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My camera is a Sony a6000. The picture is taken at f6.3, 1/1000, ISO 1600, 210mm.

Why is it grainy in the background and how do I fix it?

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    The sensor is APS-C size, right? That's not a bad image then. As someone who used a lot of ISO 1600 color film in the 1980s and 1990s I'm tempted to say "you don't know what grain is!" ;-) Another thing is that such grain doesn't have to be bad. It is less (or less visible) in the parts that matter here. Sometimes too much smoothing gives a pasty appearance to surfaces which grain prevents.
    – Peter - Reinstate Monica
    Sep 22, 2021 at 11:22
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    Honestly, the grain kinda makes this picture nicer.
    – T. Sar
    Sep 22, 2021 at 18:20
  • Do you perhaps have RAW image as well? Zooming in the noise shows stuff similar to Gabor filter, and I wonder whether this could be an artefact of image processing in the camera. It seems interesting that out of focus has essentially constant noise no matter brightness, while parts in focus have way less noise; and I wonder if camera tries to get entire image in focus and fails.
    – Zizy Archer
    Sep 23, 2021 at 8:52
  • I agree with @ZizyArcher, it looks like JPEG artifacts.
    – Davidmh
    Sep 23, 2021 at 13:59
  • @Peter-ReinstateMonica the size of the sensor is irrelevant for noise. What matters is the size of the pixels, which is only correlated with the sensor size.
    – Davidmh
    Sep 23, 2021 at 14:01

5 Answers 5

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why is it grainy in the background

You chose to limit the amount of light collected by the sensor to the point Poisson distribution noise has a noticeable effect.

Instead of shooting at ISO 1600, f/6.3, and 1/1000 you could probably have used something like ISO 400, f/4.5 , and 1/500. Your image would have been the same brightness, but you would have collected four times as much light and amplified both the signal and noise by one-fourth as much.

... how do I fixed (sic) it?

Stop pixel-peeping.

The image looks fine at normal display sizes. The noise is only apparent under high magnification.

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It's called "photon shot noise."

For a given intensity of light there is also a given amount of noise; and the noise component is equal to √(photons/time/area). So, with more light intensity/availability there is also more noise; but also a better SNR (signal to noise ratio), which results in a less noisy image (because the noise is buried under the signal).

E.g. 40,000 photons/time/area has a noise component of 200; and an SNR of 40000:200 (200:1). Whereas 1,000,000 photons/time/area has a noise component of 1000 and an SNR of 1,000,000:10000 (1000:1).

Many think that the ISO causes the noise, but it doesn't... using a higher ISO either reduces the noise (increases recorded SNR), or it makes little/no difference (ISO invariant cameras). In fact, you can record an image at a higher ISO in bright/strong light and end up with less noise than recording the same image in weaker light at a lower ISO (or no-worse at least).

There are many ways to fix it after the fact; but like most problems, it's best to avoid it in the first place if possible; and that means collecting more photons (light).

