chunky_png/color.rb 299 def a(value) 300 value & 0x000000ff 301 end
Checks whether an alpha channel value can successfully be composed given the resulting color, the mask color and a background color, all of which should be opaque.
@param [Integer] color The color that was the result of compositing. @param [Integer] mask The opaque variant of the color that was being
composed
@param [Integer] bg The background color on which the color was composed. @param [Integer] tolerance The decomposition tolerance level, a value
between 0 and 255.
@return [Boolean] True if the alpha component can be decomposed
successfully.
@see decompose_alpha
# File lib/chunky_png/color.rb 503 def alpha_decomposable?(color, mask, bg, tolerance = 1) 504 components = decompose_alpha_components(color, mask, bg) 505 sum = components.inject(0) { |a, b| a + b } 506 max = components.max * 3 507 components.max <= 255 && components.min >= 0 && (sum + tolerance * 3) >= max 508 end
Returns the blue-component from the color value.
@param [Integer] value The color value. @return [Integer] A value between 0 and MAX
.
# File lib/chunky_png/color.rb 291 def b(value) 292 (value & 0x0000ff00) >> 8 293 end
Blends the foreground and background color by taking the average of the components.
@param [Integer] fg The foreground color. @param [Integer] bg The foreground color. @return [Integer] The blended color.
# File lib/chunky_png/color.rb 406 def blend(fg, bg) 407 (fg + bg) >> 1 408 end
Composes two colors with an alpha channel using floating point math.
This method uses more precise floating point math, but this precision is lost when the result is converted back to an integer. Because it is slower than the version based on integer math, that version is preferred.
@param [Integer] fg The foreground color. @param [Integer] bg The background color. @return [Integer] The composited color. @see ChunkyPNG::Color#compose_quick
# File lib/chunky_png/color.rb 383 def compose_precise(fg, bg) 384 return fg if opaque?(fg) || fully_transparent?(bg) 385 return bg if fully_transparent?(fg) 386 387 fg_a = a(fg).to_f / MAX 388 bg_a = a(bg).to_f / MAX 389 a_com = (1.0 - fg_a) * bg_a 390 391 new_r = (fg_a * r(fg) + a_com * r(bg)).round 392 new_g = (fg_a * g(fg) + a_com * g(bg)).round 393 new_b = (fg_a * b(fg) + a_com * b(bg)).round 394 new_a = ((fg_a + a_com) * MAX).round 395 rgba(new_r, new_g, new_b, new_a) 396 end
Composes two colors with an alpha channel using integer math.
This version is faster than the version based on floating point math, so this compositing function is used by default.
@param [Integer] fg The foreground color. @param [Integer] bg The background color. @return [Integer] The composited color. @see ChunkyPNG::Color#compose_precise
# File lib/chunky_png/color.rb 361 def compose_quick(fg, bg) 362 return fg if opaque?(fg) || fully_transparent?(bg) 363 return bg if fully_transparent?(fg) 364 365 a_com = int8_mult(0xff - a(fg), a(bg)) 366 new_r = int8_mult(a(fg), r(fg)) + int8_mult(a_com, r(bg)) 367 new_g = int8_mult(a(fg), g(fg)) + int8_mult(a_com, g(bg)) 368 new_b = int8_mult(a(fg), b(fg)) + int8_mult(a_com, b(bg)) 369 new_a = a(fg) + a_com 370 rgba(new_r, new_g, new_b, new_a) 371 end
Decomposes the alpha channel value given the resulting color, the mask color and a background color, all of which should be opaque.
Make sure to call {#alpha_decomposable?} first to see if the alpha channel value can successfully decomposed with a given tolerance, otherwise the return value of this method is undefined.
@param [Integer] color The color that was the result of compositing. @param [Integer] mask The opaque variant of the color that was being
composed
@param [Integer] bg The background color on which the color was composed. @return [Integer] The best fitting alpha channel, a value between 0 and
255.
@see alpha_decomposable?
# File lib/chunky_png/color.rb 524 def decompose_alpha(color, mask, bg) 525 components = decompose_alpha_components(color, mask, bg) 526 (components.inject(0) { |a, b| a + b } / 3.0).round 527 end
Decomposes an alpha channel for either the r, g or b color channel. @param [:r, :g, :b] channel The channel to decompose the alpha channel
from.
