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easy way to despeckle an image

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  #1  
Old 07-05-2014, 04:02 PM
Caravaggio Caravaggio is offline
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easy way to despeckle an image

Hi,

I'm looking for a technique to despeckle an image that produces acceptable results. I've been using dust and scratches filter and then selectively painting with white on a hide all mask over the spots but don't want to spend the time. Are there any plugins that would do the job or techniques? The attached screenshot is at 200% view. The spots in the screenshot are in hair and on a woman's dress as I realize that it is probably hard to tell what the image is. Thanks.
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File Type: jpg retouchpro_screenshot.jpg (97.0 KB, 73 views)
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Old 07-05-2014, 04:25 PM
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philbach philbach is offline
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Re: easy way to despeckle an image

Well Sometimes you can get by with copying the layer and use darken blending mode. Then on the copied layer use the move tool and move the layer up a few pixels using the arrow tool and off to the side.

Another way that you can try is to use a threshold adjustment layer and dial it to about 40. Use the resultant spotted photo as an alpha channel and select the white spots and fill the selection with a sampled, suitable color.

A third way is to use calculations which some use to create a mask.
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Old 07-05-2014, 05:01 PM
Caravaggio Caravaggio is offline
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Re: easy way to despeckle an image

Thanks Philbach. I tried moving the copied layer a few pixels and putting it on darken and that worked in places. Great tip! I can see method 2 possibly working as well. Using calculations is probably beyond my abilities at this point. I'm curious what other suggestions retouch pro members have.
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Old 07-05-2014, 05:25 PM
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Tony W Tony W is offline
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Re: easy way to despeckle an image

Another way is to create a mask of the offending pixels only and then fill them with the surrounding good pixels to blend in. Several ways to do this and I just tried a method to create the mask using Minimum and Maximum filters and Difference mode to create the mask and a clipping levels layer to blend the result.

This method I have used in the past to remove salt and pepper dots on images and when the mask is created properly the effect extends to the damaged areas only. The method is referred to as morphological opening or closing depending on light area or dark area blending.

EDIT: Just changed the image as I attached the wrong one
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File Type: jpg MorphologicalOpen.jpg (158.4 KB, 44 views)

Last edited by Tony W; 07-05-2014 at 05:56 PM. Reason: Changed image
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Old 07-05-2014, 09:28 PM
Caravaggio Caravaggio is offline
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Re: easy way to despeckle an image

Tony, Your result looks very good. I am not quite able to figure out how you did it from your screenshot. Is there somewhere I can go on the web to read more about morphological opening and closing technique or for a step by step on how you did it? Thanks.
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Old 07-06-2014, 09:32 AM
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Re: easy way to despeckle an image

Quote:
Originally Posted by Caravaggio View Post
Is there somewhere I can go on the web to read more about morphological opening and closing technique or for a step by step on how you did it?
I actually thought by naming the technique that you would find many examples - seems I was wrong. What comes up are statements like:
For example, the definition of a morphological opening of an image is an erosion followed by a dilation, using the same structuring element for both operations.

Usually followed by in depth discussion of what happens under the hood and a load of mathematical examples - sheesh!

So unable to find a practical tutorial a brief description of how I applied the technique in PS. Note that if you have Matlab or similar applications these transformations can be done there and may be even better? Also there are other methods to produce a similar mask effects e.g. using Find edges and massaging until a suitable mask is produced.

  • Duplicate the background layer. This will be the layer that we will work on to produce our mask and is a temporary layer.
  • On this layer goto Filter / Other/ Minimum and select the filter radius that removes the spots. This will vary depending on image but in this case I think I used a value of 2. This will remove the spots but also make the image look dark so it now needs to be reversed.
  • With the layer still selected go to Filter / Other / Maximum and apply exactly the same value as you did for the minimum. The image should now look a lot better but requires a mask so that changes will only be made to the artefacts areas.
  • Change the blending mode of the layer to Difference. You should now see your spots highlighted in white and the rest of the image area black or near to black. Go to channels and see which one offers the best in separation of real image to artefacts and copy that channel. In this case I decided red channel best.
  • Your copy channel will need some tweaking to give you a good solid black image with the spots highlighted in white. Using a levels adjustment is usually the easiest and needs to be pushed to black to hide areas that need no attention and white those areas that you want to change. You may need to paint on the mask with black to conceal any real image areas that show through. Now use Select All / Copy to put your new mask into the clipboard ready for the next step.
  • Back in the layers area turn of the duplicate layer and make a new copy of your background. On this new copy run a Gaussian blur selecting the radius that completely blends the white spots with the surrounding areas.
  • Now add a layer mask to this blurred layer and paste the mask you created earlier to the mask. Your image should now look very close to the original, warts and all!
  • Next add a levels adjustment layer clipped to the blurred image below. Now by moving the midtone slider you should be able to blend the spots in seamlessly with the original image.
EDIT: Added information. The technique works as well for black spots but you reverse the filter procedure i.e.start with the Maximum filter then apply the Minimum

Last edited by Tony W; 07-06-2014 at 09:49 AM.
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Old 07-06-2014, 09:51 AM
Caravaggio Caravaggio is offline
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Re: easy way to despeckle an image

Thank you, Tony. That is great! Can't wait to try it out. I had googled 'morphological opening and closing photoshop' and only mathematical stuff came up. I think you've invented a new technique.
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Old 07-06-2014, 09:55 AM
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Tony W Tony W is offline
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Re: easy way to despeckle an image

Hope it works out well for you. If you get stuck or instructions not clear just ask.

Wish I could claim this my original technique but it is probably as old as digital imaging and techniques for reducing noise. Someone somwhere at sometime showed me how to do this. I wish I could remember so I could give them the credit
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