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  • This doesn't seem to fit. You should be getting quite a lot of photons in daylight so variance should be quite low. Additionally, you would expect higher variance in darker regions but this noise seems quite constant. Finally, noise pattern doesn't look like shot noise - though maybe it is plausible that automatic sharpening and jpeg compression could mangle shot noise in such a way.
    – Zizy Archer
    Sep 21, 2021 at 19:18
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    @ZizyArcher, the settings suggest an exposure value of ~ 12; so overcast/shade conditions... and that's probably significantly offset by the brighter flower petals (i.e. the green areas are probably closer to 8EV). If you look at the yellow flower petals the noise is quite low there; but it is much greater in the darker regions immediately to the left of them.
    – Steven Kersting
    Sep 21, 2021 at 19:42
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    "...and that means collecting more photons" The problem is that ISO 1600 will saturate if you try to do that, so the only way you can collect more usable photons is to lower the ISO. I think you're trying to push a misconception that's only half of a half-truth.
    – J...
    Sep 22, 2021 at 12:07
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    @MichaelC; every article I've ever read on the topic calls it shot noise, or photon shot noise... because the cause is the random nature of photon arrival. It does follow Poisson distribution characteristics though.
    – Steven Kersting
    Sep 22, 2021 at 13:29
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    @StevenKersting You're confusing shot noise with Johnson noise. Shot noise is only affected by the total number of integrated photons that comprise the image. Fast shutter with bright light and long shutter with low light produce the same shot noise. The longer exposure will produce more Johnson (thermal) noise, but at higher ISO you're also amplifying that noise, which, on balance, still ends up for the worse. Shooting at a high ISO puts an upper limit on the total number of photons you can collect before saturating, and so puts a lower limit on the total shot noise in the image.
    – J...
    Sep 22, 2021 at 13:34
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Using ISO1600 tells the camera to aim for 1/16th of the exposure it would need for a full quality image. If you want to get better results, you need more light (and then can lower the ISO). More light can be gotten by a wider aperture (at this scale and a good autofocus, you should certainly be able to go wider one or two stops while still having at least the bee reasonably sharp front to back), by slower shutter speed (for a fast-moving object, not necessarily a good idea) or by using extra light. A reflector may be good for one stop. Flashes can be tricky at 1/1000s but there may be workable options for them as well.

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    In practice, ISO1600 and above are borderline for getting goodout-of-camera results on the a6000 (also on the previous similar NEX models), especially if there are large darker areas in the image that we expect to look uniform (and given how green sensitive we are, the green background is probably physically much darker than we perceive it).
    – rackandboneman
    Sep 21, 2021 at 16:49
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    How does ISO 1600 equate to 1/16th of the optimal exposure? ISO 100 is 4 stops away, 8x more light (required). And that doesn't necessarily equate to "full quality" either... that relates to achieving maximum sensor saturation, and most of this image looks underexposed to me.
    – Steven Kersting
    Sep 21, 2021 at 18:33
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    @StevenKersting 4 stops is a factor of 16, not 8. ISO100 is base level ISO on the given camera so it relates to using the full available dynamic range of the sensor. Newer Sony Exmor sensors are ISO invariant, meaning that the utilising the full dynamic range of the sensor means you want the exposure of ISO100 as long as you don't blow highlights, and when you say "most of this image looks underexposed to me", the metering appears to already avoid blown highlights.
    – user98068
    Sep 21, 2021 at 18:54
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    @user98068; yup 16x, I made a mistake. You always want to use base ISO for maximum dynamic range (invariant or not); each stop of ISO increase is essentially one stop less DR. But that assumes there is enough light to reach sensor saturation (SS/Ap). If there isn't, then ISO invariance just means you can use whatever ISO you want (as long as you don't push it into clipping).
    – Steven Kersting
    Sep 21, 2021 at 19:51
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    @StevenKersting "If you want to get better results, you need more light" is pretty much what I start the actual advice with, so I don't really get what the problem with my answer is supposed to be.
    – user98068
    Sep 21, 2021 at 20:12
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I'll leave it to people smarter than me for exactly why it happens, but fixing it in post is often not too difficult.

In Photoshop, there are noise reduction routines, this from CameraRAW…

enter image description here

turning
enter image description here

into
enter image description here

Or from OnOne NoNoise AI, just at default settings
enter image description here

click for larger

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    I am not sure if it is caused by how you uploaded the images, but both denoised images you are showing here have quite ugly blocking and banding artifacts in the background. It is difficult to say for sure since you for some reason have uploaded the output from OnOne NoNoise at a different resolution, but it seems to be as if quite a lot of image details are removed as well. Noise should be prevented when taking the picture. Using a noise reduction algorithm later is just an emergency solution.
    – jarnbjo
    Sep 21, 2021 at 10:43
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    @jarnbjo - the images are simply screenshots, converted to jpg so they're small enough to upload here. This is obviously something that needs to be done to the original file, so the absolute quality of these examples is unimportant.
    – Tetsujin
    Sep 21, 2021 at 11:01
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I will attempt to explain how the grain you are seeing is a product of the settings of your shot, and try to keep it simple without photography jargon or math.