@param [Integer] color The color that was the result of compositing. @param [Integer] mask The opaque variant of the color that was being
composed
@param [Integer] bg The background color on which the color was composed. @return [Integer] The decomposed alpha value for the channel.
# File lib/chunky_png/color.rb 537 def decompose_alpha_component(channel, color, mask, bg) 538 cc, mc, bc = send(channel, color), send(channel, mask), send(channel, bg) 539 540 return 0x00 if bc == cc 541 return 0xff if bc == mc 542 return 0xff if cc == mc 543 544 (((bc - cc).to_f / (bc - mc).to_f) * MAX).round 545 end
Decomposes the alpha channels for the r, g and b color channel. @param [Integer] color The color that was the result of compositing. @param [Integer] mask The opaque variant of the color that was being
composed
@param [Integer] bg The background color on which the color was composed. @return [Array<Integer>] The decomposed alpha values for the r, g and b
channels.
# File lib/chunky_png/color.rb 554 def decompose_alpha_components(color, mask, bg) 555 [ 556 decompose_alpha_component(:r, color, mask, bg), 557 decompose_alpha_component(:g, color, mask, bg), 558 decompose_alpha_component(:b, color, mask, bg), 559 ] 560 end
Decomposes a color, given a color, a mask color and a background color. The returned color will be a variant of the mask color, with the alpha channel set to the best fitting value. This basically is the reverse operation if alpha composition.
If the color cannot be decomposed, this method will return the fully transparent variant of the mask color.
@param [Integer] color The color that was the result of compositing. @param [Integer] mask The opaque variant of the color that was being
composed
@param [Integer] bg The background color on which the color was composed. @param [Integer] tolerance The decomposition tolerance level, a value
between 0 and 255.
@return [Integer] The decomposed color, a variant of the masked color
with the alpha channel set to an appropriate value.
# File lib/chunky_png/color.rb 482 def decompose_color(color, mask, bg, tolerance = 1) 483 if alpha_decomposable?(color, mask, bg, tolerance) 484 mask & 0xffffff00 | decompose_alpha(color, mask, bg) 485 else 486 mask & 0xffffff00 487 end 488 end
Compute the Euclidean distance between 2 colors in RGBA
This method simply takes the Euclidean distance between the RGBA channels of 2 colors, which gives us a measure of how different the two colors are.
Although it would be more perceptually accurate to calculate a proper Delta E in Lab colorspace, this method should serve many use-cases while avoiding the overhead of converting RGBA to Lab.
@param pixel_after [Integer] @param pixel_before [Integer] @return [Float]
# File lib/chunky_png/color.rb 722 def euclidean_distance_rgba(pixel_after, pixel_before) 723 return 0.0 if pixel_after == pixel_before 724 725 Math.sqrt( 726 (r(pixel_after) - r(pixel_before))**2 + 727 (g(pixel_after) - g(pixel_before))**2 + 728 (b(pixel_after) - b(pixel_before))**2 + 729 (a(pixel_after) - a(pixel_before))**2 730 ) 731 end
Lowers the intensity of a color, by lowering its alpha by a given factor. @param [Integer] color The color to adjust. @param [Integer] factor Fade factor as an integer between 0 and 255. @return [Integer] The faded color.
# File lib/chunky_png/color.rb 461 def fade(color, factor) 462 new_alpha = int8_mult(a(color), factor) 463 (color & 0xffffff00) | new_alpha 464 end
Creates a color by converting it from a string in hex notation.
It supports colors with (rrggbbaa) or without (rrggbb) alpha channel as well as the 3-digit short format (rgb
) for those without. Color
strings may include the prefix “0x” or “#”.
@param [String] hex_value The color in hex notation. @param [Integer] opacity The opacity value for the color. Overrides any
opacity value given in the hex value if given.
@return [Integer] The color value. @raise [ArgumentError] if the value given is not a hex color notation.
