the detailed explanation of the present invention is described as follows . the described preferred embodiments are presented for purposes of illustrations and description , and are not intended to limit the scope of the present invention . according to an embodiment in reference to fig1 and fig2 a , the encoding method of screen frame adaptively changing the image quality includes the following steps . first , at least one motion region 21 , 21 ′ and at least one motionless region of a screen frame 2 are identified ( s 11 ). according to an embodiment , motionless region is the region of the screen frame 2 outside the motion regions 21 , 21 ′. it is noted that a screen frame may include a plurality of motion regions and motionless regions . according to an embodiment , the motion region is obtained from comparing the difference between each pixel of the screen frame at two given time periods . for example , by performing an xor operation on each corresponding pixels of two consecutive screen frames , the motion region of the later screen frame is identified . then , at least one motion encoding region covering the motion region identified in step s 11 is determined ( s 12 ). as illustrated in fig2 a , the motion region 21 is covered by the motion encoding region 22 . according to an embodiment , the motion encoding region is rectangular . it is noted that a single motion encoding region can cover but not limited to a plurality of motion regions . a single motion region can also be covered by a plurality of motion encoding regions . as illustrated in fig2 a , the motion region 21 ′ is covered by the motion encoding regions 22 a , 22 b , 22 c , 22 d and 22 e . in other words , the motion encoding region may cover a portion of the motion region or a plurality of motion regions . next , a motion image quality is decided , and the motion encoding regions 22 , and 22 a - 22 e are encoded based on the motion image quality . according to an embodiment , the size of the motion encoding region is one of the deciding factors of the motion image quality . for example , the motion image quality may be inversely proportional to the size of the motion encoding region ; i . e . the larger the motion encoding region , the lower the motion image quality selected for encoding . besides , different image qualities can be respectively selected for the plurality of motion encoding regions . referring still to fig1 , at least one motionless encoding region covering the motionless region is determined ( s 14 ). by the same token , the motionless region may be rectangular , and a single motionless encoding region can cover a plurality of motionless regions , or a single motionless region can be covered by a plurality of motionless encoding regions . next , a motionless image quality is decided and the motionless encoding region is encoded based on the motionless image quality ( s 15 ). it is noted that the motionless image quality is better than the motion image quality . in short , the encoding method of the screen frame changes the image quality adaptively , wherein the motion region of the screen frame is encoded at a lower image quality and the motionless region of the screen frame is encoded at a higher image quality . according to an embodiment , the motionless image quality can be but not limited to be lossless , so as to fully present the regular patterns in the screen frame . with the screen encoder repeating the steps to process the screen frames in series , the video region of the screen frames can be played smoothly while the motionless region is displayed at a better image quality . the encoding method of the present invention has not employed the complicated algorithms , such as motion estimation and motion compensation , etc ., and hence occupies less system resources and has a shorter latency . according to another embodiment in reference to fig3 and fig2 b , the encoding method of screen frame changing the image quality adaptively includes the following steps . first , at least one motion region 21 in the screen frame 2 ′ ( s 31 ) is identified ; then at least one motion encoding region 22 covering the motion region 21 is determined ( s 32 ); then a motion image quality is decided , and the motion encoding region is encoded based on the motion image quality ( s 33 ). the detail description of the steps has been provided above and would be skipped here . continued from the above description , the encoding method of the screen frame further includes the following steps . to begin with , the motion encoding region is added to a historical list ( s 34 ). then , at least one motionless region is identified from the motion encoding regions in the historical list ( s 35 ). for example , the motion encoding region 22 may be added together with a time stamp into the historical list . this way , after a certain time periods , part of the motion encoding region or the entire motion encoding region that has not changed can be identified as the motionless region . as illustrated in fig2 b , the window 23 , which includes a motionless content , overlaps partially with the motion encoding region 22 . after a certain time period , the shaded overlap region is regarded as a motionless region 24 . then , at least one motionless encoding region covering the motionless region 24 is determined ( s 36 ). in this embodiment , the motionless encoding region is equivalent to the motionless region 24 . then , a motionless image quality is decided and the motionless encoding region is encoded based on the motionless image quality ( s 37 ), wherein the motionless image quality is better than the motion image quality . finally , the motion encoding region corresponding to the motionless encoding region is removed from the historical list ( s 38 ). as illustrated in fig2 b , according to an embodiment , the motion encoding region 22 and the motionless encoding region are nonoverlapping regions so as to avoid duplicate operations on the overlapping regions . according to an embodiment in reference to fig4 , an electronic device applies the encoding method of screen frame to the transmission of screen frames with adaptively changed image quality . the electronic device includes a processor unit executing a transmission method of the screen frame so that the receiving end can display the screen frame transmitted by the electronic device . according to different embodiments , the electronic device can transmit the screen frame through wired or wireless communication . the transmission method includes : identifying at least one motion region ( s 42 ); determining at least one motion encoding region covering the motion region ( s 43 ); deciding a motion image quality , encoding and transmitting the motion encoding region ( s 44 ); identifying at least one motionless region in the motion encoding region ( s 46 ); determining at least one motionless encoding region covering the motionless region ( s 47 ); and deciding a motionless image quality , encoding and transmitting the motionless encoding region ( s 48 ), wherein the motionless image quality is better than the motion image quality . the detail description of the steps has been provided above and would be skipped here . according to an embodiment , the transmission method further includes a step of adding the motion encoding region to a historical list ( s 45 ) after the motion encoding region is transmitted . then , the motionless region is identified from the motion encoding regions in the historical list in step s 46 . besides , after the motionless encoding region is encoded and transmitted , the motion encoding region corresponding to the motionless encoding region is removed from the historical list ( s 49 ). according to an embodiment still in reference to fig4 , the electronic device can transmit a full screen frame initially ( s 41 ). thereafter , the electronic device can transmit only the motion encoding region and the motionless encoding region required to be updated with steps s 42 ˜ s 49 . the receiving end would receive the initial full screen frame and the subsequent motion encoding regions and motionless encoding regions to reconstruct the screen frame . for example , suppose the window 23 in fig2 b is under the motion encoding region 22 originally . after the full screen frame 2 ′ is transmitted , only the motion encoding region 22 including the video is required to be transmitted subsequently . when the window 23 is moved to be on top of the motion encoding region , only the shaded motionless region 24 is updated with respect to the screen frame 2 ′. therefore , the transmitting end only needs to transmit the motionless encoding region and the motion encoding region 22 that is not covered by the window 23 for reconstructing the screen frame . to summarize the foregoing descriptions , the encoding method of the screen frame and the electronic device applying the same encode the motion region of the screen frame at a lower image quality so that a smooth video is presented on the receiving end , and encode the motionless region of the screen frame at a higher image quality so that a higher quality motionless image is presented simultaneously . besides , the encoding method of the screen frame of the present invention has not employed the complicated algorithms of motion estimation and motion compensation and therefore requires less system resources , avoids affecting other jobs of the user when running as a background , and is more suitable for real time applications due to lower latency . while the invention is susceptible to various modifications and alternative forms , a specific example thereof has been shown in the drawings and is herein described in detail . it should be understood , however , that the invention is not to be limited to the particular form disclosed , but to the contrary , the invention is to cover all modifications , equivalents , and alternatives falling within the spirit and scope of the appended claims .