Module: ChunkyPNG::Color
Overview
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 Fixnum.
Pixels/colors are represented in RGBA componetns. Each of the four components is stored with a depth of 8 bits (maximum value = 255 = MAX). Together, these components are stored in a 4-byte Fixnum.
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.
Constant Summary collapse
- MAX =
The maximum value of each color component.
0xff
- BLACK =
Black pixel/color
rgb( 0, 0, 0)
- WHITE =
White pixel/color
rgb(255, 255, 255)
- TRANSPARENT =
Fully transparent pixel/color
rgba(255, 255, 255, 0)
Instance Method Summary collapse
-
#a(value) ⇒ Fixnum
Returns the alpha channel value for the color value.
-
#alpha_decomposable?(color, mask, bg, tolerance = 1) ⇒ Fixnum
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.
-
#b(value) ⇒ Fixnum
Returns the blue-component from the color value.
-
#blend(fg, bg) ⇒ Fixnum
Blends the foreground and background color by taking the average of the components.
-
#bytesize(color_mode) ⇒ Fixnum
Returns the size in bytes of a pixel when it is stored using a given color mode.
-
#compose_precise(fg, bg) ⇒ Fixnum
Composes two colors with an alpha channel using floating point math.
-
#compose_quick(fg, bg) ⇒ Fixnum
(also: #compose)
Composes two colors with an alpha channel using integer math.
-
#decompose_alpha(color, mask, bg) ⇒ Fixnum
Decomposes the alpha channel value given the resulting color, the mask color and a background color, all of which should be opaque.
-
#decompose_alpha_component(channel, color, mask, bg) ⇒ Object
Decomposes an alpha channel for either the r, g or b color channel.
-
#decompose_alpha_components(color, mask, bg) ⇒ Array<Fixnum>
Decomposes the alpha channels for the r, g and b color channel.
-
#decompose_color(color, mask, bg, tolerance = 1) ⇒ Fixnum
Decomposes a color, given a color, a mask color and a background color.
-
#fade(color, factor) ⇒ Fixnum
Lowers the intensity of a color, by lowering its alpha by a given factor.
-
#from_hex(str) ⇒ Object
Creates a color by converting it from a string in hex notation.
-
#from_rgb_stream(stream, pos = 0) ⇒ Fixnum
Creates a color by unpacking an rgb triple from a string.
-
#from_rgba_stream(stream, pos = 0) ⇒ Fixnum
Creates a color by unpacking an rgba triple from a string.
-
#fully_transparent?(value) ⇒ true, false
Returns true if this color is fully transparent.
-
#g(value) ⇒ Fixnum
Returns the green-component from the color value.
-
#grayscale(teint) ⇒ ChunkyPNG::Color
Creates a new color using a grayscale teint.
-
#grayscale?(value) ⇒ true, false
Returns true if this color is fully transparent.
-
#grayscale_alpha(teint, a) ⇒ Fixnum
Creates a new color using a grayscale teint and alpha value.
-
#int8_mult(a, b) ⇒ Fixnum
Multiplies two fractions using integer math, where the fractions are stored using an integer between 0 and 255.
-
#opaque!(value) ⇒ Fixnum
Returns the opaque value of this color by removing the alpha channel.
-
#opaque?(value) ⇒ true, false
Returns true if this color is fully opaque.
-
#r(value) ⇒ Fixnum
Returns the red-component from the color value.
-
#rgb(r, g, b) ⇒ Fixnum
Creates a new color using an r, g, b triple.
-
#rgba(r, g, b, a) ⇒ Fixnum
Creates a new color using an r, g, b triple and an alpha value.
-
#to_grayscale_alpha_bytes(color) ⇒ Array<Fixnum>
Returns an array with the grayscale teint and alpha channel values for this color.
-
#to_grayscale_bytes(color) ⇒ Array<Fixnum>
Returns an array with the grayscale teint value for this color.
-
#to_hex(color, include_alpha = true) ⇒ String
Returns a string representing this color using hex notation (i.e. #rrggbbaa).
-
#to_truecolor_alpha_bytes(color) ⇒ Array<Fixnum>
Returns an array with the separate RGBA values for this color.
-
#to_truecolor_bytes(color) ⇒ Array<Fixnum>
Returns an array with the separate RGB values for this color.
Instance Method Details
#a(value) ⇒ Fixnum
Returns the alpha channel value for the color value.
121 122 123 |
# File 'lib/chunky_png/color.rb', line 121 def a(value) value & 0x000000ff end |
#alpha_decomposable?(color, mask, bg, tolerance = 1) ⇒ Fixnum
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.
273 274 275 276 277 278 |
# File 'lib/chunky_png/color.rb', line 273 def alpha_decomposable?(color, mask, bg, tolerance = 1) components = decompose_alpha_components(color, mask, bg) sum = components.inject(0) { |a,b| a + b } max = components.max * 3 return components.max <= 255 && components.min >= 0 && (sum + tolerance * 3) >= max end |
#b(value) ⇒ Fixnum
Returns the blue-component from the color value.
