[posenet] Update docs. (#459)

Author: annxingyuan

posenet/README.md

@@ -74,7 +74,7 @@ const net = await posenet.load({
 
  * **architecture** - Can be either `MobileNetV1` or `ResNet50`. It determines which PoseNet architecture to load.
 
- * **outputStride** - Can be one of `8`, `16`, `32` (Stride `16`, `32` are supported for the ResNet architecture and stride `8`, `16`, `32` are supported for the MobileNetV1 architecture). It specifies the output stride of the PoseNet model. The smaller the value, the larger the output resolution, and more accurate the model at the cost of speed. Set this to a larger value to increase speed at the cost of accuracy.
+ * **outputStride** - Can be one of `8`, `16`, `32` (Stride `16`, `32` are supported for the ResNet architecture and stride `8`, `16`, `32` are supported for the MobileNetV1 architecture. However if you are using stride `32` you must set the multiplier to `1.0`). It specifies the output stride of the PoseNet model. The smaller the value, the larger the output resolution, and more accurate the model at the cost of speed. Set this to a larger value to increase speed at the cost of accuracy.
 
 * **inputResolution** - A `number` or an `Object` of type `{width: number, height: number}`. Defaults to `257.` It specifies the size the image is resized and padded to before it is fed into the PoseNet model. The larger the value, the more accurate the model at the cost of speed. Set this to a smaller value to increase speed at the cost of accuracy. If a number is provided, the image will be resized and padded to be a square with the same width and height.  If `width` and `height` are provided, the image will be resized and padded to the specified width and height.
 

posenet/src/posenet_model.ts

@@ -153,6 +153,13 @@ function validateModelConfig(config: ModelConfig) {
         `for architecture ${config.architecture}.`);
   }
 
+  if (config.architecture === 'MobileNetV1' && config.outputStride === 32 &&
+      config.multiplier !== 1) {
+    throw new Error(
+        `When using an output stride of 32, ` +
+        `you must select 1 as the multiplier.`);
+  }
+
   return config;
 }