Process images with more than 3 channels

[maiskovich]

Hello, thank you for the great package.

I am trying to process images with 30 channels (CycIF) in tiff format.

I am running the examples provided in the readme, and I am getting back JPEG tiles with three channels. I assume that the first three channels of my images are being picked.

Is there a supported way to deal with these types of images? I was checking the backend definition files, and based on the use of OpenSlide, it seems that it will not be supported to use images with more than three channels (openslide/openslide#42). Do we need to develop a new backend type for these images?

Thank you