My RGB332 Color Code Oversight

I felt a certain level of responsibility after my library was accepted to the Arduino library manager, and wrote down all the things I knew I could work on under GitHub issues for the project. I also filled out the README file with usage basics, and I had felt pretty confident I have enabled people to generate color composite video out signals from their ESP32 projects. This confidence was short-lived. My first guinea pig volunteer for a test drive was Emily Velasco, who I credit for instigating this quest. After she downloaded the library and ran my examples, she looked at the source code and asked a perfectly reasonable question: “Roger, what are these color codes?”


Having many years of experience playing in computers graphics, I was very comfortable with various color models for specifying digital image data. When I read niche jargon like “RGB332”, I immediately know it meant an 8-bit color value with most significant three bits for red channel, three bits for green, and least significant two bits for blue. I was so comfortable, in fact, that it never occurred to me that not everybody would know this. And so I forgot to say anything about it in my library documentation.

I thanked Emily for calling out my blind spot and frantically got to work. The first and most immediate task was to update the README file, starting with a link to the Wikipedia section about RGB332 color. I then followed up with a few example values, covering all the primary and secondary colors. This resulted in a list of eight colors which can also be minimally specified with just 3 bits, one for each color channel. (RGB111, if you will.)

I thought about adding some of these RGB332 values to my library as #define constants that people can use, but I didn’t know how to name and/or organize them. I don’t want to name them something completely common like #define RED because that has a high risk of colliding with a completely unrelated RED in another library. Technically speaking, the correct software architecture solution to this problem is C++ namespace. But I see no mention of namespaces in the Arduino API Style Guide and I don’t believe it is considered a simple beginner-friendly construct. Unable to decide, I chickened out and did nothing in my Arduino library source code. But that doesn’t necessarily mean we need to leave people up a creek, so Emily and I set out to build some paddles for this library.

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