Incense

by Bart Arondson

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Sometimes shooting a long exposure results in hot pixels and some times dust on lens becomes apparent if shooting with very small aperture.

Despite having all good qualities the photo looks ugly due to these. I use Canon DPP for post-processing, which works at some extents and removes hot pixels, but if hot pixels are too big then DPP fails.

Attaching an example of dust on lens. There are 4 places (in sky area) where we can notice dust.

Johor-Singapore Casueway

I really don't like using Photoshop for post processing but it becomes necessary in these scenarios.

Please let me know if these is any good tool/tutorial for dust or hot pixel removal.

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My trained eye sees eight places in the image where there is noticable dust. –  Guffa Jan 4 '13 at 10:39
    
@guffa did I miss any spots on my cleaning procedures? :) –  Michael Nielsen Jan 4 '13 at 10:43
    
@MichaelNielsen: Yes one of the eight I counted, but it's hard to say if it's really a dust speck without seeing the full size image. –  Guffa Jan 4 '13 at 12:45

4 Answers 4

The dust is on the sensor, not the lens.

The light ending up in one place on the sensor doesn't pass through one point on the front lens element, it passes through the entire front lens element and is focused to one point on the sensor. You can actually cover a large part of the lens, or even shatter the front lens element, and still barely see any effect at all. That's why you still get a full picture in a mirror lens, and not a black circle in the middle.

To remove sensor dust in the image, you can use the healing brush or clone brush. Make the brush slightly larger than the dust speck, and clone from a similar area. It's mostly in an even area like the sky that you even see the dust, so it's often quite easy to remove.

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Hi Guffa, Later some other day, I cleaned the lens and took another shot, with same setting, (F22, ISO 100, Exp 30 Secs), those spot visible on the photograph were gone. Is it possible that dust on sensor was gone by it self? –  Pawan Jan 4 '13 at 10:06
    
@Pawan: Yes, that's possible, and it has to be the explanation. The 1000D has a self cleaning low-pass filter, which can remove some dust. –  Guffa Jan 4 '13 at 10:23

Are you able to state your model?

As you have said, dust can occur in the lens too. Cleaning either the sensor or lens can be difficult but using a simple blower on the sensor and both ends of the lens. If the doesn't get rid of the dust, I'd suggest to get off cleaned properly by the vendor or authorised service repair agent.

As for hot pixels, most cameras have a Pixel Mapping feature on them. Try looking through the menu. Otherwise state your model/make (I assume it's a Canon?) and I may be able to help you further if you need it.

EDIT: I'm on my mobile and can't see the picture in enough details. I assumed you were asking for future reference. Although my answer doesn't directly solve your current issue, I believe it is helpful for preventative measures.

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Hi BBKing I use "Canon EOS 1000D" :P –  Pawan Jan 4 '13 at 10:01
    
Sure BBKing, I will take care of this in future... cheers –  Pawan Jan 4 '13 at 10:12

The dust spots are likely to be dust on your sensor. Ideally, you would want (by order or preference):

  1. keep the sensor clean. Get a cleaning kit or get it serviced. Check also your camera's features, maybe it has automatic sensor cleaning built-in.
  2. if you can't or didn't, gather Dust Delete Data on your camera. Canon cameras will let you capture "Dust Delete Data" in order to record the dust spots locations and let you remove them through DPP. Follow this tutorial from the canon web site for a video demo of how to do this.
  3. if you can't or didn't, then you can try the spot removal/stamp tool in DPP

Edit: incorporated my comments back into the main answer

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Thanks matt.nguyen, my problem is removing dust after taking photo... some times we just miss cleaning lenses before taking photo, my sensor is clean though. –  Pawan Jan 4 '13 at 9:23
    
@Pawan it's not the lens that you need to clean to remove the dust, it's the sensor. And I did give that option as the first one because that's how I think you should do: 1. keep the sensor clean 2. if you can't or didn't, gather Dust Delete Data on your camera 3. if you can't or didn't, then you can try the spot removal/stamp tool in DPP. –  matt.nguyen Jan 4 '13 at 9:52
    
Hi Matt, later some other day, I cleaned the lens and took another shot. those spot visible on the photograph were gone. –  Pawan Jan 4 '13 at 10:01
    
To see if you really have dust on the sensor, take a picture of a white background, at a very small aperture. It should show what's on the sensor. Does your camera have automatic dust cleaning capabilities? It's also possible that the dust spot moved in between... –  matt.nguyen Jan 4 '13 at 10:14
    
Yes the camera have the automatic dust cleaning capabilities... and thanks for tip to find dust on sensor.. :).. cheers –  Pawan Jan 4 '13 at 10:18

The dust can be deleted after the fact with the clone tool. My program does it with a degree of blending, which yields better results than fully opaque cloning (the trick to good retouching, cloning, etc is to not overdo it). If you use Photoshop you can achieve this by fixing it in the a overlay layer and adjusting transparency.

Here I did a quick and dirty job, with a few mouse clicks around the dust areas:

Cloned Dust

This method can be used whenever the dust is on smooth/replicated areas.

If you cant find a place to clone, you need to apply an effects layer, and brighten the spot, and might have to adjust the colors, too.

Edit: I couldn't resist to test my thesis, and here is the result with the selective brighten method. I didn't have to adjust the colors:

Brighten

In my program this is done by adjusting the curves to make it brighter (doesn't have to be accurate, just not too little), and "painting" a blend layer with a "Gaussian paintbrush" to make a smooth transition. If it gets too bright, simply "blend" it back with the original a notch. In Photoshop you can do the same the layers, and the dodge tool.

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