Alpha Deblocking and Beta Deblocking

How To Use Mpeg4 AVC Deblocking Effectively (Small FAQ)

In X264there are two deblocking parameters, called Deblocking strength and Deblockingthreshold. The strength parameter refers to Alpha Deblocking,while the Threshold Parameter refers to Beta Deblocking (Alpha andBeta Deblocking are the official names). When a deblock setting is written asX:X (for instance 0:0 or 2:-2) the first number is alpha deblocking, while thesecond is beta deblocking.

 

 Alpha deblocking effects the overal amount ofdeblocking to be applied to the picture, higher values deblock moreeffectively, but also destroy more detail and cause the entire image to besoftened. The default value of 0 is almostalways sufficient to get rid of most blocking (especialy when using a cqm),but leaves the picture noticibly blurier. In general use this value should beno lower than -3 and no higher than 3.When using a cqm the authors recomended settings should be used as the defaultvalue, and shouldn't be altered by more then +/-2. Alpha Deblocking is the mostimportant parameter in determining the overal sharpness of your encode.

 

 Beta Deblocking is a bit more tricky to use, BetaDeblocking determines whether something in a block is adetail or not when deblocking is aplied to it. Lower valuesof Beta Deblocking apply less deblocking to more flat blocks with detailspresent (but more deblocking to blocks without details), while Higher valuescause more deblocking to be applied to less flat blocks with details present.Generally Beta Deblocking shouldn't be altered unless you are haveing problemswith the default setting. Raising Beta deblocking is a good way to help get ridof ringing artifacts by aplying more aggressive filtering to blocks that aren'tvery flat. Lowering beta Deblocking is a good way to reduce the amount of DCTblocks without bluring the entire picture. A high value of beta deblocking willcause nonflat blocks to be deblocked more aggressively, while a low value willcause the opposite.

 

 If you wan'tto give your encodes a more detailed look and don't mind the occasional blocktry a setting of -2:-1. If you like a clean picture and don't mind a littlebluriness try 1:2. A nice trick for anime is to use lower beta deblockingsetting because it won't blur out lines as much that way.