Sometimes, particularly when taking a photograph at a high ISO, the image can become "grainy" or "noisy." Noise is an unwanted random texture in the image. In film, graininess is the result of using film stocks which contain larger, more sensitive, clumps of silver: hence the grainy appearance. In a digital camera, noise is the result of signal amplification: raising the ISO causes the the processor to multiply the output of your image sensor, multiplying the underlying electronic signal noise in the sensor and the camera's circuitry in the process.
Noise can add to a photo, but often it’s a pain and we’d like to get rid of it. Adobe Photoshop comes with a tool called ‘Reduce Noise’. In this tutorial, we’ll look at this particular filter and its effectiveness. It's important to point out that I'm working on a high resolution image. If you're editing a smaller image then the effects of the sliders on the filter will be increased. Just adjust accordingly.
1. Select Your Background
Firstly, open up your image:
You’ll notice my example (Spotto the owl for those interested) includes a lot of grain. I’ve chosen a subject where you can see both subject and the background clearly to make it easier to demonstrate the filter.
Once you’ve opened up the image, I’d suggest selecting your background separately with the lasso tool (draw roughly around it) as it’s best to treat your background and subject separately with this filter.
You can see I’ve included some of the owl where blur has occurred due to narrow depth of field as I want the filter to remove the noise from here in the same way as the background.
2. Set Reduce Noise Filter Options
At the moment I have options like this:
I’ve got them all set to 0% at so I can briefly go through each option and tell you what it does. That way you’ll be able to judge its effect on your image better, even without the preview window to the left.
- Strength: This is pretty straightforward, it’s the amount that the noise is going to be reduced. You’ll notice an advanced option (next to basic) which allows you to choose to reduce noise just in a particular colour channel. We’ll stick with basic for this tutorial though. You’re going to want to pick a strength that best suits your picture. If there’s a lot of detail (buildings or people for example) then you’ll want to go easy on this as it’ll take away a lot of the clarity. As this background is basically coloured blur, I’m going to slide this option up to full strength:
You can see this is looking a bit smoother. Note: you can click and hold inside the preview box to see the before/after.
- Preserve details: This comes into play when you have something with edges that you want to be crisp or details that you want to keep. More about this later.
- Reduce colour noise: This removes coloured pixels that can sometimes occur in JPEG photos, like when you get purple or green fringing. I don’t have that problem with this image, so I’ll leave that at 0%.
- Sharpen Details: Back to having stuff that you want keeping crisp. We’ll cover this when it comes to tackling our foreground.
- Remove JPEG artefact: Again not a problem here but this refers to the ‘blockiness’ that you sometimes get when you’ve saved something as a JPEG due to compression.
3. Select Your Foreground
So now we’ll move onto our foreground. Using the lasso tool as before, this time select your foreground and leave the background out:
The strength is still good at 10 (all the way up), as it doesn’t take too much detail out of my subject with this being a hi-res image. When I get to the preserve detailsfilter though you can really see its effect:
This is a comparison on the eye at 100%. The one on the left is has the slider set at 0% and the one on the right, 100%. You can see that by preserving details, the downside is that you get much more noise; the thing you’re trying to reduce!
The same sort of thing happens with sharpen details. If I was to use both options at 100%, I’d end up with this:
This looks worse than when I started! Generally for this reason, I tend to stick to a very low percentage (if any) for preserve details (less than 10% and remember that's for hi-res images) and leave sharpen at 0%. If you want to sharpen an image, Photoshop has better tools for the job anyway, such as the unsharp mask.
Results
You can see from the example that the noise is slightly less pronounced on the right-hand image; not much but enough to make a tremendous difference when viewed in full:
The background is definitely smoother and cleaner than the ‘before’ image we started with. When using this technique you might want to run it more than once on the background to smooth it out further.
Recap
This filter is never going to rescue a picture and it’s not designed to do that. Making changes to a photograph usually impacts on something else, in this case, clarity. If you run this over a full image to try and get rid of any grain then you’re going to end up with a picture that looks blurry or hazy. Used correctly and subtly though, this can effectively tone down excess grain and make a photo more pleasing. This tool also offers a good trade-off between effectiveness and control: it allows you to process selectively in a fairly quick manner.
Whatever process you use to reduce noise in your images, it's important to remember that reducing noise is just that: reduction. All photographs contain noise. When selecting a tool or approach, consider how much noise is an acceptable level for your purpose. Though this tool might not be the most powerful one in your kit, for some purposes it might be just right.
