Default to single-channel output from extractChannel #2658

docs/api-channel.md

@@ -64,13 +64,18 @@ Extract a single channel from a multi-channel image.
 ### Examples
 
 ```javascript
-sharp(input)
+// green.jpg is a greyscale image containing the green channel of the input
+await sharp(input)
   .extractChannel('green')
-  .toColourspace('b-w')
-  .toFile('green.jpg', function(err, info) {
-    // info.channels === 1
-    // green.jpg is a greyscale image containing the green channel of the input
-   });
+  .toFile('green.jpg');
+```
+
+```javascript
+// red1 is the red value of the first pixel, red2 the second pixel etc.
+const [red1, red2, ...] = await sharp(input)
+  .extractChannel(0)
+  .raw()
+  .toBuffer();
 ```
 
 *   Throws **[Error][3]** Invalid channel

docs/api-colour.md

@@ -86,4 +86,4 @@ Returns **Sharp**
 
 [5]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Boolean
 
-[6]: https://github.com/libvips/libvips/blob/master/libvips/iofuncs/enumtypes.c#L568
+[6]: https://github.com/libvips/libvips/blob/3c0bfdf74ce1dc37a6429bed47fa76f16e2cd70a/libvips/iofuncs/enumtypes.c#L777-L794

docs/changelog.md

@@ -17,6 +17,9 @@ Requires libvips v8.11.0
 * Allow multiple platform-arch binaries in same `node_modules` installation tree.
   [#2575](https://github.com/lovell/sharp/issues/2575)
 
+* Default to single-channel `b-w` space when `extractChannel` is used.
+  [#2658](https://github.com/lovell/sharp/issues/2658)
+
 ## v0.28 - *bijou*
 
 Requires libvips v8.10.6