Recently all the photos taken with my digital SLR have white spots at two specific places. A friend suggested that it’s caused by dead pixels and would require repairs by a service centre. Can’t I get rid of them by cleaning the sensor? I do see a lot of coloured spots in JPEGs made during night photography, but I guess that’s a different problem. How would I solve that?
It’s possible that a dried drop of liquid on the sensor is causing the dots, M.K.F., but not likely dust specks since those would appear as black dots. You could send the camera to a service centre—as recommended by the manufacturer—or consider cleaning the sensor yourself with one of the products from Visible Dust such as one of the swabs plus the SensorClean liquid. (VisibleDust is a U.S. company, but many Canadian retailers sell their cleaners.) But take maximum care not to scratch the sensor; follow the accessory manufacturer’s instructions to the letter!
If the two specks still appear in your photos after the cleaning, then your friend is right. The sensor has some dead or stuck pixels: photosensitive dots that can no longer function. A few cameras offer a menu item to solve that problem, such as Pixel Mapping; if yours does, activate that feature as discussed in the owner’s manual to eliminate the dead pixels. Otherwise, you would need to send the camera to a service centre for an inspection and expensive repairs…or simply clone out the spots (when they are obvious in images) with software.
The colourful speckles (or graininess) that you see in night photos—made at high ISO or during very long exposures—are an entirely different matter, as you suggested. Those are simply evidence of digital noise. If you find the digital noise pattern to be objectionable, set the Noise Reduction feature to a higher level. Or use the Noise Reduction utility in your RAW converter or other imaging software. For additional insights on this topic, read this previous Q&A item: What is the simplest way to minimize digital noise at high ISO levels?