I don't know how camera specific this black frame is, but in my HP 945is it is explaned thusly ....
"At longer shutter speeds the camera will automatically take a second exposure with the shutter closed in order to measure and reduce the noise (grainy look) in the image. In these cases the exposure will seem to take twice as long as expected. For example, in a 1-second exposure, the active display will stay dark for 2-seconds until the noise reduction frame is exposed. This means that at longer shutter speeds, you may not be able to take quite as many shots back-to-back." To me this reads that for each extended exposure there will be a matching dark frams taken .... I have not tried this feature, but it makes me think that the camera itself processes the noise reduction using the matching dark frame and it has already been accomplished when downloaded to the computer .... I do not find anywhere in the menu where it can be disabled on this camera. Jerry in Houston
