fix YV12 documentation

Change-Id: I9a2022101930721a3b3bacc95b02ca21d05f21bb
diff --git a/graphics/java/android/graphics/ImageFormat.java b/graphics/java/android/graphics/ImageFormat.java
index 39a3b05..b8e9384 100644
--- a/graphics/java/android/graphics/ImageFormat.java
+++ b/graphics/java/android/graphics/ImageFormat.java
@@ -31,15 +31,25 @@
     public static final int RGB_565 = 4;
 
     /**
-     * Planar 4:2:0 YCrCb format. This format assumes an horizontal stride of 16
-     * pixels for all planes and an implicit vertical stride of the image
-     * height's next multiple of two.
-     *   y_size = stride * ALIGN(height, 2)
-     *   c_size = ALIGN(stride/2, 16) * height
+     * Android YUV format:
+     *
+     * This format is exposed to software decoders and applications.
+     *
+     * YV12 is a 4:2:0 YCrCb planar format comprised of a WxH Y plane followed
+     * by (W/2) x (H/2) Cr and Cb planes.
+     *
+     * This format assumes
+     * - an even width
+     * - an even height
+     * - a horizontal stride multiple of 16 pixels
+     * - a vertical stride equal to the height
+     *
+     *   y_size = stride * height
+     *   c_size = ALIGN(stride/2, 16) * height/2
      *   size = y_size + c_size * 2
      *   cr_offset = y_size
      *   cb_offset = y_size + c_size
-     * 
+     *
      * Whether this format is supported by the camera hardware can be determined
      * by
      * {@link android.hardware.Camera.Parameters#getSupportedPreviewFormats()}.