# File lib/chunky_png/color.rb 167 def from_hex(hex_value, opacity = nil) 168 base_color = case hex_value 169 when HEX3_COLOR_REGEXP 170 $1.gsub(/([0-9a-f])/i, '\1\1').hex << 8 171 when HEX6_COLOR_REGEXP 172 $1.hex << 8 173 else 174 raise ArgumentError, "Not a valid hex color notation: #{hex_value.inspect}!" 175 end 176 opacity ||= $2 ? $2.hex : 0xff 177 base_color | opacity 178 end
Creates a new color from an HSL triple.
This implementation follows the modern convention of 0 degrees hue indicating red.
@param [Fixnum] hue The hue component (0-360) @param [Fixnum] saturation The saturation component (0-1) @param [Fixnum] lightness The lightness component (0-1) @param [Fixnum] alpha Defaults to opaque (255). @return [Integer] The newly constructed color value. @raise [ArgumentError] if the hsl triple is invalid. @see en.wikipedia.org/wiki/HSL_and_HSV
# File lib/chunky_png/color.rb 220 def from_hsl(hue, saturation, lightness, alpha = 255) 221 raise ArgumentError, "Hue #{hue} was not between 0 and 360" unless (0..360).cover?(hue) 222 raise ArgumentError, "Saturation #{saturation} was not between 0 and 1" unless (0..1).cover?(saturation) 223 raise ArgumentError, "Lightness #{lightness} was not between 0 and 1" unless (0..1).cover?(lightness) 224 225 chroma = (1 - (2 * lightness - 1).abs) * saturation 226 rgb = cylindrical_to_cubic(hue, saturation, lightness, chroma) 227 rgb.map! { |component| ((component + lightness - 0.5 * chroma) * 255).to_i } 228 rgb << alpha 229 rgba(*rgb) 230 end
Creates a new color from an HSV triple.
Create a new color using an HSV (sometimes also called HSB) triple. The words ‘value` and `brightness` are used interchangeably and synonymously in descriptions of this colorspace. This implementation follows the modern convention of 0 degrees hue indicating red.
@param [Fixnum] hue The hue component (0-360) @param [Fixnum] saturation The saturation component (0-1) @param [Fixnum] value The value (brightness) component (0-1) @param [Fixnum] alpha Defaults to opaque (255). @return [Integer] The newly constructed color value. @raise [ArgumentError] if the hsv triple is invalid. @see en.wikipedia.org/wiki/HSL_and_HSV
# File lib/chunky_png/color.rb 194 def from_hsv(hue, saturation, value, alpha = 255) 195 raise ArgumentError, "Hue must be between 0 and 360" unless (0..360).cover?(hue) 196 raise ArgumentError, "Saturation must be between 0 and 1" unless (0..1).cover?(saturation) 197 raise ArgumentError, "Value/brightness must be between 0 and 1" unless (0..1).cover?(value) 198 199 chroma = value * saturation 200 rgb = cylindrical_to_cubic(hue, saturation, value, chroma) 201 rgb.map! { |component| ((component + value - chroma) * 255).to_i } 202 rgb << alpha 203 rgba(*rgb) 204 end
Creates a color by unpacking an rgb triple from a string.
@param [String] stream The string to load the color from. It should be
at least 3 + pos bytes long.
@param [Integer] pos The position in the string to load the triple from. @return [Integer] The newly constructed color value.
# File lib/chunky_png/color.rb 142 def from_rgb_stream(stream, pos = 0) 143 rgb(*stream.unpack("@#{pos}C3")) 144 end
Creates a color by unpacking an rgba triple from a string
@param [String] stream The string to load the color from. It should be
at least 4 + pos bytes long.
@param [Integer] pos The position in the string to load the triple from. @return [Integer] The newly constructed color value.
# File lib/chunky_png/color.rb 152 def from_rgba_stream(stream, pos = 0) 153 rgba(*stream.unpack("@#{pos}C4")) 154 end
Returns true if this color is fully transparent.
@param [Integer] value The color to test. @return [true, false] True if the alpha channel equals 0.
# File lib/chunky_png/color.rb 330 def fully_transparent?(value) 331 a(value) == 0x00000000 332 end
Returns the green-component from the color value.
