Where Is QRdo?

This was fun: A "Where Is Waldo" game for QR codes. Can you find it? Your phone can! The basic idea QR scanners don't see color. The first thing a decoder does is convert the image to grayscale — collapsing each pixel to a single brightness value via roughly 0.299·R + 0.587·G + 0.114·B — then binarize and hunt for the finder patterns (the three corner squares) and module grid. Everything downstream operates on luminance alone. That gap is the whole trick: luminance carries the code; hue and saturation are free to do whatever you want. You have two perceptual channels the scanner is blind to, and humans hunting for a pattern rely heavily on exactly those channels. So the code is rendered as a luminance difference — "dark" modules low-luma, "light" modules high-luma — but each module is painted a vivid random color at its assigned brightness. The key subtlety is that a fully saturated color's true luminance depends on its hue: pure blue sits around 0.11, pure red around 0.30, pure…