Photoshop JPEG from RAW Vs. In-Camera JPEG File Size

I have a 350D, and I almost always shoot in RAW + JPEG mode. I've noticed that if I process a RAW file and save it as a JPEG as best quality (10) using Photoshop, the file size is about half the size of the JPEG created by the camera from the same picture.

Does anyone know what accounts for the difference? Is the camera using an algorithm that saves time at the expense of less compression? I know the camera is saving time at the cost of something because it has limited computing power, of course. However, I thought quality would take more of a hit than file size.

Thanks for any information!

The camera throws away less data than a Q10 JPG. Save as Q12 if you're using photoshop, that might be even larger than the camera JPG.

I noticed the same thing when converting RAW to Jpeg using Canon's own DPP. I haven't heard, or taken the time to look too closely, to see whether that makes any noticable difference in image quality. Here's what I saw with my Rebel XT:

Full Quality out of camera Jpeg ~3mb
DPP Set to highest quality Jpeg ~6mb
DPP Set to second highest quality Jpeg ~1.5mb

All of these are big differences... big enough that I wondered if anyone out there has been shooting RAW only, and then convering all to Jpeg later simply because file size/quality is better? (Plus save card space vs. RAW+JPEG.)

Currently, I'm still shooting RAW+JPEG, since I like having jpegs right away, and don't have a workflow where I batch convert images immediately after transfering them to my computer.

Noise and shadow detail are reduced using the default in camera jpg processing.

tim wrote in post #2414826
The camera throws away less data than a Q10 JPG. Save as Q12 if you're using photoshop, that might be even larger than the camera JPG.

Okay, I thought Q10 was the highest JPEG quality setting in Photoshop. I just tried Q12, and you're right. With Q12, the JPEG file processed with Photoshop is larger.

The problem was simply that I thought I was using Photoshop's highest quality setting, but I wasn't.

Thanks for the comments, everyone!