The Cause: Sensor Noise

Each pixel in a camera sensor contains one or more light sensitive photodiodes which convert the incoming light (photons) into an electrical signal which is processed into the color value of the pixel in the final image. If the same pixel would be exposed several times by the same amount of light, the resulting color values would not be identical but have small statistical variations, called "noise". Even without incoming light, the electrical activity of the sensor itself will generate some signal, the equivalent of the background hiss of audio equipment which is switched on without playing any music. This additional signal is "noisy" because it varies per pixel (and over time) and increases with the temperature, and will add to the overall image noise. It is called the "noise floor". The output of a pixel has to be larger than the noise floor in order to be significant (i.e. to be distinguishable from noise).

Another type of noise, often referred to as "stuck pixels" or "hot pixels" noise, occurs with long exposures (1-2 seconds or more) and appears as a pattern of colored dots (slightly larger than a single pixel). As explained in the noise reduction topic, long exposure noise is much less visible in the latest digital cameras.

Dear all sifus, i wanna ask what is wrong with my camera. When i take photos using 8 secs shutter speed, i get blue and red dots.

while i take pictures above 1/4 sec shutter speeds, i dun get red and blue dots. What is the problem im having here? Any sifus can tell me mah?

All sifus.. is this the best i can do using photoshop cs2? Pls advice advice.. ty!
tools used are, noise reduce, dust and scratches, sharpen, and surface blur. Thanks!