14 bit AD is usually used to acquire and process the detector′s analog output in thermal imaging systems while most display devices only required 8 bit video signal,thus gray translation should be carried out.Plateau histogram is a common translation method,but it needs large memory and processing time.Usually a special memory chip is required in the process.The memory requirement can be reduced largely by the proposed method.It makes sampling statistics,compresses the previous gray level and set a suitable maximum plateau value.All the work can be done in a single FPGA.Experiments prove that the method works well.