Maybe 40 years from now we will look back and be putting noise into our images remembering it with the rose color fondness that film grain has and debating whether Nikon noise or Canon noise looked better.
What is Noise?
Just what is “Noise”? Where does it come from, how can we prevent it and how do we get rid of it if we can’t?
Noise is present in all electrical devices because well, simply nothing is perfect and through all the circuitry in devices there is always some trade off and some nasty by-products to everything, Noise being one of them. In our Digital images it shows up as circular points with some hard contrasty edges that take away from the smoothness of our image and can mask some of the important detail in our images if it becomes excessive.
Noise is always present, it’s just a matter of whether it is visible in normal viewing, which could be on-screen or in print. The point at which it becomes distracting may be up to the individual or the particular image or even how it is viewed.
Here is a typical noisy image that was both shot at high ISO and underexposed by about a stop
What makes noise visible?
Noise may become visible and an annoyance from a few different sources.
- ISO noise, the higher the ISO we use in our cameras, the more noise they generate. Cameras have gotten a lot better operating at higher ISOs without excessive noise but every camera has a threshold.
- Long Exposure Noise. When we do very long exposures, such as shooting Star Trails at night or long multiple minute exposes to fog water for that cotton candy effect or simply shoot in very low light. During those long exposures, the Digital Sensor produces heat which can also produce unpleasant noise.
- Under-exposing our images. When we underexpose our shots, it makes the noise in the shadow and midtone areas much more visible. Good exposures and quality light is essential to keep noise down. Some even “Expose to the right” or slightly overexpose images (without clipping) in order to later in processing bring back down the exposure and with it the noise level
- Excessive or aggressive Editing. Anytime we work on a pixel image and increase the luminance (lightness) or chrominance (Color) values in any way, we increase the visibility of noise. The more we do, the worse it usually gets, Even popular techniques like HDR can increase noise because in the tone mapping of those images, pixel values are raised in order to bring our shadow areas for more detail that may have been invisible in a non-HDR image. Even the popular Single Image HDR type processes which I love can introduce noise because it essentially is doing tone mapping and raising pixel values.
- JPEG Compression Noise. This is different than sensor noise and has a different look to it, more of a smearing and pixelization. This noise is harder to get rid or but actually may be easier to prevent with proper workflow.
What are some things we can do to prevent noise?
Low ISO First and foremost; we should try to shoot at the lowest ISO possible for our situation. If you can open up your aperture without affecting the DOF you are trying to achieve rather than increase ISO, do that. Slower shutter speeds that still stop the motion we may have or are within the speed that we can hand-hold without showing camera shake then do that. If you can’t handhold and are not shooting a moving object then consider using a tripod instead of raising the ISO.
Expose Correctly Secondly: Expose your scene correctly and as best you can. Underexposing will increase noise, so getting a correct or slightly over exposed image will make all the difference in the world. The best way to know is to check your histogram. If you see most of your histogram bunched up to the left and very few pixels or a big gap on the right, you probably are underexposed.
As I talked about earlier, some photographers like to “shoot to the right” which involves slightly over exposing their images and pushing the curve in the histogram more towards the right hand side. Just don’t go too far and clip your highlight because you may loose detail which can be worse then the noise you are trying to prevent. After someone has shot to the right, usually in post they will bring that luminance range down and take with it noise.
Edit with a light touch Watch your editing. If you have an image that is slightly noisy to begin with or even if you don’t, you can increase and exaggerate that noise by excessive editing and manipulating the lightness values and color values of your image. So try not to push Levels or Curves too far or even the saturation beyond what the image needs.
If you are taking some big swings to give an image Pop or Punch, then consider where in the process you are making those adjustments. If you shoot RAW rather than JPEGs you are at an advantage because in most case in a RAW editor that is not pixel editing you can push things further without some of the side effects you will get if you try to make those adjustments in a Pixel editing program.
Crop reasonably: Also watch how much you crop an image, if you crop too many pixels out of an image we essentially magnify the image and it may make the noise more visible in the image.
For JPEG compression noise, Always save files with the least amount of compression, (Photoshop 10+) or consider using a file format like Tiff or PSDs that are not subject to lossy compression noise.
