In raw format each pixel is a byte of data... So those two numbers are equivalent. When you save as a jpeg, you are using compression. You do not loose any pixels doing this, but you save the information (or most of the information) more efficiently. Photoshop doesn't split apart pixels unless you ask it to, by, for instance, resizing the image to something larger than it was before. 12 in photoshop does not make the image larger. I am 95% certain it represents 0% compression. Whatever level you choose it will not change the number of pixels in your image. It should only change the level of compression (I usually choose something near the middle).