Discoloration on slides

luizinho45 said:

I have tried the technique but I get either blotches of color or the stains change color but are still there.

I see on the video when he's painting, the stains completely vanish. I can't get that affect.

You need to make sure that the color you are picking to paint over the stains matches the color of the material underneath.  You may also have to play around with the layer blending mode depending on the color of the original photo versus the stain.

You're welcome.  Let us know how you get on and feel free to ask any further questions.  There are many different techniques that can be used to restore damaged photos.

I don't claim to be an expert on retouching photos, but since nobody else has stepped in here, I'll give you some options.  I do claim to be bilingual in English and American, so I will also try to tranlate the video that you linked which, I agree, is difficult to follow.  😀

So, the main technique in the video to remove the color spots is to paint over the spots with the colors of the neighboring pixels and to use a Color blend mode to make them disappear.  For your photo, here are the basic steps to take:

1. First duplicate the original image onto a new layer by opening the image in the Editor and pressing Ctrl+J.  I always take this step when editing an image so you can always go back to the original layer if you make a mistake.
2. Create a new empty layer.  (Shift+Ctrl+N).
3. Select the layer blend mode to Darker Color from the dropdown menu.  Depending on whether the color is darker or lighter than the spots, you can try other blend modes such as Color or Lighter Color.
4. Select the Brush tool.  (B)
5. Hold down the Alt key.  This will change the cursor to an eye-dropper color picker.  For the man's suit in the foreground, click on a dark area near the damage spots and release the Alt key.
6. Make sure that the empty layer is selected and start painting over the spots in the image.
7. Keep using the Alt key to change the color of the paint.  For example, on the sleeve in the foreground, the suit is slightly lighter.  So choose a color area near each spot before painting over the spot.

There is a lot of texture on the purple priest's robe on the right hand side, so simply using the Color Blend modes doesn't work so well.  Here, you should probably use the Clone tool to replace the spots with nearby portions of the robe.  First of all, create a new blank layer, make sure it is selected, and then start cloning.  You can do the same with the pink dress.

For some of the more defined spots, you can also use the Spot Healing tool.  For example, with the blue dress on the left of the photo.  Again, create a new empty layer and select it to make the changes with this tool.  And make sure the Sample All Layers box is checked.

Here is a before and after of some of the changes I was able to achieve using these techniques.  Since I am not sure of your experience level, I have probably left out a lot of details.  If you need more assistance, let us know. 

In case you don't know what I'm talking about with layer Blend Modes, here is where to look: