Implemented STD Gamma II interpolator

README.md

@@ -233,6 +233,12 @@ Given a number *t* in the range [0,1], returns the corresponding color from the
 
 Sequential, multi-hue color schemes are available as continuous interpolators (often used with [d3.scaleSequential](https://github.com/d3/d3-scale/blob/master/README.md#sequential-scales)) and as discrete schemes (often used with [d3.scaleOrdinal](https://github.com/d3/d3-scale/blob/master/README.md#ordinal-scales)). Each discrete scheme, such as [d3.schemeBuGn](#schemeBuGn), is represented as an array of arrays of hexadecimal color strings. The *k*th element of this array contains the color scheme of size *k*; for example, `d3.schemeBuGn[9]` contains an array of nine strings representing the nine colors of the blue-green sequential color scheme. Sequential, multi-hue color schemes support a size *k* ranging from 3 to 9.
 
+<a name="interpolateStdGammaII" href="#interpolateStdGammaII">#</a> d3.<b>interpolateStdGammaII</b>(<i>t</i>) [<>](https://github.com/d3/d3-scale-chromatic/blob/master/src/sequential-multi/stdGammaII.js "Source")
+
+<img src="https://raw.githubusercontent.com/d3/d3-scale-chromatic/master/img/StdGammaII.png" width="100%" height="40" alt="StdGammaII">
+
+Given a number *t* in the range [0,1], returns the corresponding color from the “STD GAMMA-II” color scheme initially implemented in [IDL](https://www.l3harrisgeospatial.com/docs/loadingdefaultcolortables.html).
+
 <a name="interpolateTurbo" href="#interpolateTurbo">#</a> d3.<b>interpolateTurbo</b>(<i>t</i>) [<>](https://github.com/d3/d3-scale-chromatic/blob/master/src/sequential-multi/turbo.js "Source")
 
 <img src="https://raw.githubusercontent.com/d3/d3-scale-chromatic/master/img/turbo.png" width="100%" height="40" alt="turbo">

package.json

@@ -37,7 +37,8 @@
   },
   "dependencies": {
     "d3-color": "1 - 2",
-    "d3-interpolate": "1 - 2"
+    "d3-interpolate": "1 - 2",
+    "d3-scale": "3"
   },
   "devDependencies": {
     "eslint": "6",

src/index.js

@@ -39,5 +39,6 @@ export {default as interpolateCividis} from "./sequential-multi/cividis.js";
 export {default as interpolateCubehelixDefault} from "./sequential-multi/cubehelix.js";
 export {default as interpolateRainbow, warm as interpolateWarm, cool as interpolateCool} from "./sequential-multi/rainbow.js";
 export {default as interpolateSinebow} from "./sequential-multi/sinebow.js";
+export {default as interpolateStdGammaII} from "./sequential-multi/stdGammaII.js";
 export {default as interpolateTurbo} from "./sequential-multi/turbo.js";
 export {default as interpolateViridis, magma as interpolateMagma, inferno as interpolateInferno, plasma as interpolatePlasma} from "./sequential-multi/viridis.js";

src/sequential-multi/stdGammaII.js

@@ -0,0 +1,16 @@
+
+import {rgb} from "d3-color";
+import {scaleLinear} from "d3-scale";
+
+// Reimplementation of the IDL "STD Gamma II" color scale, based on bioRad's implementation (https://github.com/adokter/bioRad/blob/e0ede427eb34007dc9985302d40cbdab158e0636/R/color_scale.R#L65-L85)
+// and the explanations at: https://github.com/inbo/crow/issues/38 
+export default function(t) {
+    t = 255 - (t * 255); // Constants below are taken from bioRad and have a 0-255 range
+
+    return rgb(
+        scaleLinear().domain([0, 62, 81, 93, 145, 176, 191, 208, 255]).range([255, 255, 163, 255, 255, 81, 81, 0, 0])(t), 
+        scaleLinear().domain([0, 64, 79, 110, 142, 255]).range([255, 255, 163, 163, 0, 0])(t), 
+        scaleLinear().domain([0, 79, 96, 110, 127, 159, 206, 255]).range([255, 0, 0, 82, 0, 0, 255, 0])(t), 
+        1
+    )
+  }

test/index-test.js

@@ -34,6 +34,7 @@ tape("exports the expected schemes", function(test) {
     "interpolateReds",
     "interpolateSinebow",
     "interpolateSpectral",
+    "interpolateStdGammaII",
     "interpolateTurbo",
     "interpolateViridis",
     "interpolateWarm",

yarn.lock

@@ -169,18 +169,55 @@ cross-spawn@^6.0.5:
     shebang-command "^1.2.0"
     which "^1.2.9"
 
