The default readout configuration for the H4 swaps direction between channels: <-- -> <- -->, etc. But the ASIC internally corrects this so that the delivered image has all pixels sequenced from left-to-right. Fine.

Fine, until you use IRP, especially N:1 IRP with N>1. Then that scheme gets very confusing: since the origin of the IRP sequence is at the start of the readout we will need to interpolate accounting for that orientation, but making the readout orientation the same for all channels by flipping alternate ones then makes the channel images flip to the wrong order.

But that H4 readout ordering can be changed to --> --> --> -->, etc. I think that would make life less confusing and processing code less buggy: we still need to process the channels individually for non-trivial interleaving, but at least we won't need to flip back&forth. For non-IRP, there is essentially no difference unless you are hunting down injected electronic noise, etc. For the existing 1:1 IRP reads there is also little difference: since each data pixel is paired with its one reference pixel the reference image does not need interpolation.