I mentioned the Jpeg tricks because they seemed interesting. We’re not talking of banks that misplace a few pennies, but of lossy compression methods (not just Jpeg) which get a big performance boost by understanding rounding bias.
It’s safe to say that I have more than a passing familiarity with Jpeg.
The compression “trick” I mentioned was designed to operate with any ordinary decompressor. (And obviously, reduction of the frequency of ±1 would immediately yield a Huffman code optimization.) The decompression “trick” I mentioned operates with any ordinary compressor. (Jpeg files can include custom markers for compressor-decompressor cooperation to get further improvement, but the tricks I described don’t require them.)
The tricks are so obvious that it may be a mystery why Jpeg did NOT explicitly incorporate them. I am aware of one company which kept its knowledge of these ideas secret to obtain a competitive advantage over “vanilla” implementations. (I had a hunch what they were doing and confirmed it with a code disassembler.)
People on the Jpeg-2000 committee (some of who were aware of my own paper on this topic) did add a new quantization parameter: