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 296 def a(value) 297 value & 0x000000ff 298 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 500 def alpha_decomposable?(color, mask, bg, tolerance = 1) 501 components = decompose_alpha_components(color, mask, bg) 502 sum = components.inject(0) { |a,b| a + b } 503 max = components.max * 3 504 components.max <= 255 && components.min >= 0 && (sum + tolerance * 3) >= max 505 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 288 def b(value) 289 (value & 0x0000ff00) >> 8 290 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 403 def blend(fg, bg) 404 (fg + bg) >> 1 405 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 380 def compose_precise(fg, bg) 381 return fg if opaque?(fg) || fully_transparent?(bg) 382 return bg if fully_transparent?(fg) 383 384 fg_a = a(fg).to_f / MAX 385 bg_a = a(bg).to_f / MAX 386 a_com = (1.0 - fg_a) * bg_a 387 388 new_r = (fg_a * r(fg) + a_com * r(bg)).round 389 new_g = (fg_a * g(fg) + a_com * g(bg)).round 390 new_b = (fg_a * b(fg) + a_com * b(bg)).round 391 new_a = ((fg_a + a_com) * MAX).round 392 rgba(new_r, new_g, new_b, new_a) 393 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 358 def compose_quick(fg, bg) 359 return fg if opaque?(fg) || fully_transparent?(bg) 360 return bg if fully_transparent?(fg) 361 362 a_com = int8_mult(0xff - a(fg), a(bg)) 363 new_r = int8_mult(a(fg), r(fg)) + int8_mult(a_com, r(bg)) 364 new_g = int8_mult(a(fg), g(fg)) + int8_mult(a_com, g(bg)) 365 new_b = int8_mult(a(fg), b(fg)) + int8_mult(a_com, b(bg)) 366 new_a = a(fg) + a_com 367 rgba(new_r, new_g, new_b, new_a) 368 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 521 def decompose_alpha(color, mask, bg) 522 components = decompose_alpha_components(color, mask, bg) 523 (components.inject(0) { |a,b| a + b } / 3.0).round 524 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 534 def decompose_alpha_component(channel, color, mask, bg) 535 cc, mc, bc = send(channel, color), send(channel, mask), send(channel, bg) 536 537 return 0x00 if bc == cc 538 return 0xff if bc == mc 539 return 0xff if cc == mc 540 541 (((bc - cc).to_f / (bc - mc).to_f) * MAX).round 542 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 551 def decompose_alpha_components(color, mask, bg) 552 [ 553 decompose_alpha_component(:r, color, mask, bg), 554 decompose_alpha_component(:g, color, mask, bg), 555 decompose_alpha_component(:b, color, mask, bg) 556 ] 557 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 479 def decompose_color(color, mask, bg, tolerance = 1) 480 if alpha_decomposable?(color, mask, bg, tolerance) 481 mask & 0xffffff00 | decompose_alpha(color, mask, bg) 482 else 483 mask & 0xffffff00 484 end 485 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 716 def euclidean_distance_rgba(pixel_after, pixel_before) 717 return 0.0 if pixel_after == pixel_before 718 719 Math.sqrt( 720 (r(pixel_after) - r(pixel_before))**2 + 721 (g(pixel_after) - g(pixel_before))**2 + 722 (b(pixel_after) - b(pixel_before))**2 + 723 (a(pixel_after) - a(pixel_before))**2 724 ) 725 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 458 def fade(color, factor) 459 new_alpha = int8_mult(a(color), factor) 460 (color & 0xffffff00) | new_alpha 461 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] str The color in hex notation. @return [Integer] The
converted color value.
