Compression algorithm for screen images

which comes from the Computer Screen

is an important task in the Screen Share technology. Traditional methods are based on the algorithms such as RLE

LZW or JPEG directly

which cannot meet the requirements of both the quality of recovery image and compression ratio to compress screen image respectively. High compression ratio algorithms (JPEG) result in a low quality of image

while no-distortion algorithm (RLE

LZW) leads to a low compression ratio. In order to resolve this contradiction

an effective compression algorithm based on dynamic threshold sub-blocking is proposed in this paper. Before the image compression

Screen image is divided into four sorts of blocks by certain provided rules first

which are named as Pure-color Blocks

Text Blocks

Icon Blocks

and Image Blocks. Then these blocks are compressed separately depended on their characteristic so as to ensure that the quality of recovery image is the overall best and the compression ratio is the highest. Pure-color Block

Text Block

and Icon Block are compressed with no-distortion compression algorithm

and Image Block is compressed with JPEG algorithm. Result of experiments shows that our algorithm has improved quality of recovery image

higher compression ratio

and higher compressed speed than traditional algorithm.