Removing large number of dust spots from 35 mm slide scans

[Bill Junk]

I'm wondering if anyone knows of a "slick" (or comparatively easy) way to remove 100s of dust or damaged emultion spots from 35 mm Kodachrome slide scans.  Actually they are not strictly scans but rather I'm working with RAW files produced by re-photographing the original slide with a slide copy attachment on my Nikon.  The slides were cleaned with a soft brush before being re-photographed, so the spots are really in the emulsion layers and not on the surface.  I can do the slides that aren't too badly degrades with the Spot Healing Brush tool.  Ones where there are litterally 100s if not a thousands spots take way too long to do with this tool.  Using the Dust & Scratches filter is a possible option but I find that most of the time getting rid of the dark spots causes a lot of collateral damage to the image.  

What I'd like to find is a way to isolate the dark spots maybe as a separate layer and then use them in some way to tell Photoshop to replace the dark spots with the surrounding color.  Any ideas? Is it even possible?  I can think of a relative straightforward way to design a filter algorithm to do this, but unfortunately Adobe has not done it (as far as I know).

[Myra Ferguson]

You might try using the frequency separation technique on them. It's a technique that's usually reserved for retouching skin, but it sounds like it might work here, too. Instead of removing blemishes, you'd be removing the dark spots. Here's a tutorial from Colin Smith on Photoshop Cafe showing how it works: https://www.youtube.com/watch?v=7XfoEHa_VjE

[Bill Junk]

This was an interesting and well done YouTube video, but a bit beyond my level of understand.  So I haven't ventured in this direction to see if there's potential.  Thank you for making the suggestion.

[r-bin]

To remove only dark dots, make a copy of the layer in Lighten mode, apply Dust & Scratches to it (select the desired radius and maximum allowable Threshold when all the dark dots disappear), hide the layer with a black mask and paint (show) in mask with a white brush those places where there are dark dots.

[Bill Junk · Accepted solution]

Thank you for your suggestion.  I did try a variation of this that produced better results than simply using the Dust & Scratches filter on the entire image of the Background layer.  I'm not very experienced with blend modes and often find them a bit mysterious.  What I did do was make a copy of the background layer, then used the Dust & Scratches filter on it to remove the majority of the smaller dark spots.  After that I used the Spot Healing Brush Tool on the duplicated layer to remove larger defects.  When the duplicated layer was cleaned to my satisfaction I then set the blend mode to Lighten which brought back some of the finer details that were "fuzzed out" by the Dust & Scratches tool.  The results were substantially better than what I had previously done with the Spot Healing Brush Tool because more of the small inperfections were removed while still keeping most of the detail.  I'm not exactly sure why or how it worked but if I proceed with this method on other seriously degrades images it will save me a lot of time.  As far as adding a layer mask goes, there are so many black spots randomly distributed, fairly densely, over the entire image that painting on the mask would seem to be just as much work as using the Spot Healing Brush (unless I don't fully understand your idea).

[Chuck Uebele · Accepted solution]

I would also suggest that you make a separate layer for the dust and scratches, then add a layer mask and paint out the areas there the dust and scratches cause issues with normal detail. 

[Bill Junk]

My reply to the message that preceeded yours basically applies here too.  Thank you for taking the time to give me an idea.

[Stephen Marsh]

I always had more success using the D&S filter using an irregular feathered selection around areas with dust. Perhaps fading to lighten or darken blend mode if it helped and then manually spotting as required. Of course working on a dupe of the background layer and masking as required. Sometimes one can sacrifice the majority of a picture that is not super critical in order to spend more time and care on the "hero".

Also consider final reproduction and image size, as one may not even see all this detail on the final output. 

[Norman Sanders]

I know I am a little late to the party but I am adding it in the event you find this technique useful.

1. Open the file
2. Cmd+J to create a duplicate layer
3. Filter > Blur > Gaussian Blur. Blur until the specks disappear
4. History Panel. Move the History Brush symbol down to Gaussian Blur step
5. History Panel. Choose the layer above the Gaussian Blur step. The specked version will reappear.
6. Choose the History Brush Tool (soft edged) and in its Options bar change the Mode to Darken
7. Paint the dust specks. You don’t need tiny brush and you may find, depending upon the subject, you can drag the brush