1. An image correction method applied to a scanner device, the scanner device including a main case, a drive module, an optical module, an analog-to-digital converter, a first-in and first-out data buffer, a data flow control unit, a set unit, a data classification unit and a memory storage unit which are electrically connected and assembled in the main case, a top of the main case being disposed with a scanning platform, the image correction method comprising steps of: positioning a document which is ready to be scanned on the scanning platform of the scanner device; the scanner device initializing parameters before scanning the document; the drive module driving the optical module to move to make the scanner device begin scanning the document to form one scanned line of the image which includes a plurality of image pixels corresponding to a red light, a blue light and a green light; the image pixels corresponding to the red light, the green light and the blue light of the one scanned line of the image being converted into digital signals, namely pixel values corresponding to the red light, the green light and the blue light, via the analog-to-digital converter, the first-in and first-out data buffer reading the pixel values corresponding to the red light, the green light and the blue light in sequence, and the set unit setting a program statement in the data flow control unit for getting values which are composed of an update shading table; the pixel values corresponding to the red light, the green light and the blue light of the one scanned line of the image being classified by the data classification unit, and together with the program statement which is set by the set unit being transmitted to the memory storage unit, a storage area of the memory storage unit being divided into a plurality of memory positions for storing values of variables which are needed by the scanner device for executing the program statement set by the set unit; the scanner device judging whether the image is scanned sufficient, if the image being judged to be scanned sufficient, execute the next step, and if the image being scanned insufficient, returning to repeat executing the step three, the step four and the step five until the image is judged to be scanned sufficient by the step six; the scanner device executing the program statement set by the set unit in the memory storage unit to get the values for building the update shading table; and the scanner device utilizing the update shading table to compensate the pixel values corresponding to the red light, the green light and the blue light of each scanned line of the image for doing a luminance compensation of the image pixels corresponding to the red light, the green light and the blue light of each scanned line of the image so as to complete an image correction of each scanned line of the image.