The invention relates to the technical field of 
image processing, and provides an image preprocessing device suitable for video coding. The device realizes the functions of 
macroblock zooming, 
image layer superimposing and 
thumbnail output of the 
source image in an online manner, and comprises a 
data source management module, a two-dimensional zooming module, an 
image layer superimposing module, an output module and the like. The 
data source management module pre-generates a 
source data read instruction required for the output of the current target 
macroblock row and buffers the 
source data; The 
image layer superimposing module reads out and pre-reads the 
macroblock data of the corresponding superimposed layer according to the coordinate position of each image layer. The output module obtains image data of corresponding size according to a fixed reduction multiple, and then outputs the image data to the 
video encoding module and writes the image data into the off-
chip memory. The device cooperates with the pipeline 
processing of each module through the block partition and ping-pong storage of the 
data source, which not only reduces the bandwidth consumption, but also satisfies thereal-time requirement of the high-definition video coding.