Is visible red/chroma noise at low ISO on a Canon 200D a sensor fault?

Question

I’m seeing colored noise, especially red speckles, in dark areas and sometimes in blue sky images from my Canon EOS 200D / Rebel SL2, even at low ISO. The effect is most obvious when zooming in heavily on RAW files.

Does this indicate a hardware problem with the sensor, or is this normal image noise? If it’s normal, what should I do to reduce it when processing RAW files?

user81735 · Accepted Answer

No, this is not a problem.

I see red noise. I see green noise. I see blue noise.

That's not a surprise because there are three main colors in the Bayer filter, and the pixels beneath all of those three main colors are noisy.

The red and green noise are however more prominent, because the image is blue.

This noise is called chroma (chrominance) noise, as opposed to luma (luminance) noise.

You need to take a look at various noise reduction algorithms. Chances are your camera has already one for JPEG files but it won't be used for RAW files.

For RAW files, you can use the noise reduction algorithms of RawTherapee. Darktable too has some noise reduction algorithms, but I have found them to be much poorer than the ones in RawTherapee.

When you turn on noise reduction in RawTherapee, it should remove chroma noise effectively. To remove luma noise, there is an adjustable slider.

If you want less noise, consider using ISO 100 which is slightly less noisy than ISO 200. You could also consider switching to a camera that has Sony Exmor sensor which is somewhat less noisy than Canon sensors, but that would be expensive if you have already invested lot of money into Canon. You could also consider a full frame camera (or a full frame camera with Exmor sensor), but that would be even more expensive.

Typically there is less noise when:

The sensor is big (full frame)
The sensor is good (Sony Exmor)
The ISO level is low and thus exposure is higher¹
Noise reduction algorithms are used

_{¹ ISO actually has very little influence on the amount of noise in an image. It is the lower amounts of exposure we use with higher ISO settings that does that. If we shoot the same scene at [ISO 100, f/2.8, 1/30] and at [ISO 1600, f/2.8, 1/500] the difference in noise isn't because we used ISO 1600, it is because we exposed for 1/16th as long and thus allowed 1/16th as much light into the camera. Please see What are the advantages and disadvantages of using auto ISO on a DSLR? and Why would using higher ISO and faster shutter speed yield more noise than using lower ISO and slower shutter speed? for more.}

Is visible red/chroma noise at low ISO on a Canon 200D a sensor fault?

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