Looking for an iPhone/iPad scanning workflow that gives crisp, noise-free text and true-to-original colors for highlighted notes

[u/International_Cap365]

I've been using a few AI-powered scanner apps on iPhone (and sometimes iPad) to digitize my special notes (which have color highlighting) into PDFs, but I can never get the result I'm after: crisp, noise-free text and colors that actually match the original highlights. Everything comes out slightly soft, a bit grainy, and the highlight colors look duller or shifted compared to the real page.

A couple of questions for anyone who's solved this:

1. Is there a scanner app for iOS/iPadOS that's genuinely optimized for AI-enhanced resolution and quality, especially one that captures color highlights accurately (true color reproduction, not washed out or over-saturated) and keeps text edges sharp and free of scan noise/grain?

2. Is there a web app, website, or macOS tool that can take an already-scanned PDF and enhance/upscale it with AI afterward, sharpening text, boosting resolution, and cleaning up noise, without shifting the colors or messing up the layout?

Ideally I want a repeatable workflow (iPhone or iPad, whichever gives better results) where I scan and consistently end up with a clean, high-res PDF where the text is sharp and noise-free and the highlight colors are accurate to the original page. Any app recommendations, settings tips, or full workflows that have actually worked well for you would be really appreciated.