Mask count

[tschaub]

Reading the spec, I'm uncertain what is allowed in terms of the number of masks (full and reduced resolution).

I think that working with GeoTIFFs in GDAL, there is only support for a number of masks equal to or less than the number of "images" (full and reduced resolution). In addition, the resolution of each mask must match the resolution of a corresponding image. In other words, an image has an optional mask.

(I'm using the word "image"here as shorthand for an IFD where bit 2 of the TIFF Tag NewSubfileType is not set and using "mask" otherwise.)

Does the OGC COG spec have any requirements about the number and resolution of the masks? I can't find anything in 7.2.1. Requirement Reduced-Resolution Subfiles or elsewhere in the spec.