60 Seconds

Removing Moiré Patterns

Tuesday March 6, 2001

Learn 3 ways to remove the unwanted dot pattern after scanning
from a printed image from a newspaper, book or magazine.

[ PSP index ] [ Composite Index ] [ PSP Links ] [ 3D Bits n Pieces ] [ Tutorial CD ]

What is a Moiré pattern? What causes it in scanned images? How to get rid of it in PSP7.

The answers to these questions make up the body of today's tutorial.

Moiré: (mwah ray) Having a watered or wavy pattern as certain fabrics, stamps or metal surfaces. -Webster-

For digital artists, a Moiré pattern is basically an undesirable pattern in an image, also referred to as an interference pattern. The physical nature of Moiré lies in interference of two or more regular structures with different spatial frequencies.

In real life if you go past two fences located one behind other or when you look at folded silk stockings, you will see moiré patterns.

Scanning halftoned art, or anything that has already been screened and printed such as pictures from a magazine, book or newspaper, produces Moiré patterns most often.

NOTE: Images in magazines and book are almost always copyrighted, be careful using images you didn't create in your work!

Today, in an extreme example, an old newspaper clipping from 1969, we explore three ways to rid a scan of a Moire pattern.

1. Using Paint Shop Pro's Remove Moire Pattern Filter.
2. Using a Gaussian Blur
3. Using the Noise >Salt and Pepper Filter plus a Blur>Average Filter

Newspapers images are the very worst to scan and repair, in my opinion, but they provide an excellent example for Moire. Newspaper images are low res images printed on low quality paper. :)

In building Web sites, clients often give me Xerox copies of photos or newspaper clippings or bad scans of line art and expect me to make them presentable again.

Method 1: PSP 7's Remove Moire Pattern Filter

On the left , a snippet of a larger image, shows how awful a moire pattern can be.

Notice the dot pattern throughout the image.

To do this tutorial, click on the image to open the Originalimage.jpg and then right click to save to your hard drive. You can work on the full image during this tutorial although for space sake I use snippets like the one on the left.

Open the large image in PSP7, then Save a copy of the image as Originalimage.psp in the PSP format. We will use the original 3 times.

From prior experience, I have found that scanning at 4 times larger than the end result will be works reliably well. More pixels to work with. The working image is 1700 pixels by 1089 pixels so my final image will be about 425 x 250 or so.

Go to PSP's Menu bar and click on Effects, Enhance Photo then Remove Moire Pattern from the flyout boxes. See below.

Time to fiddle with settings.

Notice in the screen shot on the left what the various settings result in.

At a setting of 1, there is still a lot of grain. Even with settings of 3 and 5, the image contains some residual patterning

Our mission here is to sufficiently blur the image out of its Moire pattern and by adjusting the settings, a Fine Details of 7 appears to be the best for this job.

Click OK to apply the filter.

Applied snippet of the image at 1 to 1 zoom, notice how the dot pattern has disappeared.

Yes now its really blurry.

Let's finish this one up.

On the Menu Bar, select Image >Resize.. On the dialog box set the percent to 25 and click OK.

Notice how much cleaner it looks even though blurry.

Put back some detail with a bit of Unsharpening.

Go to PSP's Menu bar and click on Effects > Sharpen > Unsharp Mask...

On the dialog box, set the Radius to 1, Strength to 100, Clipping to 2 and press OK. Note the result below.


Save the image at this point in the JPEG format.

Method 2: Using a Gaussian Blur
(This works in PSP6 as well)

 

Open the copy you made in the beginning of Originalimage.

Go to PSP's Menu bar and click on Image > Resize...

Click the radio box for Percent and enter 25 percent. Press OK.

Notice how much better the image looks already. Resizing down hide image flaws!

Still you can see the graininess in the image.

 

 

On the Menu Bar, select Effects > Blur >Gaussian blur.

Set the radius to to .5 pixels.

Press OK.

Notice how the grain is smoothed out.

Then to regain some of the sharpness, go to PSP's Menu bar and click on Effects>Sharpen>Unsharp Mask and set to: Radius 1, Strength 33 and Clipping 1.

The results are quite good!

So ends the second Gaussian Blur method.

Export the image as a JPEG at this point and close the original without saving.

Method 3 : Salt and Pepper and Blur Average

 

Open the copy of Originalmage you made at the beginning.

On the Menu Bar, select Effects > Noise > Salt and Pepper...

On the dialog box, set the Speck size to 3 and Sensitivity to 4.

Check both Include all lower speck sizes and Aggressive Action boxes.

Press OK.

There is still a pattern visible in this 1:1 zoomed snippet but its not the same as the original dot pattern.

Sort of has an artsy effect.

Next go to PSP's Menu bar and click on Effects> Blur > Average...

Set the filter aperture to 7.

Press OK.

Again notice how the grain disappears leaving the image blurry.

From the Menu bar do a Color > Adjust > Brightness /Contrast... with the Brightness set to 8 and the contrast to 15.

Press OK.

Brightness and Contrast perks up the image a little.

Then go the Menu bar and select Image and Resize and use 25 percent again.

Finally from the Menu Bar select Effects > Sharpen > Unsharp Mask with the radius of 1.00 Strength of 50 and Clipping of 0.

The results are quite good!

Export again as JPEG.

Recap:

Pick your method!

1. Moire Pattern Removal Filter
2. Gaussian Blur
3. Salt and Pepper, Blur Average Filters

Compare the results below. 3 Ways to accomplish basically the same thing.

Throughout all the methods, you probably noticed that each filter blurred the image. That's probably the main key to removing Moiré patterns. From there resize down a lot and add some sharpening to restore some detail. Resizing down a lot helps remove the pattern as well.

Other goodies to futz with these images.

After correcting the Moiré pattern, try converting the image to greyscale by going to Colors on the Menu Bar and picking Greyscale from the flyout box. This removes any color anomalies, such as the yellowing effect.

If you like the aged look, return the image to 24 bit color by going to Colors on the Menu Bar and Increase Color depth and 16 Million colors from the flyout boxes. The image will return to 24 bit color but it really only contains 256 colors at the moment.

Re-color it by going to Color again on the Menu Bar and Colorize... Set the colors to Hue 24, Saturation 50. Voila aged again. But with only 256 colors. Now export as a GIF image! See below.

That's it for this week, Folks.


[ PSP index ] [ Composite Index ] [ PSP Links ] [ 3D Bits n Pieces ] [ Tutorial CD ]

All Tutorials and Tips including images and text
Copyright 2003 3D Workshop, Inc.

Further distribution prohibited without express permission.
For information e-mail is in image below