@param [Integer] value The color value. @return [Integer] A value between 0 and MAX
.
# File lib/chunky_png/color.rb 283 def g(value) 284 (value & 0x00ff0000) >> 16 285 end
Creates a new color using a grayscale teint. @param [Integer] teint The grayscale teint (0-255), will be used as r, g,
and b value.
@return [Integer] The newly constructed color value.
# File lib/chunky_png/color.rb 119 def grayscale(teint) 120 teint << 24 | teint << 16 | teint << 8 | 0xff 121 end
Returns true if this color is fully transparent.
@param [Integer] value The color to test. @return [true, false] True if the r, g and b component are equal.
# File lib/chunky_png/color.rb 322 def grayscale?(value) 323 r(value) == b(value) && b(value) == g(value) 324 end
Creates a new color using a grayscale teint and alpha value. @param [Integer] teint The grayscale teint (0-255), will be used as r, g,
and b value.
@param [Integer] a The opacity (0-255) @return [Integer] The newly constructed color value.
# File lib/chunky_png/color.rb 128 def grayscale_alpha(teint, a) 129 teint << 24 | teint << 16 | teint << 8 | a 130 end
Calculates the grayscale teint of an RGB color.
@param [Integer] color The color to convert. @return [Integer] The grayscale teint of the input color, 0-255.
# File lib/chunky_png/color.rb 438 def grayscale_teint(color) 439 (r(color) * 0.3 + g(color) * 0.59 + b(color) * 0.11).round 440 end
Gets a color value based on a HTML color name.
The color name is flexible. E.g. 'yellowgreen'
, 'Yellow green'
, 'YellowGreen'
, 'YELLOW_GREEN'
and :yellow_green
will all return the same color value.
You can include a opacity level in the color name (e.g. 'red @ 0.5'
) or give an explicit opacity value as second argument. If no opacity value is given, the color will be fully opaque.
@param [Symbol, String] color_name The color name. It may include an
opacity specifier like <tt>@ 0.8</tt> to set the color's opacity.
@param [Integer] opacity The opacity value for the color between 0 and
255. Overrides any opacity value given in the color name.
@return [Integer] The color value. @raise [ChunkyPNG::Exception] If the color name was not recognized.
# File lib/chunky_png/color.rb 909 def html_color(color_name, opacity = nil) 910 if color_name.to_s =~ HTML_COLOR_REGEXP 911 opacity ||= $2 ? ($2.to_f * 255.0).round : 0xff 912 base_color_name = $1.gsub(/[^a-z]+/i, "").downcase.to_sym 913 return PREDEFINED_COLORS[base_color_name] | opacity if PREDEFINED_COLORS.key?(base_color_name) 914 end 915 raise ArgumentError, "Unknown color name #{color_name}!" 916 end
Multiplies two fractions using integer math, where the fractions are stored using an integer between 0 and 255. This method is used as a helper method for compositing colors using integer math.
This is a quicker implementation of ((a * b) / 255.0).round.
@param [Integer] a The first fraction. @param [Integer] b The second fraction. @return [Integer] The result of the multiplication.
# File lib/chunky_png/color.rb 347 def int8_mult(a, b) 348 t = a * b + 0x80 349 ((t >> 8) + t) >> 8 350 end
Interpolates the foreground and background colors by the given alpha value. This also blends the alpha channels themselves.
A blending factor of 255 will give entirely the foreground, while a blending factor of 0 will give the background.
@param [Integer] fg The foreground color. @param [Integer] bg The background color. @param [Integer] alpha The blending factor (fixed 8bit) @return [Integer] The interpolated color.
# File lib/chunky_png/color.rb 420 def interpolate_quick(fg, bg, alpha) 421 return fg if alpha >= 255 422 return bg if alpha <= 0 423 424 alpha_com = 255 - alpha 425 426 new_r = int8_mult(alpha, r(fg)) + int8_mult(alpha_com, r(bg)) 427 new_g = int8_mult(alpha, g(fg)) + int8_mult(alpha_com, g(bg)) 428 new_b = int8_mult(alpha, b(fg)) + int8_mult(alpha_com, b(bg)) 429 new_a = int8_mult(alpha, a(fg)) + int8_mult(alpha_com, a(bg)) 430 431 rgba(new_r, new_g, new_b, new_a) 432 end
Returns the opaque value of this color by removing the alpha channel. @param [Integer] value The color to transform. @return [Integer] The opaque color
# File lib/chunky_png/color.rb 314 def opaque!(value) 315 value | 0x000000ff 316 end
Returns true if this color is fully opaque.
