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I've been trying to reduce the noise for the clouds image using noise>reduce noise but even though I've been doing it multiple times this strange line in clouds appears. It becomes more apparent when I have adjustments layers active.

enter image description here enter image description here

Any tips how to make the clouds look more smooth?

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    That’s not technically noise so reduce noise won’t help. Have you tried just blurring the affected area? – Westside Feb 12 '18 at 12:20
  • hello lucas131, welcome to GDSE. Please include your attempts into your question, and please post your images in there as well. Lots of users--myself included--aren't willing to click a shortened link, because of the risk of spam. You can always edit your question by clicking the edit link right under it (or even those two I just posted). If you have any questions, please have a look at the tour and the help, they should tell you how this site works. Thanks for understanding. – Vincent Feb 12 '18 at 12:30
  • That doesn't look like noise to me. It looks more like the result of overly aggressive noise reduction. This is often found in images from cameras with small sensors, such as point and shoots and mobile phones. – Billy Kerr Feb 12 '18 at 12:51
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The lines you see in your image are called banding.

An image doesn't only have a resolution when it comes to its dimensions. It also has a bit depth which can be seen as the "resolution" of the color values. Banding occurs when this "resolution" forces the steps between colors to be so large that the image cannot create the illusion of a smooth gradient.

8-bit, No banding Indexed, Banding

This can happen if an image has a low bit depth (like an image in Indexed mode, a gif or png), or if you manipulate an ordinary (8-bit and more) image further than its bit depth allows. You "stretch out" color data at a certain "resolution" to have a larger span and a kind of "pixelated" effect occurs. Much like what happens if you scale an image up, but with the colors instead of the dimensions.

Sometimes I've had banding problems using some of Photoshop's adjustment layers and found that I could achieve what I wanted using a similar tool. For example Hue/Saturation where I used Channel Mixer instead and the problem disappeared.

In your case you need to either remove/change the adjustments that cause the issue or smooth out the colors of the banded layer by somehow adding some data where it's missing. The two basic tools for that is:

  • Gaussian Blur (or other kinds of blur) - adds the missing transition between colors but removes some details.

  • Noise (any kind that works) - camouflages the banding and adds fake details.

Experiment with applying these effects (maybe multiple times) with different settings and in different order. (I would turn the image into a Smart Object to make it easier.)

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Maybe Topaz DeNoise could help? This is example of it:

enter image description here

After zoom it looks much better.

Topaz is a plugin with many different options to help with photo-editing, like denoising, "clearing" images, or adjusting colour filters. You can download trial version here => http://www.topazlabs.com/

For your problem, I used DeNoise plugin, which is most preferable for that kind of "smoothing" things.

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The reason is already explained in comments. Agressive noise reduction in a smartphone camera (or another with small sensor) has made it. Maybe you have increased it by applying more noise reduction. Alternatively your image would be full of colored noise. Now it's smoothed (the remnants are still visible as large colored areas), but the edges in the image are guessed and restored. Unfortunately the cloud didn't have edges, the noise reduction program in the camera has guessed wrong.

If you have added N.R. then your program had guessed right because the edges were born in the camera.

Make a selection that covers the cloud. Leave a little safety margin at the image edges and the statue. Then add Gaussian Blur. Here's an example. The used selection has been left visible in the screenshot.

enter image description here

The selection: select all or a rectangular area. Use the quick selection tool holding Alt key to get the statue out of the selection. Contract the selection few pixels.

There's still some false coloring in the cloud. You can get rid of it followingly

  • select the statue as exactly as possible; draw a path or use the polygonal lasso tool. Quick selection tool - altough used here - is too coarse.
  • inverse the selection, desaturate
  • goto Image > Adjustments > Hue/saturation > Colorize, adjust hue, saturation and lightness sliders for original cloud color and brightness
  • contract the selection 5 pixels
  • add 5 pix gaussian blur

The result:

enter image description here

There's still some enbankment (=banding) in the cloud. That's because 8bit/color cannot make smoother gradients. The defect can be masked by adding about 1% noise. Do it without killing the selection, the statue doesn't need the noise. The result:

enter image description here

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