I had something like the following in the view xml:

<field name="chart_file_name" readonly="1" invisible="1"/>
<field name="chart" widget="image" img_width="400" img_height="300" filename="chart_file_name"/>

The image resized as I expected with the image_width/img_height tags.  But the filename tag did not work.  When I did "Save image as" on Chrome, the default file name was "image.jpg".

Questions:

1. Is there a way to specify the default file name of the Save As dialog?
2. I found the "filename" tag in https://www.odoo.com/documentation/10.0/reference/views.html but not the image_width/img_height tags.  Did I go the the wrong document?