In multimedia application systems

recently emerging the need of compressing and transmiting a special video in Internet

which has the characters of full screen

half motion and non-continuous tone

for example

the content of PowerPoint files. In order to satisfied this need

this paper proposed an efficient scheme to acheive the high compressed ratio at the same time protecting the nearly lossless visual quality. This scheme is named "sharing screen" and includes the two main techniques

one is called copy-screen

and the other is the data-compression method called LZ77. The first step of this scheme is to copy the full and high resolution screen contents and save them as bitmap formats. The second step is to reduce the color resolution of these bitmap images

transforming the 24bit color definition into 4 or 8 bit color definition so that we can reduced the quantity of image data. The last step is to apply the lossless method to compress the low color resolution images. As to the non-continuous tone color images

the compressed ratio can reach up to 100:1

and it has real time performance

moreover

the decode process is fairly simple. So it can be easily used in network multimedia applications such as Distance Education and Remote Stock Comment & Analysis System.