What are good “quality” settings for JPEG?
Most JPEG compressors let you pick a file size vs. image quality tradeoff by selecting a quality setting. There seems to be widespread confusion about the meaning of these settings. “Quality 95” does NOT mean “keep 95% of the information”, as some have claimed. The quality scale is purely arbitrary; it’s not a percentage of anything. In fact, quality scales aren’t even standardized across JPEG programs. The quality settings discussed in this article apply to the free IJG JPEG software (see part 2, item 15), and to many programs based on it. Some other JPEG implementations use completely different quality scales. For example: • Apple used to use a scale running from 0 to 4, not 0 to 100. • Recent Apple software uses an 0-100 scale that has nothing to do with the IJG scale (their Q 50 is about the same as Q 80 on the IJG scale). • Paint Shop Pro’s scale is the exact opposite of the IJG scale, PSP setting N = IJG 100-N; thus lower numbers are higher quality in PSP. • Adobe Photoshop doesn
