MATLAB: Prepare an RGB image for digit and letter recognition
First, many OCR programs automatically perform image processing, including possible color conversion, image filtration, dilation/erosion, and monochrome conversion, in order to improve the quality of OCR operation. Especially good in this are neural-network enabled cloud-based OCR applications.
If you absolutely need local MATLAB program to perform the image processing supposedly preparing the document for recognition, first check if MATLAB or its addons have some kind of image thresholding function: the function which outputs a monochrome (black/white) image given a scanned document. If there is no ready thresholding function, you can try and code it. An introduction into a computer graphics required to successfully code an image preparation operations &quot;for digit and letter recognition&quot; you will find in https://tesseract-ocr.github.io/tessdoc/ImproveQuality and elsewhere, if you search words and phrases highlighted in this answer.
You may find useful this ref, which, although lacking MATLAB code, contains code snippets written in common computer languages.