@param [Integer] value The color to test. @return [true, false] True if the alpha channel equals MAX
.
# File lib/chunky_png/color.rb 307 def opaque?(value) 308 a(value) == 0x000000ff 309 end
Parses a color value given a numeric or string argument.
It supports color numbers, colors in hex notation and named HTML colors.
@param [Integer, String] source The color value. @return [Integer] The color value, with the opacity applied if one was
given.
# File lib/chunky_png/color.rb 86 def parse(source) 87 return source if source.is_a?(Integer) 88 case source.to_s 89 when /^\d+$/ then source.to_s.to_i 90 when HEX3_COLOR_REGEXP, HEX6_COLOR_REGEXP then from_hex(source.to_s) 91 when HTML_COLOR_REGEXP then html_color(source.to_s) 92 else raise ArgumentError, "Don't know how to create a color from #{source.inspect}!" 93 end 94 end
Returns the number of bytes used for an image pass @param [Integer] color_mode The color mode in which the pixels are
stored.
@param [Integer] depth The color depth of the pixels. @param [Integer] width The width of the image pass. @param [Integer] height The height of the image pass. @return [Integer] The number of bytes used per scanline in a datastream.
# File lib/chunky_png/color.rb 984 def pass_bytesize(color_mode, depth, width, height) 985 return 0 if width == 0 || height == 0 986 (scanline_bytesize(color_mode, depth, width) + 1) * height 987 end
Returns the size in bits of a pixel when it is stored using a given color mode.
@param [Integer] color_mode The color mode in which the pixels are
stored.
@param [Integer] depth The color depth of the pixels. @return [Integer] The number of bytes used per pixel in a datastream.
# File lib/chunky_png/color.rb 963 def pixel_bitsize(color_mode, depth = 8) 964 samples_per_pixel(color_mode) * depth 965 end
Returns the size in bytes of a pixel when it is stored using a given color mode.
@param [Integer] color_mode The color mode in which the pixels are
stored.
@return [Integer] The number of bytes used per pixel in a datastream.
# File lib/chunky_png/color.rb 951 def pixel_bytesize(color_mode, depth = 8) 952 return 1 if depth < 8 953 (pixel_bitsize(color_mode, depth) + 7) >> 3 954 end
Returns the red-component from the color value.
@param [Integer] value The color value. @return [Integer] A value between 0 and MAX
.
# File lib/chunky_png/color.rb 275 def r(value) 276 (value & 0xff000000) >> 24 277 end
Creates a new color using an r, g, b triple. @param [Integer] r The r-component (0-255) @param [Integer] g The g-component (0-255) @param [Integer] b The b-component (0-255) @return [Integer] The newly constructed color value.
# File lib/chunky_png/color.rb 111 def rgb(r, g, b) 112 r << 24 | g << 16 | b << 8 | 0xff 113 end
Creates a new color using an r, g, b triple and an alpha value. @param [Integer] r The r-component (0-255) @param [Integer] g The g-component (0-255) @param [Integer] b The b-component (0-255) @param [Integer] a The opacity (0-255) @return [Integer] The newly constructed color value.
# File lib/chunky_png/color.rb 102 def rgba(r, g, b, a) 103 r << 24 | g << 16 | b << 8 | a 104 end
Returns the number of sample values per pixel. @param [Integer] color_mode The color mode being used. @return [Integer] The number of sample values per pixel.
