Intra prediction applied in H.264/AVC improve compression efficiency greatly of I frame.But the full search algorithm is computationally expensive and there exist conflict with some real time application and embedded systems just holding limited calculation resource.In order to promote prediction speed

a fast intra prediction algorithm is proposed which select appropriate coding block size based on complexity of the image

use annular slide window to select prediction mode dynamically and define a simple block match regulation.Experiments prove it is so practical and valid that the match speed has been doubled while the quality of reconstruct picture is nearly not decrease.