Purple marks on old slides

[shedder]

I've just joined this forum. Over the past year or so I've been digitizing my old negatives and slides, using A Nikon Coolscan V scanner, scanning to DNG format using Vuescan, and then editing using Photoshop CS3, finally saving as jpegs.

Recently I've started scanning some of my old slides (20-30 years old), and a significant number have blue/purple marks (mould?) on them, particularly in the darker areas of the slide. I've attached an example.

Can anyone suggest what I can do about this, either by way of treating/cleaning the slide, or some techniques I could use in photoshop?

[mistermonday]

That doesn't look like mold but then again I have never seen the likes of it on the thousands of slides that I have scanned. There are many of them so to minimize the effort, I would try the following:
Duplicate the background layer. Then Image>Apply Image and select either layer as the source, select the Red channel, blend mode normal, opacity 100%, OK. Change the blend mode of the layer (now grayscale) from normal to Luminosity. Add a blank layer on top with the blend mode set to Color. Choose a soft brush. Alt Click near a purple stain to sample the "good" color and now paint over all the purple dots. When you get to a different area like the red vest, take another color sample. You should be able to cover the image very quickly.
Depending on your image, sometimes the Green channel will be more even and show less of the purple spots so use it.
This scan is pretty small, noisy, and over pixelated, so I just shifted the level in the Blue channel.
Regards Murray

[Dave.Cox]

I have seen something similar to this, but usually in the red channel and not the blue channel. It looks to me like some uneven fading of the pigments in the slide. Most of the damage seems to be in the blue channel. I did most of the repair by healing in the blue channel. I then added a levels adjustment layer to get rid of the blue cast.

[chillin]

I used HSL + curves to get rid of the purple cast.
Healing brush took care of the bluish spots.
The difficult part was to clear the noise. I had to add noise couple of times with a darken & lighten blending, after that I've applied just a bit of noise ware.

[Graphics23]

I corrected this with three channel blends;

Green into Blue, Darken mode, 100%. Fixed spots and blue cast.
Red into Red, Linear Burn mode, 15%. Toned down clipped reds.
Green into Red, Darker Color mode, 30%. Improved detail in Red channel.

Then ran Reduce Noise filter. Very moderate settings.

Finished with an Exposure Adjustment layer set to lighten. Revealed just a little more detail in the shadows.

Regards,

Michael