[magick-users] "Quality" of JPEG images

[Wolfgang Hugemann]

I am quite happy with IM preserving the JPEG quality by default, i.e. 
producing a JPEG output of comparable size as long as the dimensions of 
the picture are not altered.

But how exactly does IM identify the JPEG quality when I use the command
identify -verbose test.jpg

? Having tested this with different image sources, I suspect that this 
just evaluates a JPEG header field. Depending on the program source of 
the image, the same photo can have quite deviating "quality" though the 
JPEG files have almost the same size.

Any ideas?

Wolfgang Hugemann