Hi,
In chapter 8.5.2.1.7, the collocated coordinates are derived according to the vertical position "( yP >> Log2CtbSizeY ) is equal to ( yPRb >> Log2CtbSizeY )" to know whether to select central luma location or bottom-right luma location.

This force to work always with the same Ctb row in the collocated picture and in the current picture.

But it is not explained what to do when the collocated Pb cross the right picture boundary. For example the top-right Pb of the current Ctb can have its collocated Pb outside the picture boundary if the current Ctb is the last Ctb of a picture row and it respect the "( yP >> Log2CtbSizeY ) is equal to ( yPRb >> Log2CtbSizeY )" equation.

In this case I see 2 solutions :
1) Central luma location is used instead.
2) The collocated Pb is marked as unavailable.

Regards,
Alexis

(Pb: prediction block, Ctb: coding tree block )