A practical starting point is to study existing open-source imaging libraries rather than trying to build everything from scratch.

Two useful examples mentioned by the community are:

• ImageMagick: a widely used image-processing toolkit. Reading its source can help you understand common image manipulations and processing pipelines.
• Little CMS (lcms): a popular library for color management, useful for learning how color spaces and color conversions are handled.

In general, many developers do rely on established libraries for core tasks such as image I/O, color management, and standard transformations, then build custom algorithms on top of them. So no, not everyone is reinventing the wheel.

For your interests, a good path is:

1. Learn image fundamentals: pixels, bit depth, color spaces, gamma, and compression.
2. Study common formats, especially JPEG and RAW workflows.
3. Explore source code in mature libraries like ImageMagick.
4. Use a color-management library like lcms to understand accurate color handling.

That combination gives you a solid base for later tackling more advanced topics like denoising, HDR, exposure adjustment, and retouching tools.