Panorama Rotation Node gives output not equal input even with no changes

[Yevhen-K]

I have Substance Designer 12.1.1 build 5825

When I use such scheme

input bitmap is in .exr format (32bit float or 16bit half-float) 

panorama Rotation (all parameters are at default values)

blend node with subtract option - there are differences, but the images must be the same!

Under differences I mean histogram Used Range values (see below)

They are quite big (maybe with this current image), but this is math: if no changes - there must be no difference.

If I connect input bitmap to both blend node inputs that range is 0;0, and that is correct.

The same error persists in any different resolution and with .hdr format images.

Only one thing I've found so far - when inserting exposure node just after the image and make exposure lowering - the error gets smaller too, but it is not 0 in any way.

[Luca Giarrizzo]

Hello,

Thank you for the detailed report!

The differences are caused by the cumulated imprecisions in the way rotation is computed. A big part of these imprecisions are related to the limitations inherent to floating point arithmetic.

We are assessing this internally, I appreciate your patience in the meantime.

Best regards.