better way to png

juliabrot-zoom.ipynb

@@ -186,7 +186,7 @@
     "# Change some of the preview grid settings, for example size. Fractal will generate below cell\n",
     "#  Max dimensions are 16K x 16K, beware PS memory is limited and large images may have issues when coloring\n",
     "#  Note: cannot override kernel_mode unless overlay is reloaded!\n",
-    "big_grid.set_size(1920,1080)\n",
+    "big_grid.set_size(1920, 1080)\n",
     "big_grid.settings.max_iterations = int(jui.iter_slider.value)\n",
     "big_tile = jui.juliabrot.compute(big_grid.tile_list[0], True)"
    ]
@@ -282,8 +282,15 @@
    "outputs": [],
    "source": [
     "# Create the canvas, push the data to it\n",
-    "canvas_full = jui.Canvas(width=big_tile.sizeX, height=big_tile.sizeY)\n",
-    "canvas_full.sync_image_data = True\n",
+    "canvas_full = jui.Canvas(width=big_tile.sizeX, height=big_tile.sizeY, sync_image_data=True)\n",
+    "def save_canvas_to_file(*args, **kwargs):\n",
+    "    # Uncomment the following line to write image data from canvas to PNG file\n",
+    "    #canvas_full.to_file('./user-images/fractal.png')\n",
+    "    pass\n",
+    "\n",
+    "# Listen to changes on the ``image_data`` trait and call ``save_to_file`` when it changes.\n",
+    "canvas_full.observe(save_canvas_to_file, 'image_data')\n",
+    "\n",
     "with jui.hold_canvas(canvas_full) :\n",
     "    canvas_full.put_image_data(rgb, 0, 0)\n",
     "    canvas_full.fill_style=\"#ffffff\"  # Set text color\n",
@@ -311,16 +318,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Save the above canvas as an 8-bit PNG file, canvas.to_file() can have issues for large 4K sized images, use the 2nd method if it does"
-   ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {},
-   "outputs": [],
-   "source": [
-    "canvas_full.to_file('./user-images/fractal.png')"
+    "Save the above canvas as an 8-bit PNG file, canvas.to_file() can have issues for large 4K sized images"
    ]
   },
   {
@@ -329,9 +327,9 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "# Uncomment alternative and slower method to save to png (but it won't have the text)\n",
-    "#from skimage.io import imsave\n",
-    "#imsave('./user-images/fractal.png', rgb.astype(np.uint8)) # rgb is 64-bit float and scaled for 8-bit color"
+    "# Uncomment alternative and slower method to save to png (but it won't have the ipycanvas text)\n",
+    "from skimage.io import imsave\n",
+    "imsave('./user-images/fractal-sk.png', rgb.astype(np.uint8)) # rgb is 64-bit float and scaled for 8-bit color"
    ]
   },
   {