[M4IF Technotes] Re: [M4IF Interop] Sprite brightness change?

[Yoshinori Suzuki]

Dear Dr. Huber,
Thank you for the comments on brightness changes.
I have a comment on the GMC specification.
Kris Huber wrote:
> 
> Hello all,
> 
> Are there any test bitstreams exercising brightness change for the low
> latency sprite or GMC case?  I've noticed some ambiguity in MPEG-4 visual
> about how it is done, especially relative to how I think it should be done.
> 
> Information about specs related to MPEG-4 visual in which
> sprite_brightness_change is required to be 0 would also be appreciated
> (ISMA?, existing implementations?).
> 
> I'll make a report of this MPEG-4 problem to individuals who may have
> opportunity to address it soon within the MPEG organization.  Please reply
> in the next day or two, and there is a chance that your view can be
> incorporated into the next MPEG visual problem report.

I am an original proposer of the GMC to MPEG.
First, I would like to make it known to you that 
"the GMC does NOT support the brightness change tool".
The sprite_brightness_change is the tool for sprite warping, 
not for the GMC prediction. 
However, that is not indicated the document clearly as you pointed out.
So, I think that we should add the following sentence to the 
semantics of sprite_brightness_change for clarification:
sprite_brightness_change: This is a one-bit flag which when set to '1' 
indicates a change in brightness during sprite warping, alternatively,
a value of '0' means no change in brightness.
Note that this vaule shall be '0' when sprite_enable == 'GMC'.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Any comments?
Best regards,
Yoshinori Suzuki
Hitachi, Ltd.