Dead / Hot pixels on DSLR

[spacetrace]

Hello, Last night I was out taking long exposure of the night sky using my second hand DSLR Pentax k100d. I have noticed that taking long exposures +20 sec etc I see a lot of dead/hot pixels which ruins the entire image. I have noise reduction switched on which does improve the image but not enough to remove these dead pixels. Does anyone have any tips/ tricks on what I can do to remove these or get them fixed. I known the ccd chip needs cleaning as when I take daytime images of the sky then I clearly see a dark smudge that is dust on the chip. Is it likely that cleaning the ccd would improve the issue with the pixels or should I see if I can send then camera back to Pentax or specialist?

Thanks all

[steppenwolf]

The dust will not effect the hot pixels but it would be good to start off with a clean, dust-free sensor. You could try a high power 'puffer brush' WITH THE BRUSH REMOVED to try and remove the dust yourself but I would not recommend touching the sensor with any cleaning gear.

To help with the removal of hot pixels, you could try taking your own DARK Frames and subtracting these in your stacking software.

[spacetrace]

Good suggestion, never thought about doing it that way, only as I have only just started playing with stacking software.

[FraserClarke]

There is no way you can physically 'repair' the pixels. They are a feature of all CCD (and CMOS) chips. The more expensive the chip the fewer there are; but all CCDs have them to some extent.

The good news is that you can usually get rid of them pretty successfully with image processing. Dark frames as suggested are a very good starting point; that will clear up a lot. Also, when you combine together lots of images, there are routines which can say "this pixel is rubbish, I'm going to ignore it". Takes a bit of practice to get it all working well of course, but there is lots of advice on here. Doesn't sound like there is anything fundamentally wrong with your camera...

[roundycat]

there is a feature in my Olympus that allows you to 'repair' the chip by switching off the offending pixels. I'm not sure whether it simply returns all hot pixels to black or gives them an interpolated value based on nearest neighbour.

Good software will have a hot pixel removal filter and Photoshop Despeckle or Dust and scratches filters may help.

Dennis