# File lib/chunky_png/color.rb 934 def samples_per_pixel(color_mode) 935 case color_mode 936 when ChunkyPNG::COLOR_INDEXED then 1 937 when ChunkyPNG::COLOR_TRUECOLOR then 3 938 when ChunkyPNG::COLOR_TRUECOLOR_ALPHA then 4 939 when ChunkyPNG::COLOR_GRAYSCALE then 1 940 when ChunkyPNG::COLOR_GRAYSCALE_ALPHA then 2 941 else raise ChunkyPNG::NotSupported, "Don't know the number of samples for this colormode: #{color_mode}!" 942 end 943 end
Returns the number of bytes used per scanline. @param [Integer] color_mode The color mode in which the pixels are
stored.
@param [Integer] depth The color depth of the pixels. @param [Integer] width The number of pixels per scanline. @return [Integer] The number of bytes used per scanline in a datastream.
# File lib/chunky_png/color.rb 973 def scanline_bytesize(color_mode, depth, width) 974 ((pixel_bitsize(color_mode, depth) * width) + 7) >> 3 975 end
Converts a color to a fiting grayscale value. It will conserve the alpha channel.
This method will return a full color value, with the R, G, and B value set to the grayscale teint calcuated from the input color’s R, G and B values.
@param [Integer] color The color to convert. @return [Integer] The input color, converted to the best fitting
grayscale.
@see grayscale_teint
# File lib/chunky_png/color.rb 453 def to_grayscale(color) 454 grayscale_alpha(grayscale_teint(color), a(color)) 455 end
Returns an array with the grayscale teint and alpha channel values for this color.
This method expects the color to be grayscale, i.e. r, g, and b value to be equal and uses only the B channel. If you need to convert a color to grayscale first, see {#to_grayscale}.
@param [Integer] color The grayscale color to convert. @return [Array<Integer>] An array with 2 Integer elements. @see to_grayscale
# File lib/chunky_png/color.rb 701 def to_grayscale_alpha_bytes(color) 702 [b(color), a(color)] # assumption r == g == b 703 end
Returns an array with the grayscale teint value for this color.
This method expects the r, g, and b value to be equal, and the alpha channel will be discarded.
@param [Integer] color The grayscale color to convert. @return [Array<Integer>] An array with 1 Integer element.
# File lib/chunky_png/color.rb 687 def to_grayscale_bytes(color) 688 [b(color)] # assumption r == g == b 689 end
Returns a string representing this color using hex notation (i.e. rrggbbaa).
@param [Integer] color The color to convert. @param [Boolean] include_alpha @return [String] The color in hex notation, starting with a pound sign.
# File lib/chunky_png/color.rb 572 def to_hex(color, include_alpha = true) 573 include_alpha ? ("#%08x" % color) : ("#%06x" % [color >> 8]) 574 end
Returns an array with the separate HSL components of a color.
Because ChunkyPNG
internally handles colors as Integers for performance reasons, some rounding occurs when importing or exporting HSL colors whose coordinates are float-based. Because of this rounding, to_hsl
and from_hsl
may not be perfect inverses.
This implementation follows the modern convention of 0 degrees hue indicating red.
@param [Integer] color The ChunkyPNG
color to convert. @param [Boolean] include_alpha Flag indicates whether a fourth element
representing alpha channel should be included in the returned array.
@return [Array<Fixnum>] The hue of the color (0-360) @return [Array<Fixnum>] The saturation of the color (0-1) @return [Array<Fixnum>] The lightness of the color (0-1) @return [Array<Fixnum>] Optional fourth element for alpha, included if
include_alpha=true (0-255)
@see en.wikipedia.org/wiki/HSL_and_HSV
# File lib/chunky_png/color.rb 624 def to_hsl(color, include_alpha = false) 625 hue, chroma, max, min = hue_and_chroma(color) 626 lightness = 0.5 * (max + min) 627 saturation = chroma.zero? ? 0.0 : chroma.fdiv(1 - (2 * lightness - 1).abs) 628 629 include_alpha ? [hue, saturation, lightness, a(color)] : 630 [hue, saturation, lightness] 631 end
Returns an array with the separate HSV components of a color.
Because ChunkyPNG
internally handles colors as Integers for performance reasons, some rounding occurs when importing or exporting HSV colors whose coordinates are float-based. Because of this rounding, to_hsv
and from_hsv
may not be perfect inverses.
This implementation follows the modern convention of 0 degrees hue indicating red.
