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I recently noticed some weird discolored specks in my images, and I thought it was a lens issue, so I tried cleaning the lens. The specks got a tiny bit smaller, but unfortunately still there.

I took two pictures of a wall (apologies for awful quality), before and after the cleaning.

Before (zoomed way in): enter image description here

After (zoomed way in, same location): enter image description here

I'm pretty new to photography, so I didn't find anything dust related. I thought it could be sensor damage, but I've never taken direct images of the sun and I don't take outdoor pictures much either.

How can I fix this? Any help is appreciated, thanks!

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  • \$\begingroup\$ Try another lens? It looks like a hot pixel (to some extent a normal thing) or possibly a problem with the lens coating / cleanliness. A different lens completely is the best way to say lens vs camera. \$\endgroup\$
    – AthomSfere
    Sep 18, 2019 at 19:58
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    \$\begingroup\$ Possible duplicate of Why some pixels become hot pixels? \$\endgroup\$
    – OnBreak.
    Sep 18, 2019 at 20:01
  • \$\begingroup\$ @AthomSfere unfortunately i'm just starting and i don't have another lens :( \$\endgroup\$
    – zli
    Sep 18, 2019 at 20:06
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    \$\begingroup\$ I'm not convinced these are hot pixels. If your camera has an automatic sensor cleaning routine, run it a few times and then try your test again. Do the spots move? What happens when you use a wider aperture (using the same ISO and shifting the shutter time)? What happens when you use a narrower aperture? \$\endgroup\$
    – Michael C
    Sep 18, 2019 at 21:10
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    \$\begingroup\$ Unrelated but interesting: It's possible to use that sensor noise to identify the device that captured an image. Source Smartphone Identification Using Sensor Pattern Noise and Wavelet Transform \$\endgroup\$
    – rath
    Sep 19, 2019 at 11:08

3 Answers 3

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Looks like a hot pixel (the white pixel in the lower half of the picture is more conspicuous than the blue pixel in the upper half and will likely be green before demosaicing). Hot pixels tend to become more apparent with longer exposures. Basically a sensor deficiency, either temporarily or permanent.

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    \$\begingroup\$ thanks! what causes the sensor deficiency? is there a way to fix it? \$\endgroup\$
    – zli
    Sep 18, 2019 at 20:09
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    \$\begingroup\$ @zli Pushed enough, all sensors will show hot pixels. Longer exposures, high ISO, higher ambient temperatures, less signal (light), etc. will make them more noticeable. When shooting a bright scene, the hot pixels are usually lost in the abundant light falling on the sensor. When shooting in very low light or grossly underexposing, there's not enough light to drown out the hot pixels. It's covered at Hot, stuck, or dead pixels. What's the difference? and How to prevent hot pixels? \$\endgroup\$
    – Michael C
    Sep 18, 2019 at 21:06
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I ran a few more tests. Here are the results:

No change to sensor:

  1. f/2.8, 1/6", ISO 200
    • Blue specks (similar to the top speck in the sample pictures)
  2. f/10, 2.0", ISO 200
    • White specks (similar to the bottom speck in the sample pictures)

Manual sensor cleaning:

  1. f/2.8, 1/6", ISO 200
    • Blue specks in the exact same location, but smaller
  2. f/10, 1.8", ISO 200
    • White specks in the exact same location, but smaller

Pixel mapping:

  1. f/2.8, 1/7", ISO 200
    • as far as I can tell, nothing!
  2. f/10, 1.9", ISO 200
    • as far as I can tell, nothing!

I guess the pixel mapping solved it!

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    \$\begingroup\$ In future tests, cover up the lens (so you shoot blackness) and don't bother setting the aperture. The only things that matter are exposure time and ISO. \$\endgroup\$
    – Nayuki
    Sep 19, 2019 at 16:54
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Those are defective pixels, specifically "hot pixels", in your image sensor. It's rare for a sensor not to have one or two, unless you pay the big bucks for one that's been carefully inspected.

You usually don't see hot pixels in finished published works. Usually software at some level detects these and replaces those pixels with an average of the surrounding pixels, or a value determined by a more sophisticated algorithm. For some cameras, the hot pixels are found during testing at the factory and recorded in the camera's firmware. Then the images taken off the camera have those pixels automatically fixed in-camera.

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