mvp

.gitignore

@@ -102,3 +102,7 @@ dist
 
 # TernJS port file
 .tern-port
+
+*.tif
+*.tiff
+test/data/*.json

README.md

@@ -1,2 +1,36 @@
 # geotiff-palette
 Get the Palette (aka Color Map) for a GeoTIFF
+
+# install
+```bash
+npm install geotiff-palette
+```
+
+# usage
+## downloaded GeoTIFF
+```
+const { readFileSync } = require('fs');
+const { fromArrayBuffer } = require('geotiff');
+const { getPalette } = require('geotiff-palette');
+
+const data = readFileSync('image.tif');
+const arrayBuffer = data.buffer.slice(data.byteOffset, data.byteOffset + data.byteLength);
+const geotiff = await fromArrayBuffer(arrayBuffer);
+const image = await geotiff.getImage();
+const palette = await getPalette(image);
+console.log(palette);
+```
+palette will look something like this:
+```
+[
+  [ 112, 108, 96, 255 ],  [ 112, 104, 80, 255 ],  [ 104, 104, 104, 255 ],
+  [ 96, 88, 52, 255 ],    [ 104, 104, 112, 255 ], [ 128, 120, 108, 255 ],
+  [ 160, 160, 160, 255 ], [ 152, 152, 144, 255 ], [ 104, 96, 72, 255 ],
+  [ 96, 80, 44, 255 ],    [ 40, 48, 56, 255 ],    [ 152, 144, 144, 255 ],
+  [ 32, 48, 56, 255 ],    [ 120, 120, 96, 255 ],  [ 112, 120, 104, 255 ],
+  ... 256 total items
+]
+```
+
+# support
+Post an issue at https://github.com/GeoTIFF/geotiff-palette or email the package author at daniel.j.dufour@gmail.com

index.js

@@ -0,0 +1,46 @@
+const getPalette = (image, { debug = false } = { debug: false }) => {
+    if (debug) console.log("starting getPalette with image", image);
+    const { fileDirectory } = image;
+    const {
+        BitsPerSample,
+        ColorMap,
+        ImageLength,
+        ImageWidth,
+        PhotometricInterpretation,
+        SampleFormat,
+        SamplesPerPixel
+    } = fileDirectory;
+
+    if (!ColorMap) {
+        throw new Error("[geotiff-palette]: the image does not contain a color map, so we can't make a palette.");
+    }
+
+    const count = Math.pow(2, BitsPerSample);
+    if (debug) console.log("[geotiff-palette]: count:", count);
+
+    const bandSize = ColorMap.length / 3;
+    if (debug) console.log("[geotiff-palette]: bandSize:", bandSize);
+
+    if (bandSize !== count) {
+        throw new Error("[geotiff-palette]: can't handle situations where the color map has more or less values than the number of possible values in a raster");
+    }
+
+    const greenOffset = bandSize;
+    const redOffset = greenOffset + bandSize;
+
+    const result = [];
+    for (let i = 0; i < count; i++) {
+        // colorMap[mapIndex] / 65536 * 256 equals colorMap[mapIndex] / 256
+        // because (1 / 2^16) * (2^8) equals 1 / 2^8
+        result.push([
+            Math.floor(ColorMap[i] / 256), // red
+            Math.floor(ColorMap[greenOffset + i] / 256), // green
+            Math.floor(ColorMap[redOffset + i] / 256), // blue
+            255 // alpha value is always 255
+        ]);
+    }
+    if (debug) console.log("[geotiff-palette]: result is ", result);
+    return result;
+}
+
+module.exports = { getPalette };