Optimal scanning algorithm produces contour on the image which is very rich in color, the algorithm will adopt non-linear calibration and eliminate the contour of image. Firstly, find out the relationship between the gray level and pixel data of the optimal scanning algorithm, and get the reason of contour with the traditional pulse-width modulation (PWM) gray-scale strategy comparison. Then according to the human eyes have different feelings on different gray error images, the gray error is classified as acceptable error and unacceptable error. Next, rearrange all possible optimal scanning gray weights by MATLAB, and exclude composition comprising an unacceptable error. Therefore, the rest combinations have good linearity. Finally, calculate the data transmission frequency at different display resolutions, experimental results show that the number of contour lines from 13 becomes 0 when the weight values of 8 bits turn to 208:104:52:24:14:8:3:1 for 256 level gray-scale images. The contour lines disappear by OLED-on-silicon microdisplay, image quality is improved, and in ultra-high resolution, system clock frequency is lower than the tradition field scanning method, it has a great advantage in reducing system cost.