+d3-array@2, d3-array@^2.3.0:
+  version "2.12.1"
+  resolved "https://registry.yarnpkg.com/d3-array/-/d3-array-2.12.1.tgz#e20b41aafcdffdf5d50928004ececf815a465e81"
+  integrity sha512-B0ErZK/66mHtEsR1TkPEEkwdy+WDesimkM5gpZr5Dsg54BiTA5RXtYW5qTLIAcekaS9xfZrzBLF/OAkB3Qn1YQ==
+  dependencies:
+    internmap "^1.0.0"
+
 "d3-color@1 - 2":
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/d3-color/-/d3-color-2.0.0.tgz#8d625cab42ed9b8f601a1760a389f7ea9189d62e"
   integrity sha512-SPXi0TSKPD4g9tw0NMZFnR95XVgUZiBH+uUTqQuDu1OsE2zomHU7ho0FISciaPvosimixwHFl3WHLGabv6dDgQ==
 
-"d3-interpolate@1 - 2":
+"d3-format@1 - 2":
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/d3-format/-/d3-format-2.0.0.tgz#a10bcc0f986c372b729ba447382413aabf5b0767"
+  integrity sha512-Ab3S6XuE/Q+flY96HXT0jOXcM4EAClYFnRGY5zsjRGNy6qCYrQsMffs7cV5Q9xejb35zxW5hf/guKw34kvIKsA==
+
+"d3-interpolate@1 - 2", "[email protected] - 2":
   version "2.0.1"
   resolved "https://registry.yarnpkg.com/d3-interpolate/-/d3-interpolate-2.0.1.tgz#98be499cfb8a3b94d4ff616900501a64abc91163"
   integrity sha512-c5UhwwTs/yybcmTpAVqwSFl6vrQ8JZJoT5F7xNFK9pymv5C0Ymcc9/LIJHtYIggg/yS9YHw8i8O8tgb9pupjeQ==
   dependencies:
     d3-color "1 - 2"
 
+d3-scale@3:
+  version "3.3.0"
+  resolved "https://registry.yarnpkg.com/d3-scale/-/d3-scale-3.3.0.tgz#28c600b29f47e5b9cd2df9749c206727966203f3"
+  integrity sha512-1JGp44NQCt5d1g+Yy+GeOnZP7xHo0ii8zsQp6PGzd+C1/dl0KGsp9A7Mxwp+1D1o4unbTTxVdU/ZOIEBoeZPbQ==
+  dependencies:
+    d3-array "^2.3.0"
+    d3-format "1 - 2"
+    d3-interpolate "1.2.0 - 2"
+    d3-time "^2.1.1"
+    d3-time-format "2 - 3"
+
+"d3-time-format@2 - 3":
+  version "3.0.0"
+  resolved "https://registry.yarnpkg.com/d3-time-format/-/d3-time-format-3.0.0.tgz#df8056c83659e01f20ac5da5fdeae7c08d5f1bb6"
+  integrity sha512-UXJh6EKsHBTjopVqZBhFysQcoXSv/5yLONZvkQ5Kk3qbwiUYkdX17Xa1PT6U1ZWXGGfB1ey5L8dKMlFq2DO0Ag==
+  dependencies:
+    d3-time "1 - 2"
+
+"d3-time@1 - 2", d3-time@^2.1.1:
+  version "2.1.1"
+  resolved "https://registry.yarnpkg.com/d3-time/-/d3-time-2.1.1.tgz#e9d8a8a88691f4548e68ca085e5ff956724a6682"
+  integrity sha512-/eIQe/eR4kCQwq7yxi7z4c6qEXf2IYGcjoWB5OOQy4Tq9Uv39/947qlDcN2TLkiTzQWzvnsuYPB9TrWaNfipKQ==
+  dependencies:
+    d3-array "2"
+
 debug@^4.0.1:
   version "4.1.1"
   resolved "https://registry.yarnpkg.com/debug/-/debug-4.1.1.tgz#3b72260255109c6b589cee050f1d516139664791"
@@ -526,6 +563,11 @@ inquirer@^6.4.1:
     strip-ansi "^5.1.0"
     through "^2.3.6"
 
+internmap@^1.0.0:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/internmap/-/internmap-1.0.1.tgz#0017cc8a3b99605f0302f2b198d272e015e5df95"
+  integrity sha512-lDB5YccMydFBtasVtxnZ3MRBHuaoE8GKsppq+EchKL2U4nK/DmEpPHNH8MZe5HkMtpSiTSOZwfN0tzYjO/lJEw==
+
 is-callable@^1.1.3, is-callable@^1.1.4:
   version "1.1.4"
   resolved "https://registry.yarnpkg.com/is-callable/-/is-callable-1.1.4.tgz#1e1adf219e1eeb684d691f9d6a05ff0d30a24d75"