Correct Image Distortion and Noise

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PSDTUTS Photoshop Wiki / Photoshop Tutorials / Correct Image Distortion and Noise Distortion and noise are unpleasant, but unavoidable facts of life when you work in Photoshop frequently or do a lot of photography. Thankfully there are a few ways to fix these problems.

Contents

[edit] Correcting Image Distortion

Straightening the Image

Often, an image that isn’t straight is the fault of a bad photographer, but luckily we can fix this “distortion” in Photoshop.

  1. Select the Ruler Tool, which is in the submenu beneath the Eyedropper Tool. You can alternatively access this tool using the keyboard shortcut I, then Shift+I to alternate until you reach it.
  2. Draw a line using a reference point that should be straight; for instance, if there’s a horizon in your image, draw a line with the Ruler Tool from one end of the horizon to the other.
  3. Go to the menu option Image > Rotate Canvas > Arbitrary. The value will already be automatically set thanks to the Ruler Tool, so click OK.
  4. You’ll now need to crop the image, since the rotation will have added extra white space.

Correcting Pincushion & Barrel Distortion

Pincushion and barrel distortion are two more types of common lens distortions. Pincushion is comparable to the Pinch distortion effect in Photoshop, while Barrel is more similar to the Punch effect.

  1. Select the Filter > Distort > Lens Correction filter.
  2. Ensure the Remove Distortion panel is selected
  3. Use the grid in the preview window to help you align the image, moving to the slider to the left to fix barrel distortion and to the right to fix pincushion distortion.
  4. You may need to crop the image to remove added white space.

Repairing Perspective Distortion

A perspective distortion occurs when an image appears to be “leaning” in a direction it shouldn’t be – for instance, a tower that looks like it’s leaning backwards.

  1. Select the Crop Tool (C), and make a selection around the whole image.
  2. Check the Perspective box in the Options Bar.
  3. Use the handles to move the crop shape so that its lines are parallel with the lines in the image that should be straight.
  4. Press Enter or click the tick button in the Options Bar to make the changes.

This can take some practice, so don’t be afraid of using Cmd/Ctrl+Z to undo and start over.

Correcting Vignette Distortion

Vignetting is when a lens causes the corners of a photograph to be too dark.

  1. Select the menu option Filters > Distort > Lens Correction.
  2. Turn off the grid using the checkbox at the bottom of the window.
  3. Play with the Amount and Midpoint sliders listed under the Vignette section until the corners are no longer dark. A good starting point for the Midpoint is +50.
  4. Before making the changes, ensure you haven’t made the corners too light in the process, a common mistake – you want them to be just as light as the rest of the image.

[edit] Correcting Image Noise

  1. Navigate to the menu option Filter > Noise > Reduce Noise.
  2. Zoom in to a level where you can easily observe the changes in noise as you experiment with the options provided.
  3. Set and experiment with each option until you’ve found the optimal balance. Descriptions of each option are below.
  4. Where one color channel bears most of the noise, you can tick Advanced and then Channel to adjust correction levels in each channel.

[edit] Reduce Noise Options

Strength determines how much Photoshop attempts to reduce noise, based on the severity of noise in the image.

Preserve Details determines how much Photoshop will avoid altering edges and textures. The more details are preserved, the less likely Photoshop can remove noise, so finding the balance between Strength and Preserve Details is essential.

Reduce Color Noise works by looking for sudden changes in color to an unlikely spectrum in small pixilated spots. The higher the value of this setting, the more color variance/noise is reduced.

Sharpen Details – since noise reduction naturally means a more blurred and less sharp image, hence the Preserve Details option, the Sharpen Details option tells Photoshop to automatically sharpen the image after noise reduction is applied.

Remove JPEG Artifacts looks for the telltale signs of low-quality JPEG compression and attempts to remove them.

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