For long exposure noise, consider turning on the long Exposure Noise Reduction available in the custom menu of better DSLRs.
Getting rid of noise that is there
Despite our best efforts and intentions, you WILL get noise at some point and enough of it that it needs our attention. The best way to deal with it is by a dedicated noise reduction program such as Topaz DeNoise 5
In getting rid of noise in our images we have to make some decisions and observations so that we don’t introduce any counter artifacts in the process such as softness in the image. My usual workflow would be to check for noise in the beginning of my editing process and take care of it in the beginning.
View at the size it will be seen
The most important thing we have to do though is consider how this image will be viewed to determine how much noise reduction we need to use. There are two areas of Post Processing that are totally dependant on this consideration. They are Noise Reduction and Sharpening.
If you have an image that will be seen at 600 x 400 pixels on a web page, that image will need much less noise reduction than an image that is being printed at 20’ x 30” or say 2650 x 1440 Screen wallpaper. Too often we find ourselves pixel peeping at 100, 200 or 300% and we will ALWAYS see noise at those magnifications and many times when we remove noise at those zooms, we actually will remove too much and loose a lot of detail in our images
So when making Noise reduction adjustments and judgments do so at 100% max or even better at the actual print size of screen resolution the image will be used. (For how to calibrate your monitor to show the actual size of a print see this article on Sharpening).
The final thing to think about is that noise is more visible in areas of little detail for the most part. Such as skies or large areas of a single color. Those areas are most often the areas that will also show banding from Aliasing/moiré in our images. In my sample image the noise was most visible in the sky areas
Using Topaz DeNoise 5
So knowing what we know above, using Topaz DeNoise 5 to remove noise really could not be any easier.
First before opening the Topaz DeNoise filter, I always make a duplicate layer or better yet, make the layer I want to work on, a Smart Object layer in Photoshop (ver.CS4, 5 & 6). The advantage of using a separate layer is that we haven’t destroyed any pixels, if we don’t like the results we can delete that layer and start over or even vary the opacity.
By using Topaz DeNoise – or any filter – as a smart object we have the option of returning to the filter screen and making changes if what we did the first time was not to our liking.
One we get into the DeNoise 5 screen we see it is set-up in what has become the de-regular panel screen. Presets left, preview image center, adjustments right. The image will open and then zoom to 100% you can zoom in further if you like but as I said earlier try not to and make sure after your adjustments you go back into Photoshop to make sure you have eliminate enough noise and not lost too much detail at your final image size.
To start off with the one single great thing about ALL topaz software is their presets. They are about the only company that gets them right. Real and usable presets that many times may not need any further adjustments.
For this image set to the 100% I chose the RAW Moderate Preset. You’ll notice that there are Jpeg Presets and RAW presets. The Jpeg presets are designed for Point and Shoot cameras and smaller image sizes. The RAW presets are for DSLRs and larger image sizes. You can use either on any file type (RAW, Tiff, PSD, Jpeg) it is more about the size of the sensor, image and the camera type.
Choosing RAW moderate got me most of the way to my goal but at this point I can tweak the settings a little further. The nice thing about the controls in DeNoise 5 is that we can work on color channels separately and also Highlights and Shadows separately. So knowing I wanted to eliminate the noise in the sky area ( Because it is most visible there) I upped the blue channel and the highlights channel and it effectively eliminated all the noise in those areas.
(Note for those CA Peeps, the small amount of CA visible was later removed in Lightroom)
I brought back in a little bit of detail by turning down the Blur control and adding just a bit of Grain.
Pressing OK brings me back into Photoshop and there I checked the image at the size I was going to print, 12” x 18” and it looked just fine, plenty of detail, no visible noise.
Here is that final image. For an image I wasn’t sure would work. It was shot late in the day under stormy skies so I needed ISO 1000 to get enough shutter speed to stop the moving locomotive. It made for a beautiful print with just a little touch of Topaz DeNoise 5
My closing thought is, I can’t stress enough viewing the image correctly at the size it will be seen. So many people pixel peep deep into the image and remove detail they don’t need to. Evey image has noise…every
Whether it is visable is the question
So there you have it, just about all I can scream over the noise
Hope that helps,