113 114 115 |
# File 'lib/chunky_png/color.rb', line 113 def b(value) (value & 0x0000ff00) >> 8 end |
#blend(fg, bg) ⇒ Fixnum
Blends the foreground and background color by taking the average of the components.
228 229 230 |
# File 'lib/chunky_png/color.rb', line 228 def blend(fg, bg) (fg + bg) >> 1 end |
#bytesize(color_mode) ⇒ Fixnum
Returns the size in bytes of a pixel when it is stored using a given color mode.
392 393 394 395 396 397 398 399 400 401 |
# File 'lib/chunky_png/color.rb', line 392 def bytesize(color_mode) case color_mode when ChunkyPNG::COLOR_INDEXED then 1 when ChunkyPNG::COLOR_TRUECOLOR then 3 when ChunkyPNG::COLOR_TRUECOLOR_ALPHA then 4 when ChunkyPNG::COLOR_GRAYSCALE then 1 when ChunkyPNG::COLOR_GRAYSCALE_ALPHA then 2 else raise "Don't know the bytesize of pixels in this colormode: #{color_mode}!" end end |
#compose_precise(fg, bg) ⇒ Fixnum
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.
205 206 207 208 209 210 211 212 213 214 215 216 217 218 |
# File 'lib/chunky_png/color.rb', line 205 def compose_precise(fg, bg) return fg if opaque?(fg) return bg if fully_transparent?(fg) fg_a = a(fg).to_f / MAX bg_a = a(bg).to_f / MAX a_com = (1.0 - fg_a) * bg_a new_r = (fg_a * r(fg) + a_com * r(bg)).round new_g = (fg_a * g(fg) + a_com * g(bg)).round new_b = (fg_a * b(fg) + a_com * b(bg)).round new_a = ((fg_a + a_com) * MAX).round rgba(new_r, new_g, new_b, new_a) end |
#compose_quick(fg, bg) ⇒ Fixnum Also known as: compose
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.
183 184 185 186 187 188 189 190 191 192 193 |
# File 'lib/chunky_png/color.rb', line 183 def compose_quick(fg, bg) return fg if opaque?(fg) return bg if fully_transparent?(fg) a_com = int8_mult(0xff - a(fg), a(bg)) new_r = int8_mult(a(fg), r(fg)) + int8_mult(a_com, r(bg)) new_g = int8_mult(a(fg), g(fg)) + int8_mult(a_com, g(bg)) new_b = int8_mult(a(fg), b(fg)) + int8_mult(a_com, b(bg)) new_a = a(fg) + a_com rgba(new_r, new_g, new_b, new_a) end |
#decompose_alpha(color, mask, bg) ⇒ Fixnum
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.
292 293 294 295 |
# File 'lib/chunky_png/color.rb', line 292 def decompose_alpha(color, mask, bg) components = decompose_alpha_components(color, mask, bg) (components.inject(0) { |a,b| a + b } / 3.0).round end |
#decompose_alpha_component(channel, color, mask, bg) ⇒ Object
Decomposes an alpha channel for either the r, g or b color channel.
303 304 305 306 |
# File 'lib/chunky_png/color.rb', line 303 def decompose_alpha_component(channel, color, mask, bg) ((send(channel, bg) - send(channel, color)).to_f / (send(channel, bg) - send(channel, mask)).to_f * MAX).round end |
#decompose_alpha_components(color, mask, bg) ⇒ Array<Fixnum>
Decomposes the alpha channels for the r, g and b color channel.
313 314 315 316 317 318 319 |
# File 'lib/chunky_png/color.rb', line 313 def decompose_alpha_components(color, mask, bg) [ decompose_alpha_component(:r, color, mask, bg), decompose_alpha_component(:g, color, mask, bg), decompose_alpha_component(:b, color, mask, bg) ] end |
#decompose_color(color, mask, bg, tolerance = 1) ⇒ Fixnum
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 transparentvariant of the mask color.
255 256 257 258 259 260 261 |
# File 'lib/chunky_png/color.rb', line 255 def decompose_color(color, mask, bg, tolerance = 1) if alpha_decomposable?(color, mask, bg, tolerance) mask & 0xffffff00 | decompose_alpha(color, mask, bg) else mask & 0xffffff00 end end |
#fade(color, factor) ⇒ Fixnum
Lowers the intensity of a color, by lowering its alpha by a given factor.
236 237 238 239 |
# File 'lib/chunky_png/color.rb', line 236 def fade(color, factor) new_alpha = int8_mult(a(color), factor) (color & 0xffffff00) | new_alpha end |
#from_hex(str) ⇒ Object
Creates a color by converting it from a string in hex notation.
It supports colors with (#rrggbbaa) or without (#rrggbb) alpha channel. Color strings may include the prefix “0x” or “#”.
converted color value.
