Flash file with *only* one image double the size if the image?

programming flash
1

I have a Flash file.
All I’ve done is to stick in one image file.
I’ve got the image publish setting to be 100%.

I publish the file.
The resultant SWF file is double the size of the image.
I would have thought that it should be the same or just a tiny bit bigger files size than the image.

(The image itself is an image I edited in Photoshop… and optimised for the web.)

Where am I going wrong?

Thanks.

OM