What are some method for pre-processing data in OCR?
You can do image tresholding, normalize the data first by dividing each elements of the vector by 255, then do thresholding, for each $x_i \in \mathbb{x}$ $x_i=1$ if $threshold\le x_i$ where $\mathbb{x}$ is your data vector, and $x_i$ is the element of vector, you can choose the threshold based on experiment or personaly I choose 0.5. By doing image thresholding we reduce the noise of the image, hence its increase the accuracy