81 82 83 84 85 86 87 |
# File 'lib/chunky_png/color.rb', line 81 def from_hex(str) case str when /^(?:#|0x)?([0-9a-f]{6})$/i then ($1.hex << 8) | 0xff when /^(?:#|0x)?([0-9a-f]{8})$/i then $1.hex else raise "Not a valid hex color notation: #{str.inspect}!" end end |
#from_rgb_stream(stream, pos = 0) ⇒ Fixnum
Creates a color by unpacking an rgb triple from a string.
60 61 62 |
# File 'lib/chunky_png/color.rb', line 60 def from_rgb_stream(stream, pos = 0) rgb(*stream.unpack("@#{pos}C3")) end |
#from_rgba_stream(stream, pos = 0) ⇒ Fixnum
Creates a color by unpacking an rgba triple from a string
70 71 72 |
# File 'lib/chunky_png/color.rb', line 70 def from_rgba_stream(stream, pos = 0) rgba(*stream.unpack("@#{pos}C4")) end |
#fully_transparent?(value) ⇒ true, false
Returns true if this color is fully transparent.
152 153 154 |
# File 'lib/chunky_png/color.rb', line 152 def fully_transparent?(value) a(value) == 0x00000000 end |
#g(value) ⇒ Fixnum
Returns the green-component from the color value.
105 106 107 |
# File 'lib/chunky_png/color.rb', line 105 def g(value) (value & 0x00ff0000) >> 16 end |
#grayscale(teint) ⇒ ChunkyPNG::Color
Creates a new color using a grayscale teint.
40 41 42 |
# File 'lib/chunky_png/color.rb', line 40 def grayscale(teint) teint << 24 | teint << 16 | teint << 8 | 0xff end |
#grayscale?(value) ⇒ true, false
Returns true if this color is fully transparent.
144 145 146 |
# File 'lib/chunky_png/color.rb', line 144 def grayscale?(value) r(value) == b(value) && b(value) == g(value) end |
#grayscale_alpha(teint, a) ⇒ Fixnum
Creates a new color using a grayscale teint and alpha value.
46 47 48 |
# File 'lib/chunky_png/color.rb', line 46 def grayscale_alpha(teint, a) teint << 24 | teint << 16 | teint << 8 | a end |
#int8_mult(a, b) ⇒ Fixnum
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.
169 170 171 172 |
# File 'lib/chunky_png/color.rb', line 169 def int8_mult(a, b) t = a * b + 0x80 ((t >> 8) + t) >> 8 end |
#opaque!(value) ⇒ Fixnum
Returns the opaque value of this color by removing the alpha channel.
136 137 138 |
# File 'lib/chunky_png/color.rb', line 136 def opaque!(value) value | 0x000000ff end |
#opaque?(value) ⇒ true, false
Returns true if this color is fully opaque.
129 130 131 |
# File 'lib/chunky_png/color.rb', line 129 def opaque?(value) a(value) == 0x000000ff end |
#r(value) ⇒ Fixnum
Returns the red-component from the color value.
97 98 99 |
# File 'lib/chunky_png/color.rb', line 97 def r(value) (value & 0xff000000) >> 24 end |
#rgb(r, g, b) ⇒ Fixnum
Creates a new color using an r, g, b triple.
34 35 36 |
# File 'lib/chunky_png/color.rb', line 34 def rgb(r, g, b) r << 24 | g << 16 | b << 8 | 0xff end |
#rgba(r, g, b, a) ⇒ Fixnum
Creates a new color using an r, g, b triple and an alpha value.
28 29 30 |
# File 'lib/chunky_png/color.rb', line 28 def rgba(r, g, b, a) r << 24 | g << 16 | b << 8 | a end |
#to_grayscale_alpha_bytes(color) ⇒ Array<Fixnum>
Returns an array with the grayscale teint and alpha channel values for this color.
This method expects the r,g and b value to be equal.
368 369 370 |
# File 'lib/chunky_png/color.rb', line 368 def to_grayscale_alpha_bytes(color) [r(color), a(color)] # assumption r == g == b end |
#to_grayscale_bytes(color) ⇒ Array<Fixnum>
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.
357 358 359 |
# File 'lib/chunky_png/color.rb', line 357 def to_grayscale_bytes(color) [r(color)] # assumption r == g == b end |
#to_hex(color, include_alpha = true) ⇒ String
Returns a string representing this color using hex notation (i.e. #rrggbbaa).
329 330 331 |
# File 'lib/chunky_png/color.rb', line 329 def to_hex(color, include_alpha = true) include_alpha ? ('#%08x' % color) : ('#%06x' % [color >> 8]) end |
#to_truecolor_alpha_bytes(color) ⇒ Array<Fixnum>
Returns an array with the separate RGBA values for this color.
337 338 339 |
# File 'lib/chunky_png/color.rb', line 337 def to_truecolor_alpha_bytes(color) [r(color), g(color), b(color), a(color)] end |
#to_truecolor_bytes(color) ⇒ Array<Fixnum>
Returns an array with the separate RGB values for this color. The alpha channel will be discarded.
346 347 348 |
# File 'lib/chunky_png/color.rb', line 346 def to_truecolor_bytes(color) [r(color), g(color), b(color)] end |