Noise

March 03, 2016  •  Leave a Comment

CityscapeCityscape

Noise can creep into almost any image that is dark, like a nighttime shot, or one that has shadows. Noise can appear grainy in some areas and even have odd colors in the darkest areas. Pixel density on a camera sensor (many crowded into a small space),  smaller sensor sizes such as in a cell phone, High ISO, and long exposure times can all contribute to unwanted grain in an image. How much is too much? Some like the artistic look of a little grain, especially in a black and white image. However, most would agree when one can not see important details in an image, it is too noisy.

Most photographers understand the importance of shooting a well exposed image, but sometimes shadows will appear in some images and nighttime shots as above can be tricky at best to get a good exposure. Some photographers will also sharpen certain images during the editing process, which may only worsen the appearance of noise.

Consider the Cityscape image above. Some may want to sharpen areas of detail such as the buildings. But, looking at the sky, there is no detail so it makes little sense to sharpen the entire image. There is a relatively easy way to limit what may be sharpened without necessarily resorting to a complex Photoshop selection or layer masks.

During the editing process, many people will start with Lightroom or Adobe Camera  Raw. For what we area talking about in this post, the process will work exactly the same.  

  • Open a dark image or one with shadows
    • ​If you are using Camera Raw, select the detail panel (two triangles). This will have sharpening and noise reduction sliders.
    • If you use Lightroom, you will find the detail panel with your sharpening & noise reduction sliders in your develop module, typically on the right hand side of your screen.
  • ​Near the bottom of the sharpening panel, you will see a masking slider
    • Hold down the ALT (or Option) key at the same time you click directly on the mask slider (not the label).
    • You will see your image almost entirely white. This means that EVERYTHING in the image will be sharpened. (remember, there is no reason to sharpen the sky!)
    • Move the slider gradually to your right, and you will notice that portions of your image will turn from white to grey and eventually black. When a portion of the image is black, this means NO sharpening will occur.
  • You will likely want to move your luminance slider to the right to reduce noise. Don't overdo it, or your image may get fuzzy.

By using these quick and easy tips, you may find that you may not need to go much further in reducing noise in your image. One additional tip:

  • Consider working with a 16 bit image, rather than an eight bit image particularly when working with large areas of sky or nighttime images. You will have more colors to work with resulting in a better final product. 

 


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