The getAnnotation() method returns an entirely black png file

[maephisto]

I clone the repo and ranned the example in Firefox, but when exporting the base64 annotation, i can only see a black image. This also happens in the online demo.

Here's an example od the exported data:
data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAcIAAAJYCAYAAADxDeb9AAANvElEQVR4nO3X0Y5TRxRFQfP/H528IATMjLHh2ut0dz2UBIFEC7dztrjdbrf/AOBgeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAE/4NqABNpMHAA/6dvs4hN8+8Tf/fv1ng1AeANzx1dB99s/vjeGffv+z/z3YSB4A/OZfR+tV6s8FXiQPAL6rh84Qcqg8AI5XD5xB5HB5ABytHrV/GUOjyCbyADhWPWb+hgi3/24DAuBI9XgZQvghD4Aj1eNlCOGHPACOUw+XMYRf5AFwlHqwjCF8kAfAUeqxMoTwQR4AR6hHyhjCl/IAOEI9UMYQvpQHwPbqYTKCcFceANurx8kIwl15AGyvHihjCHflAbC9epwMIdyVB8D26nEyhHBXHgBbq4fJGMIf5QGwtXqUDCH8UR4A26oHyRDCQ/IA2FY9SIYQHpIHwLbqQTKE8JA8ALZUj1Gt/vzhCXkAbKceoQnqN4An5AGwlXqApqjfAZ6QB8BW6gGapH4LeFAeANuoh2ea+j3gQXkAbKMenmnq94AH5QGwjXp4JqrfBB6QB8AW6sGZqn4XeEAeAMurx2ay+m3gAXkALK8em8nqt4EH5AGwtHpoVlC/EfxBHgBLq0dmFfU7wR15ACyrHpeV1G8Fd+QBsKR6WFZUvxl8IQ+AJdWjsqL6zeALeQAspx6UVdXvBl/IA2A59aCsqn43+EIeAMupB2Vl9dvBJ/IAWEo9JKur3w8+kQfAUuoh2UH9hvCbPACWUo/IDuo3hN/kAbCMekB2Ur8l/CQPgGXU47GT+i3hJ3kALKMej93U7wnf5QGwjHo4dlW/K8fLA2AJ9VjsrH5bjpcHwBLqsdhZ/bYcLw+AJdRjsbP6bTleHgBLqMdiZ/Xbcrw8AMarh2J39ftyvDwAxquH4gT1G3O0PADGq0fiBPUbc7Q8AMarR+IE9RtztDwAxqtH4gT1G3O0PABGqwfiFPU7c7Q8AEarB+IU9TtztDwARqsH4hT1O3O0PADGq0fiBPUbc7Q8AMarR2J39ftyvDwAxquHYnf1+3K8PADGq4diV/W7wnd5AIxXD8bO6reF24AAGKseiRPUbwy3AQEwVj0SJ6jfGG4DAmCseiROUL8x3AYEwHj1WOyufl+OlwfASL8f6Hosdla/NcfLA2CUrw51PRa7q9+do+UBMEY9Bqer359j5QEwRj0E9N8BjpQHwBj1CNB/BzhSHgAj1AOAMSSTB8AI9fHHEJLJAyBXH36MIak8AFL1wccQkssDIFUffIwhuTwAMvWhxxAyQh4AmfrQYwwZIQ+ATH3kMYSMkAdApj7yGEJGyAMgUR94DCFj5AHwdvVxxxAySh4Ab1cfdwwho+QB8Hb1cccQMkoeAG9VH3YMIePkAfBW9WHHEDJOHgBvUx91DCEj5QHwNvVRxxAyUh4Ab1MfdQwhI+UB8Db1UccQMlIeAG9RH3QMIWPlAfBy9THHEDJaHgAvVx9zDCGj5QHwUvUhxxAyXh4AL1Ufcgwh4+UB8DL1EccQsoQ8AF6mPuIYQpaQB8DL1EccQ8gS8gB4mfqIYwhZQh4AL1EfcAwhy8gD4CXqA44hZBl5AFyuPt4YQpaSB8Dl6uONIWQpeQBcrj7eGEKWkgfA5erjjSFkKXkAXKo+3BhClpMHwKXqw40hZDl5AFymPtoYQpaUB8Bl6qONEWRJeQBcpj7cGEGWlAfAZerjjSFkSXkAXKI+3BhBlpUHwCXq440hZFl5AFyiPt68bhSvHMevxvbbJz82ysfIA+AS9cGG+v8B/loeAJeojyBzvPL79be/zmh5AFymPsCsO3QcLQ+Ay9QHGkPIkvIAuEx9oDGELCkPgMvUBxpDyJLyAHhafYgxhGwlD4Cn1EeYXv0dZDt5ADylPsL06u8g28kD4Cn1EaZXfwfZTh4AT6mPML36O8h28gB4Sn2E6dXfQbaTB8BT6iOMEWQ7eQA8pT7EGD62kwfAU151aN91dOthWUn9XeMYeQA8ZZdj+1nHZz31GBlCDpAHwAeO7XqfozdhYXkAfODo7vc5ewsGywPgA8d3BkPIIfIA+JTjO5v3YCN5ADzEGM7kHdhAHgBPc3zn8BZsIA+Av/LZAXV823cwhCwqD4DLOL5rfObegWHyALiMI7zOZ+4NGCQPgMs4wGt85t6BYfIAuIwDvMZn7h0YJg+ASznAsz9v78JAeQBc7t4hdXSv/6yfGbd7P/cuRPIAYGFXDJghJJYHAAu7crgMIZE8AOAHQ0ggDwD4hRHkzfIAgF8YQt4sDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAKU8AABKeQAAlPIAACjlAQBQygMAoJQHAEApDwCAUh4AAJn/AZOzAKtBksxuAAAAAElFTkSuQmCC

[kyamagu]

Annotation will look like black, because each pixel will get annotation in integer value, like 0, 1, 2, .... These values are very close to black.