@param [Integer] color The ChunkyPNG
color to convert. @param [Boolean] include_alpha Flag indicates whether a fourth element
representing alpha channel should be included in the returned array.
@return [Array] The hue of the color (0-360) @return [Array] The saturation of the color (0-1) @return [Array] The value of the color (0-1) @return [Array] Optional fourth element for alpha, included if
include_alpha=true (0-255)
@see en.wikipedia.org/wiki/HSL_and_HSV
# File lib/chunky_png/color.rb 595 def to_hsv(color, include_alpha = false) 596 hue, chroma, max, _ = hue_and_chroma(color) 597 value = max 598 saturation = chroma.zero? ? 0.0 : chroma.fdiv(value) 599 600 include_alpha ? [hue, saturation, value, a(color)] : 601 [hue, saturation, value] 602 end
Returns an array with the separate RGBA values for this color.
@param [Integer] color The color to convert. @return [Array<Integer>] An array with 4 Integer elements.
# File lib/chunky_png/color.rb 667 def to_truecolor_alpha_bytes(color) 668 [r(color), g(color), b(color), a(color)] 669 end
Returns an array with the separate RGB values for this color. The alpha channel will be discarded.
@param [Integer] color The color to convert. @return [Array<Integer>] An array with 3 Integer elements.
# File lib/chunky_png/color.rb 676 def to_truecolor_bytes(color) 677 [r(color), g(color), b(color)] 678 end
Private Instance Methods
Convert one HSL or HSV triple and associated chroma to a scaled rgb triple
This method encapsulates the shared mathematical operations needed to convert coordinates from a cylindrical colorspace such as HSL or HSV into coordinates of the RGB colorspace.
Even though chroma values are derived from the other three coordinates, the formula for calculating chroma differs for each colorspace. Since it is calculated differently for each colorspace, it must be passed in as a parameter.
@param [Fixnum] hue The hue-component (0-360) @param [Fixnum] saturation The saturation-component (0-1) @param [Fixnum] y_component The y_component can represent either lightness
or brightness/value (0-1) depending on which scheme (HSV/HSL) is being used.
@param [Fixnum] chroma The associated chroma value. @return [Array<Fixnum>] A scaled r,g,b triple. Scheme-dependent
adjustments are still needed to reach the true r,g,b values.
@see en.wikipedia.org/wiki/HSL_and_HSV @private
# File lib/chunky_png/color.rb 252 def cylindrical_to_cubic(hue, saturation, y_component, chroma) 253 hue_prime = hue.fdiv(60) 254 x = chroma * (1 - (hue_prime % 2 - 1).abs) 255 256 case hue_prime 257 when (0...1) then [chroma, x, 0] 258 when (1...2) then [x, chroma, 0] 259 when (2...3) then [0, chroma, x] 260 when (3...4) then [0, x, chroma] 261 when (4...5) then [x, 0, chroma] 262 when (5..6) then [chroma, 0, x] 263 end 264 end
This method encapsulates the logic needed to extract hue and chroma from a ChunkPNG color. This logic is shared by the cylindrical HSV/HSB and HSL color space models.
@param [Integer] color A ChunkyPNG
color. @return [Fixnum] hue The hue of the color (0-360) @return [Fixnum] chroma The chroma of the color (0-1) @return [Fixnum] max The magnitude of the largest scaled rgb component (0-1) @return [Fixnum] min The magnitude of the smallest scaled rgb component (0-1) @private
# File lib/chunky_png/color.rb 643 def hue_and_chroma(color) 644 scaled_rgb = to_truecolor_bytes(color) 645 scaled_rgb.map! { |component| component.fdiv(255) } 646 min, max = scaled_rgb.minmax 647 chroma = max - min 648 649 r, g, b = scaled_rgb 650 hue_prime = chroma.zero? ? 0 : case max 651 when r then (g - b).fdiv(chroma) 652 when g then (b - r).fdiv(chroma) + 2 653 when b then (r - g).fdiv(chroma) + 4 654 else 0 655 end 656 hue = 60 * hue_prime 657 658 [hue.round, chroma, max, min] 659 end