JPEG Quality Settings

[quickie]

Hi.

I've saved a 6.82MB jpeg using the default (92%) setting (ie no -quality setting provided by me) and got a 6.08MB file, which is about what I'd expect. I then tested the same original file with a write using a quality setting -quality 92%%. This time I got a file size of 4.2MB. That's a 2MB difference. Where did the 2 megs go when I used a quality setting rather than leaving it up to IM?


Thanks.

[fmw42]

In writing jpg, IM tries to find the input quality and use that if it can otherwise it uses the default 92. So IM found some input quality and used that when you did not specify 92.

see -quality http://www.imagemagick.org/script/comma ... hp#quality

"The default is to use the estimate quality of your input image otherwise 92."