SD1 Pattern Noise

Started May 4, 2012 | Discussions thread
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jbr
jbr
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SD1 Pattern Noise
May 4, 2012

It appears the SD1M has two banding and pattern type noise components that may show up under certain circumstances. The vertical pattern noise is what many have noticed in skies that have been pushed a bit and shows up as vertical light/dark lines. The interesting and bothersome nature of this noise is that it will show up in ALL images if pushed enough, even if the image is perfectly exposed. This pattern noise is fixed and shows up in the same place and intensity from one image capture to the next. However, this vertical pattern noise only mainly effects the higher intensities that are captured by the sensor and largely disappears as intensity decreases and is replaced with a more random banding type noise that shows up in poorly exposed areas. In order to illustrate I will use the following image of a couple of icebergs:
SPP Noise at 0,0, Sharpening at -2

The image is fine (a bit boring due to flat light) as is and you cant really see any pattern noise in the sky, so all seems ok. However, if you push the contrast using curves in PS the image starts to get a bit more interesting. But when this is done the pattern noise starts to show up. I have added more contrast to a selected section to make the noise easier to see.
SPP Noise at 0,0, Sharpening at -2, PS USM

And if that is not clear enough here is a crop

So what does this noise actually look like? It's pretty ugly. Here is an image created from the average of 5 captures of a flat white page. The images were High Pass Filtered prior to averaging to remove unevenness due to lighting. The contrast has been bumped in the image so the pattern is visible.

This pattern is so consistent over time that it may be used to reduce the appearance of pattern noise in images taken weeks apart. Here is the same image with the pattern noise subtracted in PS using a difference layer.
SPP Noise at 0,0, Sharpening at -2, PS USM

and a crop

So, I believe this fixed pattern noise is the cause of what many have seen in the skies when pushed a bit. This is not the noise that is seen in the poorly exposed areas.

A few notes and conclusions to this point(in random order):

1. It may be difficult to increase contrast in sky areas (and other flat well exposed areas) of an image without showing this noise.

2. The noise is in the raw data. I used Roland Karlsson's x3ftools to look at the raw data and the pattern noise is there so it it not a processing artifact.

3. I have had two SD1M cameras and both exhibited the same type of noise - but a different pattern.

4. The processing in SPP changes the noise characteristic but it does not remove it. So, if you want to remove the noise using the technique I have shown you have to process the reference image the same as the subject image.

5. The noise is identical on RGB channels so you can use a monochrome reference and achieve the same results as used here.
6. This may very well be a sensor problem and is in all SD1 cameras.

7. The process of subtracting a noise signal from the image may add noise and hide the pattern that was. In this case with the average of 5 frames for the noise reference the standard deviation of the noise was actually reduced due to the removal of the pattern noise.

8. Not sure this can be automated and maybe thats why Sigma has not added this to the processing chain. However, as SPP alters the noise pattern then it has to be fixed in the camera or SPP as doing in post conversion is a pain in the ass.

9. Maybe I am getting too picky as the image presented here is not that bad but after using the SD14 for 4 years and getting silky smooth skies that show no hint of this I think this has to be dealt with and to me it is the biggest problem right now with the SD1M.

Joe

Sigma SD1 Sigma SD14
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