jpeg size query

I shot a photo with my 60D, I used RAW+jpeg, the jpeg is 8mb, I then opened the RAW file in DPP and converted to jpeg with the same in camera settings, the jpeg from DPP is 12mb.

Why the 4mb difference in size, is it only because the camera is using more compression than DPP?

JPEG has a lot more parameters than just "more or less compression".

What I recommend you do is put the raw file into postprocessing program. Then open both JPEG variants as layers in the same image. Then turn on one of the jpegs only and use the "difference" layer mode. Compare everything to everything. It will tell you pixel by pixels where your file size went.

In general the quality of the JPEGs produced by Canon's in-camera processors and parameters picked is pretty good. My expectation is that you'll find the 4 MB towards the other JPEG extra wasted. The raw file will show more of a difference of course.

Joe52 wrote in post #12011221
I shot a photo with my 60D, I used RAW+jpeg, the jpeg is 8mb, I then opened the RAW file in DPP and converted to jpeg with the same in camera settings, the jpeg from DPP is 12mb.

Why the 4mb difference in size, is it only because the camera is using more compression than DPP?

Yes, the difference is one of compression. The camera offers only three levels of compression because of "space" limitations, but DPP can use a more expansive set of algorithms and offer a wide range of choices. In fact, at one point in it's history (I'm afraid I don't remember which edition) DPP changed iis jpg compression engine, expanding the range by making the 10 end of the scale much less compressive. Level 7 or 8 does roughly the same compression as the camera's Fine setting.
As u0pt said, level 8 is plenty good for most uses, especially if it is not going to be resaved many times.

Thank you both for the info.