Capital Letters Make Smaller QR Codes: A URL Encoding Mystery

Two QR codes pointing to the same URL, one larger than the other. Why? The answer isn't error correction, but encoding mode. A URL in all capital letters uses the more compact alphanumeric mode, while lowercase uses byte mode, leading to data redundancy and a larger QR code. This highlights the impact of character set choices in URL encoding on QR code size. For the smallest QR code, use uppercase letters.