1. A data editing apparatus, comprising: a processor; a database, in communication with the processor, that stores a processing result for each character that constitutes a certain character font set, the processing result being obtained by performing image processing on a raster image of each character to simulate how an image is viewed under a certain visual characteristic; an HTML analysis section, executable by the processor, configured to analyze an HTML document and retrieve processing results for characters corresponding to characters contained in the HTML document from the database; and a modification element locating section, executable by the processor, configured to locate an HTML element that needs to be modified in the HTML document, the step of locating being based on the processing results for the characters retrieved by the HTML analysis section, the sections for enabling particular readability of the certain data on a display; wherein the HTML analysis section is further configured to, based on readability of a web page to be generated from the HTML document, determine whether to: entirely perform rendering and image processing for the HTML document, partially perform rendering and image processing for the HTML document, or perform no rendering and image processing at all for the HTML document.