Raw File sizes ?

Can anyone who shoots Raw with either istD or istDS tell me what sort of file sizes they get shown after saving the Raw images to Windows XP. I am getting between 9500 KB and 11,800 KB file sizes recorded where I would have expected about 18,000KB ( 6 Megapixels x 3 bytes/pixel = 18,000).
Is something wrong with my thinking ?

in fact Raw files are only 12 bits per pixel - each of the pixels is one of red green or blue. The raw conversion software then 'guesses' what the other two colours would be based on the adjacent pixels of those colours. In theory then the files should be about 9 megabytes. However I think Pentax must use 2 bytes per pixel and then have some modest compression - that seems the only explanation for the variable file sizes (unless someone knows better....)

Well Tony, don’t forget that as well as the approx 9Mbytes for the image there is also the metadata – all the information about the image, camera settings, date, time, colour temperature etc. This may or may not be used by your RAW converter depending on your preference.

Regards,
Dave.

True - but that can't be more than a few kilobytes, which is a drop in the bucket compared to 9 megabytes.

There may also be a small jpeg thumbnail image that the RAW converter displays. The camera must generate one for its own display so that could also be saved with the file. I guess most photographers don’t want to know all this but like you Tony I am interested!

Dave.

Thanks guys. You are quite right, it pays to read the Manual thoroughly - ie Page 31 states that 128MB memory card can hold 11 Raw images, therefore 128/11 = 11.6MB per image. I thought I had read it somewhere that each image was about 18MB.