Homey will grab the image from the device at the resolution provide by the device. It basically just copies the file. If I look on the developer sight, the images from my cameras are full HD resolution.
As far as I know there is no way to scale an image up when casting as it will just send the image file and it’s up to the device to scale it to fit the display.
I also use PipUp to send images to my TV and with that I can specify the size of the popup window then the TV scale the image to fit the popup.