@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 166 def from_hex(hex_value, opacity = nil) 167 base_color = case hex_value 168 when HEX3_COLOR_REGEXP 169 $1.gsub(/([0-9a-f])/i, '\1\1').hex << 8 170 when HEX6_COLOR_REGEXP 171 $1.hex << 8 172 else 173 raise ArgumentError, "Not a valid hex color notation: #{hex_value.inspect}!" 174 end 175 opacity ||= $2 ? $2.hex : 0xff 176 base_color | opacity 177 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 217 def from_hsl(hue, saturation, lightness, alpha = 255) 218 raise ArgumentError, "Hue #{hue} was not between 0 and 360" unless (0..360).include?(hue) 219 raise ArgumentError, "Saturation #{saturation} was not between 0 and 1" unless (0..1).include?(saturation) 220 raise ArgumentError, "Lightness #{lightness} was not between 0 and 1" unless (0..1).include?(lightness) 221 chroma = (1 - (2 * lightness - 1).abs) * saturation 222 rgb = cylindrical_to_cubic(hue, saturation, lightness, chroma) 223 rgb.map! { |component| ((component + lightness - 0.5 * chroma) * 255).to_i } 224 rgb << alpha 225 self.rgba(*rgb) 226 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 193 def from_hsv(hue, saturation, value, alpha = 255) 194 raise ArgumentError, "Hue must be between 0 and 360" unless (0..360).include?(hue) 195 raise ArgumentError, "Saturation must be between 0 and 1" unless (0..1).include?(saturation) 196 raise ArgumentError, "Value/brightness must be between 0 and 1" unless (0..1).include?(value) 197 chroma = value * saturation 198 rgb = cylindrical_to_cubic(hue, saturation, value, chroma) 199 rgb.map! { |component| ((component + value - chroma) * 255).to_i } 200 rgb << alpha 201 self.rgba(*rgb) 202 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 140 def from_rgb_stream(stream, pos = 0) 141 rgb(*stream.unpack("@#{pos}C3")) 142 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 150 def from_rgba_stream(stream, pos = 0) 151 rgba(*stream.unpack("@#{pos}C4")) 152 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 327 def fully_transparent?(value) 328 a(value) == 0x00000000 329 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 280 def g(value) 281 (value & 0x00ff0000) >> 16 282 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 117 def grayscale(teint) 118 teint << 24 | teint << 16 | teint << 8 | 0xff 119 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 319 def grayscale?(value) 320 r(value) == b(value) && b(value) == g(value) 321 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 126 def grayscale_alpha(teint, a) 127 teint << 24 | teint << 16 | teint << 8 | a 128 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 435 def grayscale_teint(color) 436 (r(color) * 0.3 + g(color) * 0.59 + b(color) * 0.11).round 437 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 903 def html_color(color_name, opacity = nil) 904 if color_name.to_s =~ HTML_COLOR_REGEXP 905 opacity ||= $2 ? ($2.to_f * 255.0).round : 0xff 906 base_color_name = $1.gsub(/[^a-z]+/i, '').downcase.to_sym 907 return PREDEFINED_COLORS[base_color_name] | opacity if PREDEFINED_COLORS.has_key?(base_color_name) 908 end 909 raise ArgumentError, "Unknown color name #{color_name}!" 910 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 344 def int8_mult(a, b) 345 t = a * b + 0x80 346 ((t >> 8) + t) >> 8 347 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) @param [Integer] The interpolated color.
# File lib/chunky_png/color.rb 417 def interpolate_quick(fg, bg, alpha) 418 return fg if alpha >= 255 419 return bg if alpha <= 0 420 421 alpha_com = 255 - alpha 422 423 new_r = int8_mult(alpha, r(fg)) + int8_mult(alpha_com, r(bg)) 424 new_g = int8_mult(alpha, g(fg)) + int8_mult(alpha_com, g(bg)) 425 new_b = int8_mult(alpha, b(fg)) + int8_mult(alpha_com, b(bg)) 426 new_a = int8_mult(alpha, a(fg)) + int8_mult(alpha_com, a(bg)) 427 428 rgba(new_r, new_g, new_b, new_a) 429 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 311 def opaque!(value) 312 value | 0x000000ff 313 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 304 def opaque?(value) 305 a(value) == 0x000000ff 306 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] The color value. @return [Integer] The color value, with the opacity applied if one was
given.
# File lib/chunky_png/color.rb 84 def parse(source) 85 return source if source.kind_of?(Integer) 86 case source.to_s 87 when /^\d+$/; source.to_s.to_i 88 when HEX3_COLOR_REGEXP, HEX6_COLOR_REGEXP; from_hex(source.to_s) 89 when HTML_COLOR_REGEXP; html_color(source.to_s) 90 else raise ArgumentError, "Don't know how to create a color from #{source.inspect}!" 91 end 92 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] width The height of the image pass. @return [Integer] The number of bytes used per scanline in a datastream.