Your photo has the settings f6.3, 1/1000, ISO 1600, 210mm. And I think those are decent settings for the image you took. A bee moves fast so 1/1000 is fast enough to get a crisp enough image of its body (but not fast enough to capture the wings). Your aperture is a relatively small 6.3, and that is probably because the zoom lens you used has a max aperture of 6.3 when zoomed in to 210mm, but also good for ensuring the bee is in focus. It appears that the photo was taken in the shade or on a cloudy day, and so the aperture and shutter settings appear to be at the most optimal possible for letting the most light in, and under the natural lighting conditions they can't be changed to let any more light in (aperture probably can't get bigger on your zoom lens at 210mm (zoom lenses with bigger apertures are very expensive due to the quality of optics required), and the shutter can't be any slower or the bee would be blurry) and so the ISO has to be turned up to 1600 to expose the image optimally. Your camera is a 2014 model I presume, and 1600 ISO is a higher (higher is a relative term, read the next paragraph for explanation) ISO setting for that generation of cameras, and so the grain primarily comes from that setting.

The ISO setting in digital cameras changes the voltage on the camera sensor, making each pixel more sensitive to light. Noise is caused by a pixel being tripped by some photons, but not enough photons for the camera to resolve the correct color or brightness for that pixel. Each pixel is like a mouse trap. The lower the ISO the more firm the trap is set, like a mouse really has to bump it good for it to trigger. As the ISO increases the trap is more loosely set, like just walking by it and causing the ground to shake may cause it to trigger, not catching a mouse, or in the case of a pixel, not catching the most accurate color or luminosity value.

Each year, camera sensor technology, and the image rendering software in cameras, make noise less and less apparent, that is shooting at 1600 ISO on a 2012 camera has significantly more noise than shooting on a 2021 camera at 1600 ISO. So the noise to ISO relationship is very dependent on the camera (sensor) you are using.

You will always have noise with current digital cameras, how much is dependent on the exposure settings of the camera and the amount of light in the scene. If you can't get a bigger aperture, and you can't slow your shutter speed any more for the shot you are trying to get, than all you can do is increase ISO. You have to learn your camera and image editing software to figure out how much you can raise the ISO for different types of shots. I usually use the lowest ISO possible for the required exposure (often I under expose a bit because I don't want to increase the ISO/noise, but instead edit the photo afterwards back to desired exposure resulting in the desired amount of light in the photo but less noise due to the lower ISO setting (I usually do this with my older noisier cameras)), that is I set the aperture and shutter first. But really noise is only a problem if it affects the fidelity of the shot or your desired artistic vision of your shot.

Back to your shot... it is about as good as you can get in terms of image fidelity with that camera set up. "Removing" noise from that shot in particular would be very easy for software, as it is all one color in the background and out of focus. Look up noise reduction software tools. They are available in most photo editors. Knowing how to edit noise will allow you envision shots that you normally couldn't take, like astro shots. And sometimes a shot is impossible to do with natural lighting conditions and camera noise, but you can invent your own source of light (like a flash setup) to take images that people have never seen before!

The best thing to do is to learn your camera. Try taking the same photo with two settings locked (say aperture and shutter), and change only one of them from high to low (say ISO). You will be able to learn how each setting works independently.

Cheers!

P.S. if you record photos in JPEG mode, the camera will denoise your photos a bit as part of rendering the JPEGs. This is not to suggest that you record in JPEG, but to explain that if you record in RAW format you have to render the photo yourself and denoise it and adjust color with a photo editor. RAW formats (.arw for Sony) give you the most control of the final image and how denoising is applied. Personally I use Adobe Lightroom Classic, but also there is RawTherapee, which is a decent way to enter into the raw editing realm for free.

Aperture Size Chart for Quick reference: enter image description here

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