IBA::channel_append() / oiiotool --chappend and oiitool --chnames

IBA::channel_append() (exposed as oiiotool --chappend) takes two input images and produces an output that is the channels of the two images appended to each other.

oiiotool --chnames lets you rename some or all of the channels of an image.

Here's an example of how this might be used to take an RGBA file and a separate Z file, and combine them into a single RGBAZ file (and make sure that the last channel is named "Z" regardless of what it was called in the image it came from):

    oiiotool rgba.exr z.exr --chappend --chnames ",,,,Z" -o rgbaz.exr