# File lib/chunky_png/color.rb 978 def pass_bytesize(color_mode, depth, width, height) 979 return 0 if width == 0 || height == 0 980 (scanline_bytesize(color_mode, depth, width) + 1) * height 981 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 957 def pixel_bitsize(color_mode, depth = 8) 958 samples_per_pixel(color_mode) * depth 959 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 945 def pixel_bytesize(color_mode, depth = 8) 946 return 1 if depth < 8 947 (pixel_bitsize(color_mode, depth) + 7) >> 3 948 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 272 def r(value) 273 (value & 0xff000000) >> 24 274 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 109 def rgb(r, g, b) 110 r << 24 | g << 16 | b << 8 | 0xff 111 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 100 def rgba(r, g, b, a) 101 r << 24 | g << 16 | b << 8 | a 102 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 928 def samples_per_pixel(color_mode) 929 case color_mode 930 when ChunkyPNG::COLOR_INDEXED; 1 931 when ChunkyPNG::COLOR_TRUECOLOR; 3 932 when ChunkyPNG::COLOR_TRUECOLOR_ALPHA; 4 933 when ChunkyPNG::COLOR_GRAYSCALE; 1 934 when ChunkyPNG::COLOR_GRAYSCALE_ALPHA; 2 935 else raise ChunkyPNG::NotSupported, "Don't know the number of samples for this colormode: #{color_mode}!" 936 end 937 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 967 def scanline_bytesize(color_mode, depth, width) 968 ((pixel_bitsize(color_mode, depth) * width) + 7) >> 3 969 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 450 def to_grayscale(color) 451 grayscale_alpha(grayscale_teint(color), a(color)) 452 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 695 def to_grayscale_alpha_bytes(color) 696 [b(color), a(color)] # assumption r == g == b 697 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 681 def to_grayscale_bytes(color) 682 [b(color)] # assumption r == g == b 683 end
Returns a string representing this color using hex notation (i.e. rrggbbaa).
@param [Integer] value The color to convert. @return [String] The color in hex notation, starting with a pound sign.
# File lib/chunky_png/color.rb 568 def to_hex(color, include_alpha = true) 569 include_alpha ? ('#%08x' % color) : ('#%06x' % [color >> 8]) 570 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
include_alpha=true (0-255)
@see en.wikipedia.org/wiki/HSL_and_HSV
# File lib/chunky_png/color.rb 619 def to_hsl(color, include_alpha = false) 620 hue, chroma, max, min = hue_and_chroma(color) 621 lightness = 0.5 * (max + min) 622 saturation = chroma.zero? ? 0.0 : chroma.fdiv(1 - (2 * lightness - 1).abs) 623 624 include_alpha ? [hue, saturation, lightness, a(color)] : 625 [hue, saturation, lightness] 626 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 591 def to_hsv(color, include_alpha = false) 592 hue, chroma, max, _ = hue_and_chroma(color) 593 value = max 594 saturation = chroma.zero? ? 0.0 : chroma.fdiv(value) 595 596 include_alpha ? [hue, saturation, value, a(color)] : 597 [hue, saturation, value] 598 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 661 def to_truecolor_alpha_bytes(color) 662 [r(color), g(color), b(color), a(color)] 663 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 670 def to_truecolor_bytes(color) 671 [r(color), g(color), b(color)] 672 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 @see www.tomjewett.com/colors/hsb.html @private
# File lib/chunky_png/color.rb 249 def cylindrical_to_cubic(hue, saturation, y_component, chroma) 250 hue_prime = hue.fdiv(60) 251 x = chroma * (1 - (hue_prime % 2 - 1).abs) 252 253 case hue_prime 254 when (0...1); [chroma, x, 0] 255 when (1...2); [x, chroma, 0] 256 when (2...3); [0, chroma, x] 257 when (3...4); [0, x, chroma] 258 when (4...5); [x, 0, chroma] 259 when (5..6); [chroma, 0, x] 260 end 261 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] 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 638 def hue_and_chroma(color) 639 scaled_rgb = to_truecolor_bytes(color) 640 scaled_rgb.map! { |component| component.fdiv(255) } 641 min, max = scaled_rgb.minmax 642 chroma = max - min 643 644 r, g, b = scaled_rgb 645 hue_prime = chroma.zero? ? 0 : case max 646 when r; (g - b).fdiv(chroma) 647 when g; (b - r).fdiv(chroma) + 2 648 when b; (r - g).fdiv(chroma) + 4 649 else 0 650 end 651 hue = 60 * hue_prime 652 653 return hue.round, chroma, max, min 654 end