Changes Between ImageMagick 6.4.2-10 and 6.5.2-8?

[luwenbin]

I used ImageMagick 6.4.2-10 for some days and today changes to version 6.5.2-8. Then I found the issue that,
For the same picture operation which resize a 1540x2320 jpg file(2.56Mb) to a 600x900 one,
with 6.4.2-10, the output file is 509Kb
with 6.5.2.-8, the output file is 183Kb, and the speed is much more faster
Because the differences of the output file size is too much, so I don't know whether it is correct. Can anyone explain this to me? Thanks in advance
By the way, I use the command "convert -resize" to the same jpg file, and found the same issue, for different version of ImageMagick, the output file sizes have great difference.

[magick]

Most likely its the default image compression quality. You can set it yourself with -quality 92, for example.