Photoshop: Filter > Filter Forge greyed out

I'm trying to apply a filter I created to a 16-bit depth greyscale 32768x32768 image. Whenever I try to apply the filter in the standalone application, it crashes with the "Bad Allocation" error.

I read on these forums that I should try from within Photoshop, using the plugin version, however, whenever I open an image larger than 30000x30000, the Filter Forge option is greyed out. Is this a limitation of the software?

I'm using the latest version of Filter Forge (6.008 x64) and the latest version of Photoshop (CC 2017). I have 16 GB of DDR4 RAM and have allocated a huge amount of virtual memory on my non-SSD harddrive (~200GB).

Hi! Thanks for the reply. I tried changing the mode to RGB mode, and also tried changing the bit depth but the Filter Forge option remained greyed-out.

I managed to solve my problem by performing the render in standalone mode and *further* increasing my virtual memory to 500GB. It took around 18 hours due to the constant thrashing, but I finally got an output image without a Bad Allocation error. According to my task manager the virtual memory use got as high as ~250GB so I wasn't too far off with my original virtual memory settings.