Rasterizing image makes file larger

[brettd19197606]

I am designing a large banner and I have a large jpeg image on it. The file size is huge so I tried to rasterize it so I could send it to the print shop. I've done this dozens of times and it always reduces the file size. This time, it is doubling the file size. I have no idea why that would be happening.

Does anyone have any idea or another way I can reduce the file size?

[meganchi]

Are you saving it with a lower resolution, like 150 dpi? You wouldn't need a 300 dpi for a banner.

[S_Gans]

I'm sorry. Your question is confusing to me. Perhaps you can clarify? Rasterizing a large jpeg in an image would give you exactly the same number of pixels as exists in the original image. If you've ever had the file size shrink, it's likely because you were using a large jpeg, in a smaller space, so rasterizing threw out some pixels. 

Rasterizing is simply conversion to pixels, and it depends on the width and height of the original image, and the resolution to which you're rasterizing. 

Is it possible you're using a large image, that's not being shrunken to fit your Artboard, and you're also using high resolution? Or even more - are you using a jpeg (raster) image that's actually smaller than the artboard, and rasterizing is adding pixels?